Files
binutils-gdb/gdb/observable.h
Andrew Burgess 9da3b73547 gdb: include a still-mapped flag in solib unload notification
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.
2025-02-09 17:38:11 +00:00

264 lines
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C++

/* Observers
Copyright (C) 2016-2024 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef GDB_OBSERVABLE_H
#define GDB_OBSERVABLE_H
#include "gdbsupport/observable.h"
#include "target/waitstatus.h"
struct bpstat;
struct solib;
struct objfile;
struct thread_info;
struct inferior;
struct process_stratum_target;
struct target_ops;
struct trace_state_variable;
struct program_space;
namespace gdb
{
namespace observers
{
/* The inferior has stopped for real. The BS argument describes the
breakpoints were are stopped at, if any. Second argument
PRINT_FRAME non-zero means display the location where the
inferior has stopped.
gdb notifies all normal_stop observers when the inferior execution
has just stopped, the associated messages and annotations have been
printed, and the control is about to be returned to the user.
Note that the normal_stop notification is not emitted when the
execution stops due to a breakpoint, and this breakpoint has a
condition that is not met. If the breakpoint has any associated
commands list, the commands are executed after the notification is
emitted. */
extern observable<struct bpstat */* bs */, int /* print_frame */> normal_stop;
/* The inferior was stopped by a signal. */
extern observable<enum gdb_signal /* siggnal */> signal_received;
/* The target's register contents have changed. */
extern observable<struct target_ops */* target */> target_changed;
/* The executable being debugged by GDB in PSPACE has changed: The user
decided to debug a different program, or the program he was debugging
has been modified since being loaded by the debugger (by being
recompiled, for instance). The path to the new executable can be found
by examining PSPACE->exec_filename.
When RELOAD is true the path to the executable hasn't changed, but the
file does appear to have changed, so GDB reloaded it, e.g. if the user
recompiled the executable. when RELOAD is false then the path to the
executable has not changed. */
extern observable<struct program_space */* pspace */,
bool /*reload */> executable_changed;
/* gdb has just connected to an inferior. For 'run', gdb calls this
observer while the inferior is still stopped at the entry-point
instruction. For 'attach' and 'core', gdb calls this observer
immediately after connecting to the inferior, and before any
information on the inferior has been printed. */
extern observable<inferior */* inferior */> inferior_created;
/* The inferior EXEC_INF has exec'ed a new executable file.
Execution continues in FOLLOW_INF, which may or may not be the same as
EXEC_INF, depending on "set follow-exec-mode". */
extern observable<inferior */* exec_inf */, inferior */* follow_inf */>
inferior_execd;
/* The inferior PARENT_INF has forked. If we are setting up an inferior for
the child (because we follow only the child or we follow both), CHILD_INF
is the child inferior. Otherwise, CHILD_INF is nullptr.
FORK_KIND is TARGET_WAITKIND_FORKED or TARGET_WAITKIND_VFORKED. */
extern observable<inferior */* parent_inf */, inferior */* child_inf */,
target_waitkind /* fork_kind */> inferior_forked;
/* The shared library specified by SOLIB has been loaded. Note that
when gdb calls this observer, the library's symbols probably
haven't been loaded yet. */
extern observable<solib &/* solib */> solib_loaded;
/* The shared library SOLIB has been unloaded from program space PSPACE.
Note when gdb calls this observer, the library's symbols have not
been unloaded yet, and thus are still available. */
extern observable<program_space *, const solib &/* solib */,
bool /* still_in_use */> solib_unloaded;
/* The symbol file specified by OBJFILE has been loaded. */
extern observable<struct objfile */* objfile */> new_objfile;
/* All objfiles from PSPACE were removed. */
extern observable<program_space */* pspace */> all_objfiles_removed;
/* The object file specified by OBJFILE is about to be freed. */
extern observable<struct objfile */* objfile */> free_objfile;
/* The thread specified by T has been created. */
extern observable<struct thread_info */* t */> new_thread;
/* The thread specified by T has exited. EXIT_CODE is the thread's
exit code, if available. The SILENT argument indicates that GDB is
removing the thread from its tables without wanting to notify the
CLI about it. */
extern observable<thread_info */* t */,
std::optional<ULONGEST> /* exit_code */,
bool /* silent */> thread_exit;
/* The thread specified by T has been deleted, with delete_thread.
