[Bug gdb/27435] Attach on solaris segfaults GDB

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

https://sourceware.org/bugzilla/show_bug.cgi?id=27435

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Simon Marchi <simark@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=de146e1946ee45f2552c6b56714793a2eba9b823

commit de146e1946ee45f2552c6b56714793a2eba9b823
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Mon Feb 22 11:41:32 2021 -0500

    gdb: push target earlier in procfs_target::attach (PR 27435)

    Since this is a GDB 9 -> 10 regression, I would like to push it to
    gdb-10-branch.

    This is a follow-up to:

      https://sourceware.org/pipermail/gdb-patches/2021-February/176202.html

    This patch fixes a segfault seen when attaching to a process on Solaris.
    The steps leading to the segfault are:

     - procfs_target::attach calls do_attach, at this point the inferior's
       process slot in the target stack is empty.
     - do_attach adds a thread with `add_thread (&the_procfs_target, ptid)`
     - in add_thread_silent, the passed target (&the_procfs_target) is
       passed to find_inferior_ptid
     - find_inferior_ptid returns nullptr, as there is no inferior with this
       ptid that has &the_procfs_target as its process target
     - the nullptr `inf` is passed to find_thread_ptid, which dereferences
       it, causing a segfault
     - back in procfs_target::attach, after do_attach, we push the
       the_procfs_target on the inferior's target stack, although we never
       reach this because the segfault happens before.

    To fix this, I think we need to do the same as is done in
    inf_ptrace_target::attach: push the target early and unpush it in case
    the attach fails (and keep it if the attach succeeds).

    Implement it by moving target_unpush_up to target.h, so it can be
    re-used here.  Make procfs_target::attach use it.  Note that just like
    is mentioned in inf_ptrace_target::attach, we should push the target
    before calling target_pid_to_str, so that calling target_pid_to_str ends
    up in procfs_target::pid_to_str.

    Tested by trying to attach on a process on gcc211 on the gcc compile
    farm.

    gdb/ChangeLog:

            PR gdb/27435
            * inf-ptrace.c (struct target_unpusher): Move to target.h.
            (target_unpush_up): Likewise.
            * procfs.c (procfs_target::attach): Push target early.  Use
            target_unpush_up to unpush target in case of error.
            * target.h (struct target_unpusher): Move here.
            (target_unpush_up): Likewise.

    Change-Id: I88aff8b20204e1ca1d792e27ac6bc34fc1aa0d52

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