This C++-ifies iterate_over_threads, changing it to accept a
gdb::function_view and to return bool.
Approved-By: Simon Marchi <simon.marchi@efficios.com>
For background reading, please see the previous patch, and the patch
before that!
After the last two patches, internal breakpoints can now be marked as
shlib_disabled if the library in which they are placed is unloaded.
The patch before last discusses a situation related to the
gdb.base/nostdlib.exp test, when run on a GNU/Linux glibc based system
where executables are compiled as PIE by default.
In this case it is observed that the dynamic linker will actually
report itself as unloaded (i.e. remove itself from the list of
currently loaded shared libraries). This behaviour is likely a bug in
the dynamic linker, but this behaviour exists in released versions of
the dynamic linker, so GDB should (if the cost is not too great) be
changed to handle this situation.
This commit handles a problem with the 'maint info breakpoints'
command.
When the dynamic linker is unloaded the 'shlib event' breakpoint is
marked as shlib_disabled (i.e. placed into the pending state). When
displaying the breakpoint in the 'maint info breakpoints' output, GDB
will try to print the locspec (location_spec *) as a string
Unfortunately, the locspec will be nullptr as the internal breakpoints
are not created via a location_spec, this means that GDB ends up
trying to call location_sepc::to_string() on a nullptr, resulting in
undefined behaviour (and a crash).
For most internal breakpoint types this is not a problem. If we
consider bp_longjmp_master for example, if the shared library
containing a breakpoint of this type is unloaded then first GDB marks
the breakpoint as shlib_disabled, then after unloading the shared
library breakpoint_re_set is called, which will delete the internal
breakpoint, and then try to re-create it (if needed). As a result,
the user never gets a change to run 'maint info breakpoints' on a
bp_longjmp_master breakpoint in the shlib_disabled state.
But bp_shlib_event and bp_thread_event breakpoints are not deleted and
recreated like this (see internal_breakpoint::re_set), so it is
possible, in rare cases, that we could end up trying to view one of
these breakpoint in a shlib_disabled state, and it would be nice if
GDB didn't crash as a result.
I've updated the printing code to check for and handle this case, and
I've updated the docs to mention this (rare) case.
For testing, I've extended gdb.base/nostdlib.exp to compile as
pie and nopie, and then run 'maint info breakpoints'. If we're
running on a buggy glibc then this will trigger the crash. I don't
know how I can trigger this problem without a buggy glibc as this
would require forcing the dynamic linker to be unloaded.
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Tom Tromey <tom@tromey.com>
Bug PR gdb/32079 highlights an issue where GDB will try to remove a
breakpoint for a shared library that has been unloaded. This will
trigger an error from GDB like:
(gdb) next
61 dlclose (handle[dl]);
(gdb) next
warning: error removing breakpoint 0 at 0x7ffff78169b9
warning: error removing breakpoint 0 at 0x7ffff7730b57
warning: error removing breakpoint 0 at 0x7ffff7730ad3
54 for (dl = 0; dl < 4; ++dl)
(gdb)
What happens is that as the inferior steps over the dlclose() call,
GDB notices that the library has been unloaded and calls
disable_breakpoints_in_unloaded_shlib. However, this function only
operates on user breakpoints and tracepoints.
In the example above what is happening is that the test loads multiple
copies of libc into different linker namespsaces. When we 'next' over
the dlclose call one of the copies of libc is unloaded. As GDB placed
longjmp master breakpoints within the copy of libc that was just
unloaded, the warnings we see are GDB trying (and failing) to remove
these breakpoints.
I think the solution is for disable_breakpoints_in_unloaded_shlib to
handle all breakpoints, even internal ones like the longjmp master
breakpoints.
If we do this then the breakpoint will be marked as shlib_disabled and
also will be marked as not inserted. Later when we call
breakpoint_re_set() and the longjmp breakpoints are deleted we will no
longer try to remove them.
This solution is inspired by a patch suggested in the bug report:
https://sourceware.org/bugzilla/show_bug.cgi?id=32079#c3
There are some differences with my approach compared to the patch
suggested in the bug. First I have no need to delete the breakpoint
inside disable_breakpoints_in_unloaded_shlib as an earlier patch in
this series arranged for breakpoint_re_set to be called when shared
libraries are removed. Calling breakpoint_re_set will take care of
deleting the breakpoint for us. For details see the earlier commit
titled:
gdb: fixes for code_breakpoint::disabled_by_cond logic
Next, rather than only handling bp_longjmp and bp_longjmp_master, I
allow all breakpoints to be handled. I also only give the warning
about disabling breakpoints for user breakpoints, I don't see the
point of warning the user about internal b/p changes.
With this done the issues in PR gdb/32079 are resolved.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32079
Tested-By: Hannes Domani <ssbssa@yahoo.de>
Approved-By: Tom Tromey <tom@tromey.com>
This commit removes the clearing of bp_location::inserted from
disable_breakpoints_in_unloaded_shlib, my claim is that this call is
not needed (any more), and with the next commit, this line actually
causes some problems.
The disable_breakpoints_in_unloaded_shlib function was added back in
2004 with commit 84acb35a5a, and from this first version the
function cleared the bp_location::inserted flag. The motivation for
this is that the shared library might have already been unmapped, in
which case, a later attempt to remove the location could fail.
In 2013 a similar function disable_breakpoints_in_freed_objfile was
added. This function also cleared bp_location::inserted for similar
reasons. This code was added in commit:
commit 63644780ba
Date: Tue Mar 12 11:10:18 2013 +0100
New remove-symbol-file command.
Then in 2014 the clearing of bp_location::inserted was removed from
disable_breakpoints_in_freed_objfile in the commit:
commit 08351840ea
Date: Tue Apr 22 23:19:19 2014 +0100
Stale breakpoint instructions, spurious SIGTRAPS.
The reason that clearing the ::inserted flag was removed in this
commit is that if the disable_breakpoints_in_freed_objfile function
was called when the b/p were actually inserted, and the memory for the
associated objfile wasn't actually unmapped, then we could end up
leaving breakpoints inserted into the inferior, which leads to
spurious SIGTRAPs.
In the next commit I'll change disable_breakpoints_in_unloaded_shlib
so that all breakpoints, not just user breakpoints, will be
disabled (via shlib_disabled) when a shared library is unloaded. This
addresses PR gdb/32079, see the next commit for a fuller justification
for this change.
The problem is that when I tested the next commit I ran into some
regressions from the gdb.base/nostdlib.exp test when run on an AArch64
GNU/Linux system where executables are compiled as PIE by default.
This test compiles a simple binary with the -nostdlib flag.
What happens is this:
- The executable is compiled as PIE, this means that we get a
dynamically linked executable, the dynamic linker is used to
perform the PIE relocation, but the executable uses no other
shared libraries.
- When GDB starts the inferior, initially the dynamic linker is
discovered as a shared library being used by the application, GDB
loads in the library and its debug symbols, placing the internal
"shlib event" breakpoints so that future shared library events can
be tracked.
- For the target I tested on systemtap probes were not used, instead
GDB fell back to the old style even breakpoint.
- As the inferior progresses, after the PIE relocation has been
performed, the dynamic linker performs some house keeping on the
list of shared libraries being used by the application. During
this process the dynamic linker is removed from the list of shared
libraries being used by the inferior, this causes GDB see a shared
library event, which GDB understands to mean that it should unload
the dynamic linker from the inferior.
I spoke with the glibc engineers at RH, and the feeling is that
this is likely a bug (it's still being investigated). But I don't
think it really matters if this is a bug or not. There are
versions of glibc in the wild that have this behaviour, so GDB
should (if the cost is not too great) be updated to handle this.
Obviously after removing the dynamic linker from the list of
shared libraries, the dynamic linker is not actually unmapped,
that would not be possible, it's the dynamic linker that does the
unmapping, so the dynamic linker is left mapped into the
inferior's address space.
- With the next patch in place all breakpoints (user and internal)
within the dynamic linker are disabled (shlib_disabled) and
currently marked as not inserted (bp_location::inserted flag is
cleared).
- Having processed the shared library event GDB then resumes the
inferior. As the shared library event is not a full stop of the
inferior (i.e. we don't remove all breakpoints before handling the
event), all of the breakpoints in the dynamic linker are still
inserted, but are now marked as not-inserted.
