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

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

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

--- Comment #6 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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.

    gdb:

    2016-05-10  Yao Qi  <yao.qi@arm.com>

        * arch-utils.c (default_code_of_frame_writable): New function.
        * arch-utils.h (default_code_of_frame_writable): Declare.
        * arm-tdep.c (arm_code_of_frame_writable): New function.
        (arm_gdbarch_init): Install gdbarch method
        code_of_frame_writable if the target is M-profile.
        * frame.c (skip_unwritable_frames): New function.
        * frame.h (skip_unwritable_frames): Declare.
        * gdbarch.sh (code_of_frame_writable): New.
        * gdbarch.c, gdbarch.h: Re-generated.
        * infcmd.c (finish_command): Call skip_unwritable_frames.

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