[Bug external/8841] Can not set breakpoints in the vsyscall page

[Bug external/8841] Can not set breakpoints in the vsyscall page

[kalvdans at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=8841

chn <kalvdans at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kalvdans at gmail dot com

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[Bug external/8841] Can not set breakpoints in the vsyscall page

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=8841

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jan.kratochvil at redhat
                   |                            |dot com

--- Comment #2 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2012-03-04 08:09:03 UTC ---
This works for any recent Linux kernels (2.6+).

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[Bug external/8841] Can not set breakpoints in the vsyscall page

[kalvdans at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=8841

--- Comment #3 from chn <kalvdans at gmail dot com> 2012-03-04 20:08:53 UTC ---
It does not work on my Fedora 16 system, Linux 3.2:

chn@jaz:~$ uname -r
3.2.7-1.fc16.x86_64
chn@jaz:~$ gdb /bin/ls
GNU gdb (GDB) Fedora (7.3.50.20110722-10.fc16)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /bin/ls...(no debugging symbols found)...done.
Missing separate debuginfos, use: debuginfo-install
coreutils-8.12-6.fc16.x86_64
(gdb) break *0xffffffffff600000
Breakpoint 1 at 0xffffffffff600000
(gdb) r
Starting program: /bin/ls 
Warning:
Cannot insert breakpoint 1.
Error accessing memory address 0xffffffffff600000: Input/output error.
(gdb) 

Strace of gdb shows that it fails to insert the 0xcc int3 opcode on the
vsyscall page:

ptrace(PTRACE_GETREGS, 26776, 0, 0x7fff9d80cdf0) = 0
ptrace(PTRACE_SETREGS, 26776, 0, 0x7fff9d80cdf0) = 0
ptrace(PTRACE_PEEKTEXT, 26776, 0x3f65e0f990, [0x2e6666666666c3f3]) = 0
ptrace(PTRACE_PEEKTEXT, 26776, 0x3f65e0f990, [0x2e6666666666c3f3]) = 0
ptrace(PTRACE_POKEDATA, 26776, 0x3f65e0f990, 0x2e6666666666c3cc) = 0
ptrace(PTRACE_PEEKTEXT, 26776, 0xffffffffff600000, [0xf00000060c0c748]) = 0
ptrace(PTRACE_PEEKTEXT, 26776, 0xffffffffff600000, [0xf00000060c0c748]) = 0
ptrace(PTRACE_POKEDATA, 26776, 0xffffffffff600000, 0xf00000060c0c7cc) = -1 EIO
(Input/output error)
ptrace(PTRACE_POKETEXT, 26776, 0xffffffffff600000, 0xf00000060c0c7cc) = -1 EIO
(Input/output error)

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[Bug external/8841] Can not set breakpoints in the vsyscall page

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=8841

--- Comment #4 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2012-03-04 20:34:39 UTC ---
OK, confirming, it works for [vdso] for me but not for [vsyscall].
Even 'hbreak' does not work which is suspicious.

(gdb) hbreak *0xffffffffff600000
Hardware assisted breakpoint 2 at 0xffffffffff600000
(gdb) c
Continuing.
Couldn't write debug register: Invalid argument.

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[Bug external/8841] Can not set breakpoints in the vsyscall page

[sandra at codesourcery dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=8841

sandra at codesourcery dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sandra at codesourcery dot com

--- Comment #5 from sandra at codesourcery dot com ---
nios2-*-linux* has similar problems (kernel versions 3.19 and later).  The
kernel creates a signal trampoline at address 0x1044 that GDB cannot write to
to set a software breakpoint.

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[Bug external/8841] Can not set breakpoints in the vsyscall page

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=8841

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
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                 CC|                            |ssbssa at sourceware dot org

--- 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>:
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;
> h=7eb895307f53af3435440d3fe67c0e4e679d99b2
> 
> commit 7eb895307f53af3435440d3fe67c0e4e679d99b2
> Author: Yao Qi <yao.qi@arm.com>
> Date:   Mon May 23 17:32:56 2016 +0100
> 
>     Skip unwritable frames in command "finish"
>     
>     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,
>     
>      (gdb) bt
>      #0  CT32B1_IRQHandler () at ../src/timer.c:67
>      #1  <signal handler called>
>      #2  main () at ../src/timer.c:127
>     
>     (gdb) info frame
>     Stack level 0, frame at 0x200ffa8:
>      pc = 0x4ec in CT32B1_IRQHandler (../src/timer.c:67); saved pc =
> 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
>     
>     (gdb) x/x 0xfffffff9
>     0xfffffff9:     Cannot access memory at address 0xfffffff9
>     
>     (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?)
>     
>     Warning:
>     Cannot insert hardware breakpoint 0.
>     Could not insert hardware breakpoints:
>     You may have requested too many hardware breakpoints/watchpoints.
>     
>     Command aborted.
>     
>     even some debug probe can't set hardware breakpoint on the magic
>     address too,
>     
>     (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?)
>     
>     Warning:
>     Cannot insert hardware breakpoint 2.
>     Could not insert hardware breakpoints:
>     You may have requested too many hardware breakpoints/watchpoints.
>     
>     Command aborted.
>     
>     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?

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[Bug external/8841] Can not set breakpoints in the vsyscall page

[sandra.oss at frogsonice dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=8841

--- Comment #8 from Sandra Loosemore <sandra.oss at frogsonice dot com> ---
I no longer have access to nios2 test hardware to confirm this has been fixed
on that target.  Intel has EOL'ed the architecture now so you should just
ignore it if this is now working on other affected targets.

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