- GDB then resumes the inferior and immediately hits the breakpoint
that is still inserted. As GDB thinks this breakpoint is not
inserted, this is reported to the user as a SIGTRAP.
The fix I think is just to not clear the bp_location::inserted flag in
disable_breakpoints_in_unloaded_shlib. This will leave the breakpoint
as inserted in the case above. GDB will now be able to successfully
resume the inferior after the shared library event (knowing there is a
breakpoint inserted GDB will step over it and continue as expected).
The next time the inferior performs a full stop the now shlib_disabled
breakpoint will be removed from the inferior we would want.
For the usual case, where a shared library is being unloaded due to
say a dlclose, the breakpoints in the library will be marked as
disabled, but will be left inserted. The next time remove_breakpoints
is called GDB will try to remove those breakpoint locations. If the
removal fails, as the breakpoint is marked shlib_disabled, GDB will
hide the error message from the user and just assume that the shared
library has been unmapped. This functionality was first added in 2008
in commit 879d1e6b46.
There are two aspects to testing this change. First whether no
clearing the ::inserted flag causes general problems. That is tested
by running the full testsuite (I see no regressions).
Then there is the specific problem that caused me to make this
change. That issue only occurs on AArch64, with GNU/Linux using
glibc, when the executable is compiled as PIE, and doesn't use any
shared libraries other than the dynamic linker (which can be the
gdb.base/nostdlib.exp test if run on the right system). What I don't
know is how to recreate this setup in a more general form.
We can't use add-symbol-file/remove-symbol-file as that passes through
disable_breakpoints_in_freed_objfile instead, which the ::installed
flag is already not adjusted.
Also the bug doesn't trigger on x86 targets due to code in
handle_signal_stop which sees the inserted breakpoint, and decides
this must be a breakpoint that actually exists in the program, and
then because gdbarch_decr_pc_after_break returns non-zero for x86, GDB
steps the inferior past the breakpoint. This is the big difference
from AArch64 where gdbarch_decr_pc_after_break returns zero, and so
the inferior gets stuck hitting the unexpectedly inserted breakpoint.
Approved-By: Tom Tromey <tom@tromey.com>
While working on the previous commit I realised that GDB would not
handle dprintf breakpoints correctly when a shared library was
unloaded.
Consider this example using the test binary from shlib-unload.exp. In
the function 'foo' we create a dprintf is in a shared library:
(gdb) b 59
Breakpoint 1 at 0x401215: file /tmp/projects/binutils-gdb/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/shlib-unload.c, line 59.
(gdb) r
Starting program: /tmp/projects/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/shlib-unload/shlib-unload
Breakpoint 1, main () at /tmp/projects/binutils-gdb/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/shlib-unload.c:59
59 res = dlclose (handle); /* Break here. */
(gdb) dprintf foo,"In foo"
Dprintf 2 at 0x7ffff7fc50fd: file /tmp/projects/binutils-gdb/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/shlib-unload-lib.c, line 23.
(gdb) n
Error in re-setting breakpoint 2: Function "foo" not defined.
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
warning: error removing breakpoint 2 at 0x7ffff7fc50fd
Cannot remove breakpoints because program is no longer writable.
Further execution is probably impossible.
60 assert (res == 0);
(gdb)
What happens here is that as the inferior steps over the dlclose call
the shared library containing 'foo' is unloaded and
disable_breakpoints_in_unloaded_shlib is called. However in
disable_breakpoints_in_unloaded_shlib we have this check:
if (b.type != bp_breakpoint
&& b.type != bp_jit_event
&& b.type != bp_hardware_breakpoint
&& !is_tracepoint (&b))
continue;
As the dprintf has type bp_dprintf then this check triggers and we
ignore the dprintf, meaning the dprintf is not disabled. When the
inferior stops after the 'next' GDB tries to remove all breakpoints
but the dprintf can no longer be removed, the memory in which it was
placed has been unmapped from the inferior.
The fix is to start using is_breakpoint() in
disable_breakpoints_in_unloaded_shlib instead of the bp_breakpoint and
bp_hardware_breakpoint checks. The is_breakpoint() function also
checks for bp_dprintf.
With this fix in place GDB now correctly disables the breakpoint and
we no longer see the warning about removing the breakpoint.
During review it was pointed out that PR gdb/23149 and PR gdb/20208
both describe something similar, though for these bugs, the inferior
is restarted (which unloads all currently loaded shlib) rather than
passing over the dlclose. But the consequences are pretty similar.
I've included a test which covers this case.
One additional thing that these two bugs did show though is that
disable_breakpoints_in_shlibs also needs to start using is_breakpoint
for the same reason. Without this change, when an inferior is
restarted we get a warning like this for dprintf breakpoints:
warning: Temporarily disabling breakpoints for unloaded shared library "..."
but we don't get a similar warning for "normal" breakpoints. This is
because disable_breakpoints_in_shlibs is called from clear_solib,
which is called when an inferior is restarted.
It is best not to think too hard about disable_breakpoints_in_shlibs,
as this function is pretty broken, e.g. it doesn't call
notify_breakpoint_modified, despite modifying the breakpoints. But
for now I'm ignoring that, but fixing this is definitely on my list
for my next set of breakpoint related fixes, it's just that a lot of
these breakpoint fixes end up being depending on one another, but I
want to avoid making this series too long. So for now, I'm ignoring
the existing bug (missing breakpoint modified events), and fixing
disable_breakpoints_in_shlibs to cover dprintf.
With these fixes in place, the two bugs mentioned above should be
fixed.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=23149
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=20208
Tested-By: Hannes Domani <ssbssa@yahoo.de>
Approved-By: Tom Tromey <tom@tromey.com>
This commit rewrites disable_breakpoints_in_unloaded_shlib to be more
like disable_breakpoints_in_freed_objfile. Instead of looping over
all b/p locations, we instead loop over all b/p and then over all
locations for each b/p.
The advantage of doing this is that we can fix the small bug that was
documented in a comment in the code:
/* This may cause duplicate notifications for the same breakpoint. */
notify_breakpoint_modified (b);
By calling notify_breakpoint_modified() as we modify each location we
can potentially send multiple notifications for a single b/p.
Is this a bug? Maybe not. After all, at each notification one of the
locations will have changed, so its probably fine. But it's not
ideal, and we can easily do better, so lets do that.
There's a new test which checks that we only get a single notification
when the shared library is unloaded. Note that the test is written as
if there are multiple related but different tests within the same test
file ... but there aren't currently! The next commit will add another
test proc to this test script at which point the comments will make
sense. I've done this to avoid unnecessary churn in the next commit.
Tested-By: Hannes Domani <ssbssa@yahoo.de>
Approved-By: Tom Tromey <tom@tromey.com>
I spotted that the code_breakpoint::disabled_by_cond flag doesn't work
how I'd expect it too. The flag appears to be "sticky" in some
situations; once a code_breakpoint::disabled_by_cond flag is marked
true, then, in some cases the flag wont automatically become false
again, even when you'd think it should.
The problem is in update_breakpoint_locations. In this function,
which is called as a worker of code_breakpoint::re_set, GDB computes a
new set of locations for a breakpoint, the new locations are then
installed into the breakpoint.
However, before installing the new locations GDB attempts to copy the
bp_location::enabled and bp_location::disabled_by_cond flag from the
old locations into the new locations.
The reason for copying the ::enabled flag makes sense. This flag is
controlled by the user. When we create the new locations if GDB can
see that a new location is equivalent to one of the old locations, and
if the old location was disabled by the user, then the new location
should also be disabled.
However, I think the logic behind copying the ::disabled_by_cond flag
is wrong. The disabled_by_cond flag is controlled by GDB and should
toggle automatically. If the condition string can be parsed then the
flag should be false (b/p enabled), if the condition string can't be
parsed then the flag should be true (b/p disabled).
As we always parse the condition string in update_breakpoint_locations
before we try to copy the ::enabled flag value then the
::disabled_by_cond flag should already be correct, there's no need to
copy over the ::disabled_by_cond value from the old location.
As a concrete example, consider a b/p placed within the main
executable, but with a condition that depends on a variable within a
shared library.
