[gdb] Fix tsan warning: signal handler spoils errno

When building gdb with -fsanitize=thread and running test-case
gdb.base/bg-exec-sigint-bp-cond.exp, I run into:
...
==================^M
WARNING: ThreadSanitizer: signal handler spoils errno (pid=25422)^M
    #0 handler_wrapper gdb/posix-hdep.c:66^M
    #1 decltype ({parm#2}({parm#3}...)) gdb::handle_eintr<>() \
         gdbsupport/eintr.h:67^M
    #2 gdb::waitpid(int, int*, int) gdbsupport/eintr.h:78^M
    #3 run_under_shell gdb/cli/cli-cmds.c:926^M
...

Likewise in:
- tui_sigwinch_handler with test-case gdb.python/tui-window.exp, and
- handle_sighup with test-case gdb.base/quit-live.exp.

Fix this by saving the original errno, and restoring it before returning [1].

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

[1] https://www.gnu.org/software/libc/manual/html_node/POSIX-Safety-Concepts.html

3 files changed, 3 insertions, 0 deletions

diff --git a/gdb/event-top.c b/gdb/event-top.c
index 45ad7b9..102304c 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -1480,6 +1480,7 @@ async_do_nothing (gdb_client_data arg)
 static void
 handle_sighup (int sig)
 {
+  scoped_restore restore_errno = make_scoped_restore (&errno);
   mark_async_signal_handler (sighup_token);
   signal (sig, handle_sighup);
 }
diff --git a/gdb/posix-hdep.c b/gdb/posix-hdep.c
index a0d5c58..d7d17e6 100644
--- a/gdb/posix-hdep.c
+++ b/gdb/posix-hdep.c
@@ -64,6 +64,7 @@ static c_c_handler_ftype *current_handler;
 static void
 handler_wrapper (int num)
 {
+  scoped_restore restore_errno = make_scoped_restore (&errno);
   signal (num, handler_wrapper);
   if (current_handler != SIG_IGN)
     current_handler (num);
diff --git a/gdb/tui/tui-win.c b/gdb/tui/tui-win.c
index e9a8e46..414d469 100644
--- a/gdb/tui/tui-win.c
+++ b/gdb/tui/tui-win.c
@@ -527,6 +527,7 @@ static struct async_signal_handler *tui_sigwinch_token;
 static void
 tui_sigwinch_handler (int signal)
 {
+  scoped_restore restore_errno = make_scoped_restore (&errno);
   mark_async_signal_handler (tui_sigwinch_token);
   tui_set_win_resized_to (true);
 }