Re: [PATCH 2/5] hurd: Microoptimize sigreturn

[Sergey Bugaev]

(Git managed to eat my email -- it both sent an empty one *and*
truncated my local file (what?); so retyping and resending this.)

On Tue, Apr 18, 2023 at 2:23 AM Samuel Thibault <samuel.thibault@gnu.org> wrote:
> That doesn't seem to be true, we get segfaults with this patch applied
> in these tests:
>
> ./htl/tst-kill6.test-result:FAIL: htl/tst-kill6
> ./htl/tst-pt-tls2.test-result:FAIL: htl/tst-pt-tls2
>
> #0  0x0105a7c2 in sigstate_is_global_rcv (ss=0x0) at hurdsig.c:183
> 183              && (ss->actions[0].sa_handler == SIG_IGN);
> (gdb) bt
> #0  0x0105a7c2 in sigstate_is_global_rcv (ss=0x0) at hurdsig.c:183
> #1  __GI__hurd_sigstate_lock (ss=0x0) at hurdsig.c:192
> #2  0x0108bb17 in __sigreturn (scp=0x2104bec) at 
> ../sysdeps/mach/hurd/i386/sigreturn.c:94
> #3  0x010602f6 in trampoline () from ./libc.so.0.3

Interesting; so while the sigstate for the thread must have been
initialized, it seems it has never been installed into the
tcb->_hurd_sigstate slot, because the thread has never called
_hurd_self_sigstate (). So we have to make the full call to
_hurd_self_sigstate () the first time, to find the sigstate and
install it into the slot.

Please try this:

Sergey

---- >8 ----


>From 94fc9499390b4de9fbe10c3014d473ac42878c6a Mon Sep 17 00:00:00 2001
From: Sergey Bugaev <bugaevc@gmail.com>
Date: Fri, 14 Apr 2023 16:32:45 +0300
Subject: [PATCH] hurd: Microoptimize sigreturn

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
 sysdeps/mach/hurd/i386/sigreturn.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/sysdeps/mach/hurd/i386/sigreturn.c 
b/sysdeps/mach/hurd/i386/sigreturn.c
index a0fc8891..1686734d 100644
--- a/sysdeps/mach/hurd/i386/sigreturn.c
+++ b/sysdeps/mach/hurd/i386/sigreturn.c
@@ -29,7 +29,12 @@ static void
 __sigreturn2 (int *usp, struct sigcontext *scp)
 {
   mach_port_t reply_port;
-  struct hurd_sigstate *ss = _hurd_self_sigstate ();
+  struct hurd_sigstate *ss;
+
+  /* We know the sigstate must be initialized by the call below, but the
+     compiler does not.  Help it out a little bit by eliding the check that
+     _hurd_self_sigstate makes otherwise.  */
+  ss = THREAD_GETMEM (THREAD_SELF, _hurd_sigstate);
   _hurd_sigstate_unlock (ss);
 
   /* Destroy the MiG reply port used by the signal handler, and restore the
@@ -44,7 +49,7 @@ __sigreturn2 (int *usp, struct sigcontext *scp)
      do.  */
   reply_port = THREAD_GETMEM (THREAD_SELF, reply_port);
   THREAD_SETMEM (THREAD_SELF, reply_port, MACH_PORT_DEAD);
-  if (MACH_PORT_VALID (reply_port))
+  if (__glibc_likely (MACH_PORT_VALID (reply_port)))
     (void) __mach_port_mod_refs (__mach_task_self (), reply_port,
                                  MACH_PORT_RIGHT_RECEIVE, -1);
   THREAD_SETMEM (THREAD_SELF, reply_port, scp->sc_reply_port);
@@ -69,6 +74,7 @@ __sigreturn2 (int *usp, struct sigcontext *scp)
   /* Firewall.  */
   A (hlt);
 #undef A
+  __builtin_unreachable ();
 }
 
 int
@@ -77,7 +83,7 @@ __sigreturn (struct sigcontext *scp)
   struct hurd_sigstate *ss;
   struct hurd_userlink *link = (void *) &scp[1];
 
-  if (scp == NULL || (scp->sc_mask & _SIG_CANT_MASK))
+  if (__glibc_unlikely (scp == NULL || (scp->sc_mask & _SIG_CANT_MASK)))
     {
       errno = EINVAL;
       return -1;
-- 
2.39.2