When the b/p is initially created the b/p will be disabled as the
condition string will be invalid (the shared library variable isn't
available yet).
When the inferior starts the shared library is loaded and the
condition variable becomes available to GDB. When the shared library
is loaded breakpoint_re_set is called which (eventually) calls
update_breakpoint_locations.
A new location is computed for the breakpoint and the condition string
is parsed. As the shared library variable is now know the expression
parses correctly and ::disabled_by_cond is left false for the new
location.
But currently GDB spots that the new location is at the same address
as the old location and copies disabled_by_cond over from the old
location, which marks the b/p location as disabled. This is not what
I would expect.
The solution is simple, don't copy over disabled_by_cond.
While writing a test I found another problem though. The
disabled_by_cond flag doesn't get set true when it should! This is
the exact opposite of the above.
The problem here is in solib_add which is (despite the name) called
whenever the shared library set changes, including when a shared
library is unloaded.
Imagine an executable that uses dlopen/dlclose to load a shared
library. Given an example of a b/p in the main executable that has a
condition that uses a variable from our shared library, a library
which might be unloaded with dlclose.
My expectation is that, when the library is unloaded, GDB will
automatically mark the breakpoint as disabled_by_cond, however, this
was not happening.
The problem is that in solib_add we only call breakpoint_re_set when
shared libraries are added, not when shared libraries are removed.
The solution I think is to just call breakpoint_re_set in both cases,
now the disabled_by_cond flag is updated as I'd expect.
Unfortunately, making this change causes a regression when running:
make check-gdb \
TESTS="gdb.trace/change-loc.exp" \
RUNTESTFLAGS="--target_board=native-gdbserver"
This test unloads a shared library and expects breakpoints within the
shared library to enter the PENDING state (because the bp_location's
shlib_disabled flag will be set). However, the new call to
breakpoint_re_set means that this is no longer the case.
The breakpoint_re_set call means that update_breakpoint_locations is
called, which then checks if all locations for a breakpoint are
pending or not. In this test not all locations are pending, and so
GDB recalculates the locations of each breakpoint, this means that
pending locations are discarded.
There is a but report PR gdb/32404 which mentions the problems with
shlib_disabled pending breakpoints, and how they are prone to being
randomly deleted if the user can cause GDB to trigger a call to
breakpoint_re_set. This patch just adds another call to
breakpoint_re_set, which triggers this bug in this one test case.
For now I have marked this test as KFAIL. I do plan to try and
address the pending (shlib_disabled) breakpoint problem in the future,
but I'm not sure when that will be right now.
There are, of course, tests to cover all these cases.
During review I was pointed at bug PR gdb/32079 as something that this
commit might fix, or help in fixing.
And this commit is part of the fix for that bug, but is not the
complete solution. However, the remaining parts of the fix for that
bug are not really related to the content of this commit.
The problem in PR gdb/32079 is that the inferior maps multiple copies
of libc in different linker namespaces using dlmopen (actually libc is
loaded as a consequence of loading some other library into a different
namespace, but that's just a detail). The user then uses a 'next'
command to move the inferior forward.
GDB sets up internal breakpoints on the longjmp symbols, of which
there are multiple copies (there is a copy in every loaded libc).
However, the 'next' command is, in the problem case, stepping over a
dlclose call which unloads one of the loaded libc libraries.
In current HEAD GDB in solib_add we fail to call breakpoint_re_set()
when the library is unloaded; breakpoint_re_set() would delete and
then recreate the longjmp breakpoints. As breakpoint_re_set() is not
called GDB thinks that the the longjmp breakpoint in the now unloaded
libc still exists, and is still inserted.
When the inferior stops after the 'next' GDB tries to delete and
remove the longjmp breakpoint which fails as the libc in which the
breakpoint was inserted is no longer mapped in.
When the user tries to 'next' again GDB tries to re-insert the still
existing longjmp breakpoint which again fails as the memory in which
the b/p should be inserted is no longer part of the inferior memory
space.
This commit helps a little. Now when the libc library is unmapped GDB
does call breakpoint_re_set(). This deletes the longjmp breakpoints
including the one in the unmapped library, then, when we try to
recreate the longjmp breakpoints (at the end of breakpoint_re_set) we
don't create a b/p in the now unmapped copy of libc.
However GDB does still think that the deleted breakpoint is inserted.
The breakpoint location remains in GDB's data structures until the
next time the inferior stops, at which point GDB tries to remove the
breakpoint .... and fails.
However, as the b/p is now deleted, when the user tries to 'next' GDB
no longer tries to re-insert the b/p, and so one of the problems
reported in PR gdb/32079 is resolved.
I'll fix the remaining issues from PR gdb/32079 in a later commit in
this series.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32079
Tested-By: Hannes Domani <ssbssa@yahoo.de>
Approved-By: Tom Tromey <tom@tromey.com>
Consider the gdb.base/dlmopen.exp test case. The executable in this
test uses dlmopen to load libraries into multiple linker namespaces.
When a library is loaded into a separate namespace, its dependencies
are also loaded into that namespace.
This means that an inferior can have multiple copies of some
libraries, including the dynamic linker, loaded at once.
However, glibc optimises at least the dynamic linker case. Though the
library appears to be mapped multiple times (it is in the inferior's
solib list multiple times), there is really only one copy mapped into
the inferior's address space. Here is the 'info sharedlibrary' output
on an x86-64/Linux machine once all the libraries are loaded:
(gdb) info sharedlibrary
From To Syms Read Shared Object Library
0x00007ffff7fca000 0x00007ffff7ff03f5 Yes /lib64/ld-linux-x86-64.so.2
0x00007ffff7eda3d0 0x00007ffff7f4e898 Yes /lib64/libm.so.6
0x00007ffff7d0e800 0x00007ffff7e6dccd Yes /lib64/libc.so.6
0x00007ffff7fbd040 0x00007ffff7fbd116 Yes /tmp/build/gdb/testsuite/outputs/gdb.base/dlmopen/dlmopen-lib.1.so
0x00007ffff7fb8040 0x00007ffff7fb80f9 Yes /tmp/build/gdb/testsuite/outputs/gdb.base/dlmopen/dlmopen-lib-dep.so
0x00007ffff7bfe3d0 0x00007ffff7c72898 Yes /lib64/libm.so.6
0x00007ffff7a32800 0x00007ffff7b91ccd Yes /lib64/libc.so.6
0x00007ffff7fca000 0x00007ffff7ff03f5 Yes /lib64/ld-linux-x86-64.so.2
0x00007ffff7fb3040 0x00007ffff7fb3116 Yes /tmp/build/gdb/testsuite/outputs/gdb.base/dlmopen/dlmopen-lib.1.so
0x00007ffff7fae040 0x00007ffff7fae0f9 Yes /tmp/build/gdb/testsuite/outputs/gdb.base/dlmopen/dlmopen-lib-dep.so
0x00007ffff7ce1040 0x00007ffff7ce1116 Yes /tmp/build/gdb/testsuite/outputs/gdb.base/dlmopen/dlmopen-lib.1.so
0x00007ffff7cdc040 0x00007ffff7cdc0f9 Yes /tmp/build/gdb/testsuite/outputs/gdb.base/dlmopen/dlmopen-lib-dep.so
0x00007ffff79253d0 0x00007ffff7999898 Yes /lib64/libm.so.6
0x00007ffff7759800 0x00007ffff78b8ccd Yes /lib64/libc.so.6
0x00007ffff7fca000 0x00007ffff7ff03f5 Yes /lib64/ld-linux-x86-64.so.2
0x00007ffff7cd7040 0x00007ffff7cd7116 Yes /tmp/build/gdb/testsuite/outputs/gdb.base/dlmopen/dlmopen-lib.2.so
Notice that every copy of /lib64/ld-linux-x86-64.so.2 is mapped at the
same address.
As the inferior closes the libraries that it loaded, the various
copies of the dynamic linker will also be unloaded.
Currently, when this happens GDB calls notify_solib_unloaded, which
triggers the gdb::observers::solib_unloaded observer. This observer
will call disable_breakpoints_in_unloaded_shlib (in breakpoint.c),
which disables any breakpoints in the unloaded solib.
