[Bug tdep/31705] gdb.base/watchpoint-running.exp fails on arm

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

https://sourceware.org/bugzilla/show_bug.cgi?id=31705

--- Comment #20 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The gdb-15-branch branch has been updated by Tom de Vries
<vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f33b87956ffa9d153d39caf625b35f29597f0326

commit f33b87956ffa9d153d39caf625b35f29597f0326
Author: Pedro Alves <pedro@palves.net>
Date:   Fri Jun 21 16:46:50 2024 +0200

    [gdb/tdep] Fix gdb.base/watchpoint-running.exp on {arm,ppc64le}-linux

    When running test-case gdb.base/watchpoint-running on ppc64le-linux (and
    similar on arm-linux), we get:
    ...
    (gdb) watch global_var^M
    warning: Error when detecting the debug register interface. \
      Debug registers will be unavailable.^M
    Watchpoint 2: global_var^M
    (gdb) FAIL: $exp: all-stop: hardware: watch global_var
    FAIL: $exp: all-stop: hardware: watchpoint hit (timeout)
    ...

    The problem is that ppc_linux_dreg_interface::detect fails to detect the
    hardware watchpoint interface, because the calls to ptrace return with
errno
    set to ESRCH.

    This is a feature of ptrace: if a call is done while the tracee is not
    ptrace-stopped, it returns ESRCH.

    Indeed, in the test-case "watch global_var" is executed while the inferior
is
    running, and that triggers the first call to
ppc_linux_dreg_interface::detect.

    And because the detection failure is cached, subsequent attempts at setting
    hardware watchpoints will also fail, even if the tracee is ptrace-stopped.

    The way to fix this is to make sure that ppc_linux_dreg_interface::detect
is
    called when we know that the thread is ptrace-stopped, which in the current
    setup is best addressed by using target-specific post_attach and
    post_startup_inferior overrides.  However, as we can see in
    aarch64_linux_nat_target, that causes code duplication.

    Fix this by:
    - defining a new target hook low_init_process, called from
      linux_init_ptrace_procfs, which is called from both
      linux_nat_target::post_attach and
linux_nat_target::post_startup_inferior,
    - adding implementations for ppc_linux_nat_target and arm_linux_nat_target
      that detect the hardware watchpoint interface,
    - replacing the aarch64_linux_nat_target implementations of post_attach and
      post_startup_inferior with a low_init_process implementation.

    Tested on ppc64le-linux, arm-linux, aarch64-linux and x86_64-linux.

    Co-Authored-By: Tom de Vries <tdevries@suse.de>
    Approved-By: Luis Machado <luis.machado@arm.com>

    PR tdep/31834
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31834
    PR tdep/31705
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31705

    (cherry picked from commit 50de502a4f843310e231b3174804e95a9e7de4fc)

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