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.