The problem with this, is that, when the dynamic linker (or any solib)
is only really mapped once as is the case here, we only want to
disable breakpoints in the library when the last instance of the
library is unloaded.
The first idea that comes to mind is that GDB should not emit the
solib_unloaded notification if a shared library is still in use,
however, this could break MI consumers.
Currently, every time a copy of ld-linux-x86-64.so.2 is unloaded,
GDB's MI interpreter will emit a =library-unloaded event. An MI
consumer might use this to update the library list that it displays to
the user, and fewer notify_solib_unloaded calls will mean fewer MI
events, which will mean the MI consumer's library list could get out
of sync with GDB.
Instead I propose that we extend GDB's solib_unloaded event to add a
new flag. The new flag indicates if the library mapping is still in
use within the inferior. Now the MI will continue to emit the
expected =library-unloaded events, but
disable_breakpoints_in_unloaded_shlib can check the new flag, when it
is true (indicating that the library is still mapped into the
inferior), no breakpoints should be disabled.
The other user of the solib_unloaded observer, in bsd-uthread.c,
should, I think, do nothing if the mapping is still in use. This
observer is also disabling breakpoints when a library is unloaded.
Most of the changes in this commit relate to passing the new flag
around for the event. The interesting changes are mostly in solib.c,
where the flag value is determined, and in breakpoint.c and
bsd-uthread.c, where the flag value is read.
There's a new MI test, the source of which is mostly copied from the
gdb.base/dlmopen.exp test. This new test is checking we see all the
expected =library-unloaded events.
'rbreak' searches symbols and then sets a number of breakpoints. If
setting one of the breakpoints fails, then 'rbreak' will terminate
before examining the remaining symbols.
However, it seems to me that it is better for 'rbreak' to keep going
in this situation. That is what this patch implements.
This problem can be seen by writing an Ada program that uses "pragma
import" to reference a symbol that does not have debug info. In this
case, the program will link but setting a breakpoint on the imported
name will not work.
I don't think it's possible to write a reliable test for this, as it
depends on the order in which symtabs are examined.
New in v2: rbreak now shows how many breakpoints it made and also how
many errors it encountered.
Regression tested on x86-64 Fedora 40.
Approved-By: Andrew Burgess <aburgess@redhat.com>
This adds a new "command" style that is used when styling the name of
a gdb command.
Note that not every instance of a command name that is output by gdb
is changed here. There is currently no way to style error() strings,
and there is no way to mark up command help strings.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31747
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Reviewed-By: Keith Seitz <keiths@redhat.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>
Make the 'struct breakpoint *' argument 'const' in user_breakpoint_p
and pending_breakpoint_p. And make the 'struct bp_location *'
argument 'const' in bl_address_is_meaningful.
There should be no user visible changes after this commit.
This converts breakpoint.c to use the new hash table.
Change-Id: I6d997a6242969586a7f8f9eb22cc8dd8d3ac97ff
Co-Authored-By: Tom Tromey <tom@tromey.com>
Approved-By: Tom Tromey <tom@tromey.com>
The breakpoint_free_objfile function is called from the objfile
destructor, and has the job of removing references to the soon to be
deleted objfile from all breakpoint locations.
The current implementation of breakpoint_free_objfile seems to miss
lots of possible objfile references within bp_location. Currently we
only check if bp_location::symtab is associated with the objfile in
question, but there's bp_location::section and bp_location::probe,
both of which might reference the soon to be deleted objfile.
Additionally bp_location::symbol and bp_location::msymbol if set will
surely be related to the objfile and should also be cleaned up.
I'm not aware that this causes any problems, but it doesn't seem like
a good idea to retain pointers to deleted state, so I propose that we
improve breakpoint_free_objfile to set these pointers back to nullptr.
In the future I plan to investigate the possibility of merging the
functionality of breakpoint_free_objfile into
disable_breakpoints_in_freed_objfile which is called via the
gdb::observers::free_objfile event. However, I already have a patch series
in progress which touches this area of GDB, and I'd like to avoid
conflicting with that earlier series:
https://inbox.sourceware.org/gdb-patches/cover.1724948606.git.aburgess@redhat.com
Once this patch, and that earlier series have landed then I'll see if
I can merge breakpoint_free_objfile, but I don't think that this needs
to block this patch.
There should be no user visible changes after this commit.
In update_breakpoint_locations there's a scope block which I don't
think adds any value. There is one local defined within the scope,
the local is currently an 'int' but should be a 'bool', either way
there's no destructor being triggered when we exit the scope.
This commit changes the local to a 'bool', removes the unnecessary
scope, and re-indents the code.
Within the (now removed) scope was a `for' loop. Inside the loop I
have converted this:
for (....)
{
if (CONDITION)
{
/* Body */
}
}
to this:
for (....)
{
if (!CONDITION)
continue;
/* Body */
}
which means that the body doesn't need to be indented as much, making
things easier to read.
There should be no functional change after this commit.
Reviewed-By: Klaus Gerlicher <klaus.gerlicher@intel.com>
The gdbarch function gdbarch_remove_non_address_bits adjusts addresses to
enable debugging of programs with tagged pointers on Linux, for instance for
ARM's feature top byte ignore (TBI).
Once the function is implemented for an architecture, it adjusts addresses for
memory access, breakpoints and watchpoints.
Linear address masking (LAM) is Intel's (R) implementation of tagged
pointer support. It requires certain adaptions to GDB's tagged pointer
support due to the following:
- LAM supports address tagging for data accesses only. Thus, specifying
breakpoints on tagged addresses is not a valid use case.
- In contrast to the implementation for ARM's TBI, the Linux kernel supports
tagged pointers for memory access.
This patch makes GDB's tagged pointer support configurable such that it is
possible to enable the address adjustment for a specific feature only (e.g
memory access, breakpoints or watchpoints). This way, one can make sure
that addresses are only adjusted when necessary. In case of LAM, this
avoids unnecessary parsing of the /proc/<pid>/status file to get the
untag mask.
Reviewed-By: Felix Willgerodt <felix.willgerodt@intel.com>
(AArch64) Tested-By: Luis Machado <luis.machado@arm.com>
Approved-By: Luis Machado <luis.machado@arm.com>
I searched for spots using ".reset (new ...)" and replaced most of
these with std::make_unique. I think this is a bit cleaner and more
idiomatic.
Regression tested on x86-64 Fedora 40.
Reviewed-By: Klaus Gerlicher<klaus.gerlicher@intel.com>
On arm-linux, with test-case gdb.base/scope-hw-watch-disable.exp I run into:
...
(gdb) awatch a^M
Can't set read/access watchpoint when hardware watchpoints are disabled.^M
(gdb) PASS: $exp: unsuccessful attempt to create an access watchpoint
rwatch b^M
Can't set read/access watchpoint when hardware watchpoints are disabled.^M
(gdb) PASS: $exp: unsuccessful attempt to create a read watchpoint
continue^M
Continuing.^M
^M
Program received signal SIGSEGV, Segmentation fault.^M
0xf7ec82c8 in ?? () from /lib/arm-linux-gnueabihf/libc.so.6^M
(gdb) FAIL: $exp: continue until exit
...
Using "maint info break", we can see that the two failed attempts to set a
watchpoint each left behind a stale "watchpoint scope" breakpoint:
...
-5 watchpoint scope del y 0xf7ec569a inf 1
-5.1 y 0xf7ec569a inf 1
stop only in stack frame at 0xfffef4f8
-6 watchpoint scope del y 0xf7ec569a inf 1
-6.1 y 0xf7ec569a inf 1
stop only in stack frame at 0xfffef4f8
...
The SIGSEGV is a consequence of the stale "watchpoint scope" breakpoint: the
same happens if we:
- have can-use-hw-watchpoints == 1,
- set one of the watchpoints, and
- continue to exit.
The problem is missing symbol info on libc which is supposed to tell which
code is thumb. After doing "set arm fallback-mode thumb" the SIGSEGV
disappears.
Extend the test-case to check the "maint info break" command before and after
the two failed attempts, to make sure that we catch the stale
"watchpoint scope" breakpoints also on x86_64-linux.
Fix this in watch_command_1 by moving creation of the "watchpoint scope"
breakpoint after the call to update_watchpoint.
Tested on x86_64-linux.
