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From: "ssbssa at sourceware dot org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug external/8841] Can not set breakpoints in the vsyscall page
Date: Sun, 14 Jan 2024 14:31:20 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D8841

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at sourceware dot o=
rg

--- Comment #7 from Hannes Domani <ssbssa at sourceware dot org> ---
(In reply to Sourceware Commits from comment #6)
> The master branch has been updated by Yao Qi <qiyao@sourceware.org>:
>=20
> https://sourceware.org/git/gitweb.cgi?p=3Dbinutils-gdb.git;
> h=3D7eb895307f53af3435440d3fe67c0e4e679d99b2
>=20
> commit 7eb895307f53af3435440d3fe67c0e4e679d99b2
> Author: Yao Qi <yao.qi@arm.com>
> Date:   Mon May 23 17:32:56 2016 +0100
>=20
>     Skip unwritable frames in command "finish"
>=20=20=20=20=20
>     Nowadays, GDB can't insert breakpoint on the return address of the
>     exception handler on ARM M-profile, because the address is a magic
>     one 0xfffffff9,
>=20=20=20=20=20
>      (gdb) bt
>      #0  CT32B1_IRQHandler () at ../src/timer.c:67
>      #1  <signal handler called>
>      #2  main () at ../src/timer.c:127
>=20=20=20=20=20
>     (gdb) info frame
>     Stack level 0, frame at 0x200ffa8:
>      pc =3D 0x4ec in CT32B1_IRQHandler (../src/timer.c:67); saved pc =3D
> 0xfffffff9
>      called by frame at 0x200ffc8
>      source language c.
>      Arglist at 0x200ffa0, args:
>      Locals at 0x200ffa0, Previous frame's sp is 0x200ffa8
>      Saved registers:
>       r7 at 0x200ffa0, lr at 0x200ffa4
>=20=20=20=20=20
>     (gdb) x/x 0xfffffff9
>     0xfffffff9:     Cannot access memory at address 0xfffffff9
>=20=20=20=20=20
>     (gdb) finish
>     Run till exit from #0  CT32B1_IRQHandler () at ../src/timer.c:67
>     Ed:15: Target error from Set break/watch: Et:96: Pseudo-address
> (0xFFFFFFxx) for EXC_RETURN is invalid (GDB error?)
>=20=20=20=20=20
>     Warning:
>     Cannot insert hardware breakpoint 0.
>     Could not insert hardware breakpoints:
>     You may have requested too many hardware breakpoints/watchpoints.
>=20=20=20=20=20
>     Command aborted.
>=20=20=20=20=20
>     even some debug probe can't set hardware breakpoint on the magic
>     address too,
>=20=20=20=20=20
>     (gdb) hbreak *0xfffffff9
>     Hardware assisted breakpoint 2 at 0xfffffff9
>     (gdb) c
>     Continuing.
>     Ed:15: Target error from Set break/watch: Et:96: Pseudo-address
> (0xFFFFFFxx) for EXC_RETURN is invalid (GDB error?)
>=20=20=20=20=20
>     Warning:
>     Cannot insert hardware breakpoint 2.
>     Could not insert hardware breakpoints:
>     You may have requested too many hardware breakpoints/watchpoints.
>=20=20=20=20=20
>     Command aborted.
>=20=20=20=20=20
>     The problem described above is quite similar to PR 8841, in which GDB
>     can't set breakpoint on signal trampoline, which is mapped to a read-=
only
>     page by kernel.  The rationale of this patch is to skip "unwritable"
>     frames when looking for caller frames in command "finish", and a new
>     gdbarch method code_of_frame_writable is added.  This patch fixes
>     the problem on ARM cortex-m target, but it can be used to fix
>     PR 8841 too.

Can this be closed?

--=20
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