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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug breakpoints/27205] [-m32] FAIL: gdb.base/longjmp.exp: next over
 longjmp(1)
Date: Sat, 23 Jan 2021 06:38:40 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D27205

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
The failure to access memory is due to glibc having pointer encryption (aka
"pointer mangling" or "pointer guard") of the long jump buffer.

So, when we're trying to read pc from the long jump buffer in
i386_get_longjmp_target, we get an encrypted pointer, and don't decrypt it.=
=20
This issue has been known for a bit, see
https://sourceware.org/legacy-ml/gdb-patches/2008-04/msg00127.html.

Possibly error mode could be improved: if we can detect that pc is not in a
text segment or displaced stepping buffer, we return 0 in
i386_get_longjmp_target, and revert to single stepping.

Anyway, the reason we're exercising i386_get_longjmp_target is that this fa=
ils:
...

          /* If we set the longjmp breakpoint via a SystemTap probe,=20=20=
=20=20=20=20=20=20=20=20=20=20
             then use it to extract the arguments.  The destination PC=20=
=20=20=20=20=20=20=20=20=20
             is the third argument to the probe.  */
          arg_value =3D probe_safe_evaluate_at_pc (frame, 2);
...
I double checked on openSUSE Leap 15.2 and there this works, so I'll try to
figure out what's the difference.

--=20
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