PR breakpoints/31860
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31860
The commit:
commit 6cce025114
Date: Fri Mar 3 19:03:15 2023 +0000
gdb: only insert thread-specific breakpoints in the relevant inferior
added a couple of calls to breakpoint::clear_locations() inside
update_breakpoint_locations().
The intention of these calls was to avoid leaving redundant locations
around when a thread- or inferior-specific breakpoint was switched
from one thread or inferior to another.
Without the clear_locations() calls the tests gdb.multi/tids.exp and
gdb.multi/pending-bp.exp have some failures. A b/p is changed such
that the program space it is associated with changes. This triggers a
call to breakpoint_re_set_one() but the FILTER_PSPACE argument will be
the new program space. As a result GDB correctly calculates the new
locations and adds these to the breakpoint, but the old locations, in
the old program space, are incorrectly retained. The call to
clear_locations() solves this by deleting the old locations.
However, while working on another patch I realised that the approach
taken here is not correct. The FILTER_PSPACE argument passed to
breakpoint_re_set_one() and then on to update_breakpoint_locations()
might not be the program space to which the breakpoint is associated.
Consider this example:
(gdb) file /tmp/hello.x
Reading symbols from /tmp/hello.x...
(gdb) start
Temporary breakpoint 1 at 0x401198: file hello.c, line 18.
Starting program: /tmp/hello.x
Temporary breakpoint 1, main () at hello.c:18
18 printf ("Hello World\n");
(gdb) break main thread 1
Breakpoint 2 at 0x401198: file hello.c, line 18.
(gdb) info breakpoints
Num Type Disp Enb Address What
2 breakpoint keep y 0x0000000000401198 in main at hello.c:18
stop only in thread 1
(gdb) add-inferior -exec /tmp/hello.x
[New inferior 2]
Added inferior 2 on connection 1 (native)
Reading symbols from /tmp/hello.x...
(gdb) info breakpoints
Num Type Disp Enb Address What
2 breakpoint keep y <PENDING> main
stop only in thread 1.1
Notice that after creating the second inferior and loading a file the
thread-specific breakpoint was incorrectly made pending. Loading the
exec file in the second inferior triggered a call to
breakpoint_re_set() with the new, second, program space as the
current_program_space.
This program space ends up being passed to
update_breakpoint_locations().
In update_breakpoint_locations this condition is true:
if (all_locations_are_pending (b, filter_pspace) && sals.empty ())
and so we end up discarding all of the locations for this breakpoint,
making the breakpoint pending.
What we really want to do in update_breakpoint_locations() is, for
thread- or inferior- specific breakpoints, delete any locations which
are associated with a program space that this breakpoint is NOT
associated with.
But then I realised the answer was easier than that.
The ONLY time that a b/p can have locations associated with the
"wrong" program space like this is at the moment we change the thread
or inferior the b/p is associated with by calling
breakpoint_set_thread() or breakpoint_set_inferior().
And so, I think the correct solution is to hoist the call to
clear_locations() out of update_breakpoint_locations() and place a
call in each of the breakpoint_set_{thread,inferior} functions.
I've done this, and added a couple of new tests. All of which are
now passing.
Approved-By: Tom Tromey <tom@tromey.com>
This patch adds separate styling for line numbers. That is, whenever
gdb prints a source line number, it uses this style.
v2 includes a change to ensure that %ps works in query.
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Reviewed-by: Keith Seitz <keiths@redhat.com>
Spotted a comment in code_breakpoint::re_set_default that was added in
commit:
commit 6cce025114
Date: Fri Mar 3 19:03:15 2023 +0000
gdb: only insert thread-specific breakpoints in the relevant inferior
that was incorrect. The comment was not updated to take inferior
specific breakpoints into account.
This commit just updates the comment, there's no user visible changes
after this commit.
This commit updates GDB so that thread or inferior specific
breakpoints are only inserted into the program space in which the
specific thread or inferior is running.
In terms of implementation, getting this basically working is easy
enough, now that a breakpoint's thread or inferior field is setup
prior to GDB looking for locations, we can easily use this information
to find a suitable program_space and pass this to as a filter when
creating the sals.
Or we could if breakpoint_ops::create_sals_from_location_spec allowed
us to pass in a filter program_space.
So, this commit extends breakpoint_ops::create_sals_from_location_spec
to take a program_space argument, and uses this to filter the set of
returned sals. This accounts for about half the change in this patch.
The second set of changes starts from breakpoint_set_thread and
breakpoint_set_inferior, this is called when the thread or inferior
for a breakpoint changes, e.g. from the Python API.
Previously this call would never result in the locations of a
breakpoint changing, after all, locations were inserted in every
program space, and we just use the thread or inferior variable to
decide when we should stop. Now though, changing a breakpoint's
thread or inferior can mean we need to figure out a new set of
breakpoint locations.
To support this I've added a new breakpoint_re_set_one function, which
is like breakpoint_re_set, but takes a single breakpoint, and just
updates the locations for that one breakpoint. We only need to call
this function if the program_space in which a breakpoint's thread (or
inferior) is running actually changes. If the program_space does
change then we call the new breakpoint_re_set_one function passing in
the program_space which should be used to filter the new locations (or
nullptr to indicate we should set locations in all program spaces).
This filter program_space needs to propagate down to all the re_set
methods, this accounts for the remaining half of the changes in this
patch.
There were a couple of existing tests that created thread or inferior
specific breakpoints and then checked the 'info breakpoints' output,
these needed updating. These were:
gdb.mi/user-selected-context-sync.exp
gdb.multi/bp-thread-specific.exp
gdb.multi/multi-target-continue.exp
gdb.multi/multi-target-ping-pong-next.exp
gdb.multi/tids.exp
gdb.mi/new-ui-bp-deleted.exp
gdb.multi/inferior-specific-bp.exp
gdb.multi/pending-bp-del-inferior.exp
I've also added some additional tests to:
gdb.multi/pending-bp.exp
I've updated the documentation and added a NEWS entry.
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
I spotted this code within create_breakpoint:
if ((type_wanted != bp_breakpoint
&& type_wanted != bp_hardware_breakpoint) || thread != -1)
b->pspace = current_program_space;
this code is only executed when creating a pending breakpoint, and
sets the breakpoint::pspace member variable.
The above code gained the 'thread != -1' clause with this commit:
commit cc72b2a2da
Date: Fri Dec 23 17:06:16 2011 +0000
Introduce gdb.FinishBreakpoint in Python
While the type_wanted checks were added with this commit:
commit f8eba3c616
Date: Tue Dec 6 18:54:43 2011 +0000
the "ambiguous linespec" series
Before this breakpoint::pspace was set unconditionally.
If we look at how breakpoint::pspace is used today, some breakpoint
types specifically set this field, either in their constructors, or in
a wrapper function that calls the constructor. So, the watchpoint
type and its sub-class set this variable, as does the catchpoint type,
and all it's sub-classes.
However, code_breakpoint doesn't specifically set this field within
its constructor, though some sub-classes of
code_breakpoint (ada_catchpoint, exception_catchpoint,
internal_breakpoint, and momentary_breakpoint) do set this field.
When I examine all the places that breakpoint::pspace is used, I
believe that in every place where it is expected that this field is
set, the breakpoint type will be one that specifically sets this
field.
Next, I observe two problems with the existing code.
First, the above code is only hit for pending breakpoints, there's no
equivalent code for non-pending breakpoints. This opens up the
possibility of GDB entering non-consistent states; if a breakpoint is
first created pending and then later gets a location, the pspace field
will be set, while if the breakpoint is immediately non-pending, then
the pspace field will never be set.
Second, if we look at how breakpoint::pspace is used in the function
breakpoint_program_space_exit, we see that when a program space is
removed, any breakpoint with breakpoint::pspace set to the removed
program space, will be deleted. This makes sense, but does mean we
need to ensure breakpoint::pspace is only set for breakpoints that
apply to a single program space.
So, if I create a pending dprintf breakpoint (type bp_dprintf) then
the breakpoint::pspace variable will be set even though the dprintf is
not really tied to that one program space. As a result, when the
matching program space is removed the dprintf is incorrectly removed.
