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authorSimon Marchi <simon.marchi@polymtl.ca>2021-02-22 11:41:32 -0500
committerSimon Marchi <simon.marchi@polymtl.ca>2021-02-22 11:41:32 -0500
commitde146e1946ee45f2552c6b56714793a2eba9b823 (patch)
tree1811fc36f8bbb5e772aefdbab83816e3eb755c28 /gdb/procfs.c
parente9d18e0649ae83fcfafd325a2366973efde43b38 (diff)
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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
Diffstat (limited to 'gdb/procfs.c')
-rw-r--r--gdb/procfs.c14
1 files changed, 12 insertions, 2 deletions
diff --git a/gdb/procfs.c b/gdb/procfs.c
index e73faa8..cab29c3 100644
--- a/gdb/procfs.c
+++ b/gdb/procfs.c
@@ -1767,6 +1767,14 @@ procfs_target::attach (const char *args, int from_tty)
if (pid == getpid ())
error (_("Attaching GDB to itself is not a good idea..."));
+ /* Push the target if needed, ensure it gets un-pushed it if attach fails. */
+ target_unpush_up unpusher;
+ if (!target_is_pushed (this))
+ {
+ push_target (this);
+ unpusher.reset (this);
+ }
+
if (from_tty)
{
const char *exec_file = get_exec_file (0);
@@ -1780,9 +1788,11 @@ procfs_target::attach (const char *args, int from_tty)
fflush (stdout);
}
+
do_attach (ptid_t (pid));
- if (!target_is_pushed (this))
- push_target (this);
+
+ /* Everything went fine, keep the target pushed. */
+ unpusher.release ();
}
void