forked from Imagelibrary/binutils-gdb
8cdf110a11
On aarch64-linux, in test-case gdb.base/nostdlib.exp I run into:
...
(gdb) continue^M
Continuing.^M
warning: Temporarily disabling breakpoints for unloaded shared library \
"/lib/ld-linux-aarch64.so.1"^M
^M
Breakpoint 2, _start () at nostdlib.c:20^M
20 {^M
(gdb) FAIL: $exp: pie=pie: continue to marker
...
This happens as follows:
- the test-case sets a breakpoint on *_start,
- the breakpoint resolves to *_start in the executable,
- the executable is started, and the breakpoint resolves to *_start in the
dynamic linker,
- execution stops at *_start in the dynamic linker,
- the test-case issues a continue, expecting to continue to the breakpoint on
marker,
- while continuing, the dynamic linker is reported as unloaded,
- the breakpoint again resolves to *_start in the executable,
- execution stops at *_start in the executable, and
- the test-case concludes that it failed to "continue to marker".
This doesn't happen on x86_64-linux. There, after the executable is started,
the breakpoint again resolves to *_start in the exec.
This is similar to what happens when printing _start.
On aarch64-linux, we print the _start in the dynamic linker:
...
$ gdb -q -batch outputs/gdb.base/nostdlib/nostdlib-pie \
-ex "b _start" \
-ex run \
-ex "print _start" \
-ex "info break"
Breakpoint 1 at 0x2bc: file nostdlib.c, line 23.
Breakpoint 1.2, _start () at ../sysdeps/aarch64/dl-start.S:22
22 ENTRY (_start)
$1 = {void (void)} 0xfffff7fd6ac0 <_start>
Num Type Disp Enb Address What
1 breakpoint keep y <MULTIPLE>
breakpoint already hit 1 time
1.1 y 0x0000aaaaaaaa02bc in _start at nostdlib.c:23
1.2 y 0x0000fffff7fd6ac0 in _start at dl-start.S:22
...
On x86_64-linux, we print the _start in the exec:
...
Breakpoint 1 at 0x2c5: file nostdlib.c, line 23.
Breakpoint 1.2, 0x00007ffff7fe4f00 in _start () from \
/lib64/ld-linux-x86-64.so.2
$1 = {void (void)} 0x5555555542c1 <_start>
Num Type Disp Enb Address What
1 breakpoint keep y <MULTIPLE>
breakpoint already hit 1 time
1.1 y 0x00005555555542c5 in _start at nostdlib.c:23
1.2 y 0x00007ffff7fe4f00 <_start>
...
The difference may be down to the availability of debug info for the _start in
the dynamic linker.
Finally, the described scenario on aarch64-linux is not deterministic. The
behavior depends on the dynamic linker being reported as unloaded, which has
been classified as a GLIBC bug, so that might get fixed.
Ideally this test-case would stop at both *_start in the executable and the
dynamic linker, but in absense of a way to specify this reliably (see PR32748),
fix this by making this a temporary breakpoint, ensuring that the breakpoint
will only trigger once.
Approved-by: Kevin Buettner <kevinb@redhat.com>
PR testsuite/32743
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32743
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