Also, if I create a thread specific breakpoint, then, thanks to the
'thread != -1' clause the wrong program space will be stored in
breakpoint::pspace (the current program space is always used, which
might not be the program space that corresponds to the selected
thread), as a result, the thread specific breakpoint will be deleted
when the matching program space is removed.
If we look at commit cc72b2a2da which added the 'thread != -1'
clause, we can see this change was entirely redundant, the
breakpoint::pspace is also set in bpfinishpy_init after
create_breakpoint has been called. As such, I think we can safely
drop the 'thread != -1' clause.
For the other problems, I'm proposing to be pretty aggressive - I'd
like to drop the breakpoint::pspace assignment completely from
create_breakpoint. Having looked at how this variable is used, I
believe that it is already set elsewhere in all the cases that it is
needed. Maybe this code was needed at one time, but I can't see how
it's needed any more.
There's tests to expose the issues I've spotted with this code, and
there's no regressions in testing.
The initial motivation for this commit was to allow thread or inferior
specific breakpoints to only be inserted within the appropriate
inferior's program-space. The benefit of this is that inferiors for
which the breakpoint does not apply will no longer need to stop, and
then resume, for such breakpoints. This commit does not make this
change, but is a refactor to allow this to happen in a later commit.
The problem we currently have is that when a thread-specific (or
inferior-specific) breakpoint is created, the thread (or inferior)
number is only parsed by calling find_condition_and_thread_for_sals.
This function is only called for non-pending breakpoints, and requires
that we know the locations at which the breakpoint will be placed (for
expression checking in case the breakpoint is also conditional).
A consequence of this is that by the time we figure out the breakpoint
is thread-specific we have already looked up locations in all program
spaces. This feels wasteful -- if we knew the thread-id earlier then
we could reduce the work GDB does by only looking up locations within
the program space for which the breakpoint applies.
Another consequence of how find_condition_and_thread_for_sals is
called is that pending breakpoints don't currently know they are
thread-specific, nor even that they are conditional! Additionally, by
delaying parsing the thread-id, pending breakpoints can be created for
non-existent threads, this is different to how non-pending
breakpoints are handled, so I can do this:
$ gdb -q ./gdb/testsuite/outputs/gdb.multi/pending-bp/pending-bp
Reading symbols from ./gdb/testsuite/outputs/gdb.multi/pending-bp/pending-bp...
(gdb) break foo thread 99
Function "foo" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (foo thread 99) pending.
(gdb) r
Starting program: /tmp/gdb/testsuite/outputs/gdb.multi/pending-bp/pending-bp
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Error in re-setting breakpoint 1: Unknown thread 99.
[Inferior 1 (process 3329749) exited normally]
(gdb)
GDB only checked the validity of 'thread 99' at the point the 'foo'
location became non-pending. In contrast, if I try this:
$ gdb -q ./gdb/testsuite/outputs/gdb.multi/pending-bp/pending-bp
Reading symbols from ./gdb/testsuite/outputs/gdb.multi/pending-bp/pending-bp...
(gdb) break main thread 99
Unknown thread 99.
(gdb)
GDB immediately checks if 'thread 99' exists. I think inconsistencies
like this are confusing, and should be fixed if possible.
In this commit the create_breakpoint function is updated so that the
extra_string, which contains the thread, inferior, task, and/or
condition information, is parsed immediately, even for pending
breakpoints.
Obviously, the condition still can't be validated until the breakpoint
becomes non-pending, but the thread, inferior, and task information
can be pulled from the extra-string, and can be validated early on,
even for pending breakpoints. The -force-condition flag is also
parsed as part of this early parsing change.
There are a couple of benefits to doing this:
1. Printing of breakpoints is more consistent now. Consider creating
a conditional breakpoint before this commit:
(gdb) set breakpoint pending on
(gdb) break pendingfunc if (0)
Function "pendingfunc" not defined.
Breakpoint 1 (pendingfunc if (0)) pending.
(gdb) break main if (0)
Breakpoint 2 at 0x401198: file /tmp/hello.c, line 18.
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y <PENDING> pendingfunc if (0)
2 breakpoint keep y 0x0000000000401198 in main at /tmp/hello.c:18
stop only if (0)
(gdb)
And after this commit:
(gdb) set breakpoint pending on
(gdb) break pendingfunc if (0)
Function "pendingfunc" not defined.
Breakpoint 1 (pendingfunc) pending.
(gdb) break main if (0)
Breakpoint 2 at 0x401198: file /home/andrew/tmp/hello.c, line 18.
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y <PENDING> pendingfunc
stop only if (0)
2 breakpoint keep y 0x0000000000401198 in main at /home/andrew/tmp/hello.c:18
stop only if (0)
(gdb)
Notice that the display of the condition is now the same for the
pending and non-pending breakpoints.
The same is true for the thread, inferior, or task information in
thread, inferior, or task specific breakpoints; this information is
displayed on its own line rather than being part of the 'What'
field.
2. We can check that the thread exists as soon as the pending
breakpoint is created. Currently there is a weird difference
between pending and non-pending breakpoints when creating a
thread-specific breakpoint.
A pending thread-specific breakpoint only checks its thread when it
becomes non-pending, at which point the thread the breakpoint was
intended for might have exited. Here's the behaviour before this
commit:
(gdb) set breakpoint pending on
(gdb) break foo thread 2
Function "foo" not defined.
Breakpoint 2 (foo thread 2) pending.
(gdb) c
Continuing.
[Thread 0x7ffff7c56700 (LWP 2948835) exited]
Error in re-setting breakpoint 2: Unknown thread 2.
[Inferior 1 (process 2948832) exited normally]
(gdb)
Notice the 'Error in re-setting breakpoint 2: Unknown thread 2.'
line, this was triggered when GDB tried to make the breakpoint
non-pending, and GDB discovers that the thread no longer exists.
Compare that to the behaviour after this commit:
(gdb) set breakpoint pending on
(gdb) break foo thread 2
Function "foo" not defined.
Breakpoint 2 (foo) pending.
(gdb) c
Continuing.
[Thread 0x7ffff7c56700 (LWP 2949243) exited]
Thread-specific breakpoint 2 deleted - thread 2 no longer in the thread list.
[Inferior 1 (process 2949240) exited normally]
(gdb)
Now the behaviour for pending breakpoints is identical to
non-pending breakpoints, the thread specific breakpoint is removed
as soon as the thread the breakpoint is associated with exits.
There is an additional change; when the pending breakpoint is
created prior to this patch we see this line:
Breakpoint 2 (foo thread 2) pending.
While after this patch we get this line:
Breakpoint 2 (foo) pending.
Notice that 'thread 2' has disappeared. This might look like a
regression, but I don't think it is. That we said 'thread 2'
before was just a consequence of the lazy parsing of the breakpoint
specification, while with this patch GDB understands, and has
parsed away the 'thread 2' bit of the spec. If folk think the old
information was useful then this would be trivial to add back in
code_breakpoint::say_where.
As a result of this commit the breakpoints 'extra_string' field is now
only used by bp_dprintf type breakpoints to hold the printf format and
arguments. This string should always be empty for other breakpoint
types. This allows some cleanup in print_breakpoint_location.
In code_breakpoint::code_breakpoint I've changed an error case into an
assert. This is because the error is now handled earlier in
create_breakpoint. As a result we know that by this point, the
extra_string will always be nullptr for anything other than a
bp_dprintf style breakpoint.
The find_condition_and_thread_for_sals function is now no longer
needed, this was previously doing the delayed splitting of the extra
string into thread, task, and condition, but this is now all done in
create_breakpoint, so find_condition_and_thread_for_sals can be
deleted, and the code that calls this in
code_breakpoint::location_spec_to_sals can be removed. With this
update this code would only ever be reached for bp_dprintf style
breakpoints, and in these cases the extra_string should not contain
anything other than format and args.
The most interesting changes are all in create_breakpoint and in the
new file break-cond-parse.c. We have a new block of code early on in
create_breakpoint that is responsible for splitting the extra_string
into its component parts by calling create_breakpoint_parse_arg_string
a function in the new break-cond-parse.c file. This means that some
of the later code can be simplified a little.
The new break-cond-parse.c file implements the splitting up the
extra_string and finding all the parts, as well as some self-tests for
the new function.