This is called just before the thread_info object is destroyed with
operator delete. */
extern observable<thread_info */* t */> thread_deleted;
/* An explicit stop request was issued to PTID. If PTID equals
minus_one_ptid, the request applied to all threads. If
ptid_is_pid(PTID) returns true, the request applied to all
threads of the process pointed at by PTID. Otherwise, the
request applied to the single thread pointed at by PTID. */
extern observable<ptid_t /* ptid */> thread_stop_requested;
/* The target was resumed. The PTID parameter specifies which
thread was resume, and may be RESUME_ALL if all threads are
resumed. */
extern observable<ptid_t /* ptid */> target_resumed;
/* The target is about to be proceeded. */
extern observable<> about_to_proceed;
/* A new breakpoint B has been created. */
extern observable<struct breakpoint */* b */> breakpoint_created;
/* A breakpoint has been destroyed. The argument B is the
pointer to the destroyed breakpoint. */
extern observable<struct breakpoint */* b */> breakpoint_deleted;
/* A breakpoint has been modified in some way. The argument B
is the modified breakpoint. */
extern observable<struct breakpoint */* b */> breakpoint_modified;
/* GDB has instantiated a new architecture, NEWARCH is a pointer to the new
architecture. */
extern observable<struct gdbarch */* newarch */> new_architecture;
/* The thread's ptid has changed. The OLD_PTID parameter specifies
the old value, and NEW_PTID specifies the new value. */
extern observable<process_stratum_target * /* target */,
ptid_t /* old_ptid */, ptid_t /* new_ptid */>
thread_ptid_changed;
/* The inferior INF has been added to the list of inferiors. At
this point, it might not be associated with any process. */
extern observable<struct inferior */* inf */> inferior_added;
/* The inferior identified by INF has been attached to a
process. */
extern observable<struct inferior */* inf */> inferior_appeared;
/* Inferior INF is about to be detached. */
extern observable<struct inferior */* inf */> inferior_pre_detach;
/* Either the inferior associated with INF has been detached from
the process, or the process has exited. */
extern observable<struct inferior */* inf */> inferior_exit;
/* The inferior INF has been removed from the list of inferiors.
This method is called immediately before freeing INF. */
extern observable<struct inferior */* inf */> inferior_removed;
/* The inferior CLONE has been created by cloning INF. */
extern observable<struct inferior */* inf */, struct inferior */* clone */>
inferior_cloned;
/* Bytes from DATA to DATA + LEN have been written to the inferior
at ADDR. */
extern observable<struct inferior */* inferior */, CORE_ADDR /* addr */,
ssize_t /* len */, const bfd_byte */* data */>
memory_changed;
/* Called before a top-level prompt is displayed. CURRENT_PROMPT is
the current top-level prompt. */
extern observable<const char */* current_prompt */> before_prompt;
/* Variable gdb_datadir has been set. The value may not necessarily
change. */
extern observable<> gdb_datadir_changed;
/* An inferior function at ADDRESS is about to be called in thread
THREAD. */
extern observable<ptid_t /* thread */, CORE_ADDR /* address */>
inferior_call_pre;
/* The inferior function at ADDRESS has just been called. This
observer is called even if the inferior exits during the call.
THREAD is the thread in which the function was called, which may
be different from the current thread. */
extern observable<ptid_t /* thread */, CORE_ADDR /* address */>
inferior_call_post;
/* A register in the inferior has been modified by the gdb user. */
extern observable<const frame_info_ptr &/* frame */, int /* regnum */>
register_changed;
/* The user-selected inferior, thread and/or frame has changed. The
user_select_what flag specifies if the inferior, thread and/or
frame has changed. */
extern observable<user_selected_what /* selection */>
user_selected_context_changed;
/* This is notified when a styling setting has changed, content may need
to be updated based on the new settings. */
extern observable<> styling_changed;
/* The CLI's notion of the current source has changed. This differs
from user_selected_context_changed in that it is also set by the
"list" command. */
extern observable<> current_source_symtab_and_line_changed;
/* Called when GDB is about to exit. */
extern observable<int> gdb_exiting;
/* When a connection is removed. */
extern observable<process_stratum_target */* target */> connection_removed;
/* About to enter target_wait (). */
extern observable <ptid_t /* ptid */> target_pre_wait;
/* About to leave target_wait (). */
extern observable <ptid_t /* event_ptid */> target_post_wait;
/* New program space PSPACE was created. */
extern observable <program_space */* pspace */> new_program_space;
/* The program space PSPACE is about to be deleted. */
extern observable <program_space */* pspace */> free_program_space;
extern observable<bool /* enabled */> tui_enabled;
} /* namespace observers */
} /* namespace gdb */
#endif /* GDB_OBSERVABLE_H */