Finally, now we know all the breakpoint details, these can be stored
within the breakpoint object if we end up creating a deferred
breakpoint. Additionally, if we are creating a deferred bp_dprintf we
can parse the extra_string to build the printf command.
The implementation here aims to maintain backwards compatibility as
much as possible, this means that:
1. We support abbreviations of 'thread', 'task', and 'inferior' in
some places on the breakpoint line. The handling of abbreviations
has (before this patch) been a little weird, so this works:
(gdb) break *main th 1
And creates a breakpoint at '*main' for thread 1 only, while this
does not work:
(gdb) break main th 1
In this case GDB will try to find the symbol 'main th 1'. This
weirdness exists before and after this patch.
2. The handling of '-force-condition' is odd, if this flag appears
immediately after a condition then it will be treated as part of the
condition, e.g.:
(gdb) break main if 0 -force-condition
No symbol "force" in current context.
But we are fine with these alternatives:
(gdb) break main if 0 thread 1 -force-condition
(gdb) break main -force-condition if 0
Again, this is just a quirk of how the breakpoint line used to be
parsed, but I've maintained this for backward compatibility. During
review it was suggested that -force-condition should become an
actual breakpoint flag (i.e. only valid after the 'break' command
but before the function name), and I don't think that would be a
terrible idea, however, that's not currently a trivial change, and I
think should be done as a separate piece of work. For now, this
patch just maintains the current behaviour.
The implementation works by first splitting the breakpoint condition
string (everything after the location specification) into a list of
tokens, each token has a type and a value. (e.g. we have a THREAD
token where the value is the thread-id string). The list of tokens is
validated, and in some cases, tokens are merged. Then the values are
extracted from the remaining token list.
Consider this breakpoint command:
(gdb) break main thread 1 if argc == 2
The condition string passed to create_breakpoint_parse_arg_string is
going to be 'thread 1 if argc == 2', which is then split into the
tokens:
{ THREAD: "1" } { CONDITION: "argc == 2" }
The thread-id (1) and the condition string 'argc == 2' are extracted
from these tokens and returns back to create_breakpoint.
Now consider this breakpoint command:
(gdb) break some_function if ( some_var == thread )
Here the user wants a breakpoint if 'some_var' is equal to the
variable 'thread'. However, when this is initially parsed we will
find these tokens:
{ CONDITION: "( some_var == " } { THREAD: ")" }
This is a consequence of how we have to try and figure out the
contents of the 'if' condition without actually parsing the
expression; parsing the expression requires that we know the location
in order to lookup the variables by name, and this can't be done for
pending breakpoints (their location isn't known yet), and one of the
points of this work is that we extract things like thread-id for
pending breakpoints.
And so, it is in this case that token merging takes place. We check
if the value of a token appearing immediately after the CONDITION
token looks valid. In this case, does ')' look like a valid
thread-id. Clearly, in this case ')' does not, and so me merge the
THREAD token into the condition token, giving:
{ CONDITION: "( some_var == thread )" }
Which is what we want.
I'm sure that we might still be able to come up with some edge cases
where the parser makes the wrong choice. I think long term the best
way to work around these would be to move the thread, inferior, task,
and -force-condition flags to be "real" command options for the break
command. I am looking into doing this, but can't guarantee if/when
that work would be completed, so this patch should be reviewed assume
that the work will never arrive (though I hope it will).
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
This commit makes breakpoint_debug_printf available outside of
breakpoint.c. In a later commit I'll want to use this macro from
another file.
This is just a refactor, there should be no user visible changes after
this commit.
Following on from the previous commit, this commit marks the old
unquoted filename completion related functions as deprecated.
The aim of doing this is to make it more obvious to someone adding a
new command that they should not be using the older unquoted style
filename argument handling.
I split this change from the previous to make for an easier review.
This commit touches more files, but is _just_ function renaming.
Check out gdb/completer.{c,h} for what has been renamed. All the
other files have just been updated to use the new names.
There should be no user visible changes after this commit.
It is possible to attach a condition to a catchpoint. This can't be
done when the catchpoint is created, but can be done with the
'condition' command, this is documented in the GDB manual:
You can also use the 'if' keyword with the 'watch' command. The
'catch' command does not recognize the 'if' keyword; 'condition' is the
only way to impose a further condition on a catchpoint.
A GDB crash was reported against Fedora GDB where a user had attached
a condition to a catchpoint and then restarted the inferior. When the
catchpoint was hit GDB would immediately segfault. I was able to
reproduce the failure on upstream GDB:
(gdb) file ./some/binary
(gdb) catch syscall write
(gdb) run
...
Catchpoint 1 (returned from syscall write), 0x00007ffff7b594a7 in write () from /lib64/libc.so.6
(gdb) condition 1 $_streq((char *) $rsi, "foobar") == 0
(gdb) run
...
Fatal signal: Segmentation fault
...
What happened here is that on the system in question we had debug
information available for both the main application and also for
libc.
When the condition was attached GDB was stopped inside libc and as the
debug information was available GDB found a reference to the 'char'
type (for the cast) inside libc's debug information.
When the inferior is restarted GDB discards all of the objfiles
associated with shared libraries, and this includes libc. As such the
'char' type, which is objfile owned, is discarded and the reference to
it from the catchpoint's condition expression becomes invalid.
Now, if it were a breakpoint instead of a catchpoint, what would
happen is that after the shared library objfiles had been discarded
we'd call the virtual breakpoint::re_set method on the breakpoint, and
this would update the breakpoint's condition expression. This is
because user breakpoints are actually instances of the code_breakpoint
class and the code_breakpoint::re_set method contains the code to
recompute the breakpoint's condition expression.
However, catchpoints are instances of the catchpoint class which
inherits from the base breakpoint class. The catchpoint class does
not override breakpoint::re_set, and breakpoint::re_set is empty!
The consequence of this is that catchpoint condition expressions are
never recomputed, and the dangling pointer to the now deleted, objfile
owned type 'char' is left around, and, when the catchpoint is hit, the
invalid pointer is used when GDB tries to evaluate the condition
expression.
In this commit I have implemented catchpoint::re_set. This is pretty
simple and just recomputes the condition expression as you'd expect.
If the condition doesn't evaluate then the catchpoint is marked as
disabled_by_cond.
I have also made breakpoint::re_set pure virtual. With the addition
of catchpoint::re_set every sub-class of breakpoint now implements the
::re_set method, and if new sub-classes are added in the future I
think that they _must_ implement ::re_set in order to avoid this
problem. As such falling back to an empty breakpoint::re_set doesn't
seem helpful.
For testing I have not relied on stopping in libc and having libc
debug information available, this doesn't seem like a good idea for
the GDB testsuite. Instead I create a (rather pointless) condition
check that uses a type defined only within a shared library. When the
inferior is restarted the catchpoint will temporarily be marked as
disabled_by_cond (due to the type not being available), but once the
shared library is loaded again the catchpoint will be re-enabled.
Without the fixes above then the same crashing behaviour can be
observed.
One point of note: the dangling pointer of course exposes undefined
behaviour, with no guarantee of a crash. Though a crash is what I
usually see I have see GDB throw random errors from the expression
evaluation code, and once, I saw no problem at all! If you recompile
GDB with the address sanitizer, or run under valgrind, then the bug
will be exposed every time.
After fixing this bug I checked bugzilla and found PR gdb/29960 which
is the same bug. I was able to reproduce the bug before this commit,
and after this commit GDB is no longer crashing.
Before:
(gdb) file /tmp/hello.x
Reading symbols from /tmp/hello.x...
(gdb) run
Starting program: /tmp/hello.x
Hello World
[Inferior 1 (process 1101855) exited normally]
(gdb) catch syscall 1
Catchpoint 1 (syscall 'write' [1])
(gdb) condition 1 write.fd == 1
(gdb) run
Starting program: /tmp/hello.x
Fatal signal: Segmentation fault
...
And after:
(gdb) file /tmp/hello.x
Reading symbols from /tmp/hello.x...
(gdb) run
Starting program: /tmp/hello.x
Hello World
Args: ( 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 )
[Inferior 1 (process 1102373) exited normally]
(gdb) catch syscall 1
Catchpoint 1 (syscall 'write' [1])
(gdb) condition 1 write.fd == 1
(gdb) r
Starting program: /tmp/hello.x
Error in testing condition for breakpoint 1:
Attempt to extract a component of a value that is not a structure.
Catchpoint 1 (call to syscall write), 0x00007ffff7eb94a7 in write ()
from /lib64/libc.so.6
(gdb) ptype write
type = <unknown return type> ()
(gdb)
Notice we get the error now when the condition fails to evaluate.
This seems reasonable given that 'write' will be a function, and
indeed the final 'ptype' shows that it's a function, not a struct.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29960
Reviewed-By: Tom de Vries <tdevries@suse.de>
I spotted that we have a duplicate condition check in the function
disable_breakpoints_in_freed_objfile.
Lets remove it.
There should be no user visible changes after this commit.
Approved-By: Tom Tromey <tom@tromey.com>
While working on something else, I noticed that this is relatively
common:
scoped_restore_current_language save;
set_language (something);
This patch adds a second constructor to
scoped_restore_current_language to simplify this idiom.
Reviewed-By: Tom de Vries <tdevries@suse.de>
A DAP user noticed that breakpoints set by address were never updated
to show their location after the DAP launch request. It turns out
that gdb does not emit the breakpoint-modified event when this sort of
breakpoint is updated.
This patch changes gdb to notify the breakpoint-modified observer when
a breakpoint location's symbol changes. This in turn causes the DAP
event to be emitted.
Reviewed-by: Keith Seitz <keiths@redhat.com>
Make the current program space reference bubble up one level. Use a
program space from the context whenever that makes sense.
Change-Id: Id3b0bf4490178d71a9aecdbf404b9287c22b30f5
Reviewed-by: Keith Seitz <keiths@redhat.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>
>From what I can see, lookup_minimal_symbol doesn't have any dependencies
on the global current state other than the single reference to
current_program_space. Add a program_space parameter and make that
current_program_space reference bubble up one level.
Change-Id: I759415e2f9c74c9627a2fe05bd44eb4147eee6fe
Reviewed-by: Keith Seitz <keiths@redhat.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>
Most calls to lookup_minimal_symbol don't pass a value for sfile and
objf. Make these parameters optional (have a default value of
nullptr). And since passing a value to `objf` is much more common than
passing a value to `sfile`, swap the order so `objf` comes first, to
avoid having to pass a nullptr value to `sfile` when wanting to pass a
value to `objf`.
Change-Id: I8e9cc6b942e593bec640f9dfd30f62786b0f5a27
Reviewed-by: Keith Seitz <keiths@redhat.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>
This is a simple find / replace from "struct bound_minimal_symbol" to
"bound_minimal_symbol", to make things shorter and more consisten
througout. In some cases, move variable declarations where first used.
Change-Id: Ica4af11c4ac528aa842bfa49a7afe8fe77a66849
Reviewed-by: Keith Seitz <keiths@redhat.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>
The tracepoint_probe_create_sals_from_location_spec function just
forwards all its arguments to
bkpt_probe_create_sals_from_location_spec, and is only used in one
place.
Lets delete tracepoint_probe_create_sals_from_location_spec and
replace it with bkpt_probe_create_sals_from_location_spec.
There should be no user visible changes after this commit.
During a later patch I wanted to reset a single breakpoint, so I
called breakpoint_re_set_one. However, this is not the right thing to
do. If we look at breakpoint_re_set then we see that there's a whole
bunch of state that needs to be preserved prior to calling
breakpoint_re_set_one, and after calling breakpoint_re_set_one we
still need to call update_global_location_list.
I could just update the comment on breakpoint_re_set_one to make it
clearer how the function should be used -- or more likely to warn that
the function should only be used as a helper from breakpoint_re_set.
However, breakpoint_re_set_one is only 3 lines long. So I figure it
might actually be easier to just fold breakpoint_re_set_one into
breakpoint_re_set, then there's no risk of accidentally calling
breakpoint_re_set_one when we shouldn't.
There should be no user visible changes after this commit.
I noticed that in the 'info breakpoints' output, GDB sometimes prints
the inferior list for pending breakpoints, this doesn't seem right to
me. A pending breakpoint has no locations (at least, as far as we
display things in the 'info breakpoints' output), so including an
inferior list seems odd.
Here's what I see right now:
(gdb) info breakpoint 5
Num Type Disp Enb Address What
5 breakpoint keep y <PENDING> foo inf 1
(gdb)
It's the 'inf 1' at the end of the line that I'm objecting too.
To trigger this behaviour we need to be in a multi-inferior debug
session. The breakpoint must have been non-pending at some point in
the past, and so have a location assigned to it.
The breakpoint becomes pending again as a result of a shared library
being unloaded. When this happens the location itself is marked
pending (via bp_location::shlib_disabled).
In print_one_breakpoint_location, in order to print the inferior list
we check that the breakpoint has a location, and that we have multiple
inferiors, but we don't check if the location itself is pending.
This commit adds that check, which means the output is now:
(gdb) info breakpoint 5
Num Type Disp Enb Address What
5 breakpoint keep y <PENDING> foo
(gdb)
Which I think makes more sense -- indeed, the format without the
inferior list is what we display for a pending breakpoint that has
never had any locations assigned, so I think this change in behaviour
makes GDB more consistent.
Make the current program space reference bubble up one level.
Change-Id: I6ba6dc4a2cb188720cbb61b84ab5c954aac105c6
Approved-By: Tom Tromey <tom@tromey.com>
Reviewed-By: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
It is obvious that pspace is the same as current_program_space in these
cases, due to the set_current_program_space call just above. The rest
of the functions probably care about the current program space though,
so leave the set_cset_current_program_space calls there.
Change-Id: I3c300decbf2c2fe5f25aa7f697ebcb524432394f
Remove some includes reported as unused by clangd. Add some includes in
other files that were previously relying on the transitive include.
Change-Id: Ibdd0a998b04d21362a20d0ca8e5267e21e2e133e
This patch changes the docstring self-test to verify that there is no
trailing whitespace at the end of lines. A few existing docstrings
had to be updated.
Most files including gdbcmd.h currently rely on it to access things
actually declared in cli/cli-cmds.h (setlist, showlist, etc). To make
things easy, replace all includes of gdbcmd.h with includes of
cli/cli-cmds.h. This might lead to some unused includes of
cli/cli-cmds.h, but it's harmless, and much faster than going through
the 170 or so files by hand.
Change-Id: I11f884d4d616c12c05f395c98bbc2892950fb00f
Approved-By: Tom Tromey <tom@tromey.com>
Move some declarations related to the "quit" machinery from defs.h to
event-top.h. Most of the definitions associated to these declarations
are in event-top.c. The exceptions are `quit()` and `maybe_quit()`,
that are defined in utils.c. For consistency, move these two
definitions to event-top.c.
Include "event-top.h" in many files that use these things.
Change-Id: I6594f6df9047a9a480e7b9934275d186afb14378
Approved-By: Tom Tromey <tom@tromey.com>
Currently, when the current thread is running, you can print global
variables. However, if you try to set a watchpoint on the same
globals, GDB errors out, complaining that the selected thread is
running. Like so:
(gdb) c&
Continuing.
(gdb) p global
$1 = 1098377287
(gdb) watch global
Selected thread is running.
This patch makes setting the watchpoint work. You'll now get:
(gdb) c&
Continuing.
(gdb) [New Thread 0x7ffff7d6e640 (LWP 434993)]
[New Thread 0x7ffff756d640 (LWP 434994)]
p global
$1 = 88168
(gdb) watch global
Hardware watchpoint 2: global
(gdb) [Switching to Thread 0x7ffff7d6e640 (LWP 434993)]
Thread 2 "function0" hit Hardware watchpoint 2: global
Old value = 185420
New value = 185423
int_return () at threads.c:39
39 }
The problem is that update_watchpoint calls get_selected_frame
unconditionally. We can skip it if the watchpoint expression is only
watching globals.
This adds a testcase that exercises both all-stop and non-stop, and
also software and hardware watchpoints. It is kfailed for software
watchpoints, as those require another fix not handled by this patch
(the sw watchpoint doesn't fire because GDB doesn't force the
running-free thread to switch to single-stepping).
Change-Id: I68ca948541aea3edd4f70741f272f543187abe40
