-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
I'm still working on improving the async-safety in my proposed sigaction
module, and found that it would somewhat easier if I could learn accurate
signal information even when a signal is blocked. Is this okay to apply?
- --
Don't work too hard, make some time for fun as well!
Eric Blake [EMAIL PROTECTED]
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (Cygwin)
Comment: Public key at home.comcast.net/~ericblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org
iEYEARECAAYFAkhbsG4ACgkQ84KuGfSFAYDO/wCgtdjg1JNC5hTAxN8AbzqPnBuC
tTEAoNMPu0I47SJhWiHZnhp9vrq2TCWq
=uMFd
-----END PGP SIGNATURE-----
>From 149ab1ac923f1d86e6bf1177cb2a30a990f34793 Mon Sep 17 00:00:00 2001
From: Eric Blake <[EMAIL PROTECTED]>
Date: Fri, 20 Jun 2008 07:27:08 -0600
Subject: [PATCH] Improve robustness of sigprocmask by overriding signal.
* lib/signal.in.h (includes): Hoist <sys/types.h> outside of
extern "C" block.
(rpl_signal): Override signal when sigprocmask is in use.
* lib/sigprocmask.c (blocked_handler): Reinstall block handler.
(SIGKILL, SIGSTOP): Provide fallbacks.
(rpl_signal): Implement.
Signed-off-by: Eric Blake <[EMAIL PROTECTED]>
---
ChangeLog | 10 ++++++++
lib/signal.in.h | 14 ++++++++---
lib/sigprocmask.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 78 insertions(+), 7 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index bdb444a..8b71ccc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2008-06-20 Eric Blake <[EMAIL PROTECTED]>
+
+ Improve robustness of sigprocmask by overriding signal.
+ * lib/signal.in.h (includes): Hoist <sys/types.h> outside of
+ extern "C" block.
+ (rpl_signal): Override signal when sigprocmask is in use.
+ * lib/sigprocmask.c (blocked_handler): Reinstall block handler.
+ (SIGKILL, SIGSTOP): Provide fallbacks.
+ (rpl_signal): Implement.
+
2008-06-19 Bruno Haible <[EMAIL PROTECTED]>
Fix CVS-ism.
diff --git a/lib/signal.in.h b/lib/signal.in.h
index 9f82ba7..eb16afb 100644
--- a/lib/signal.in.h
+++ b/lib/signal.in.h
@@ -1,6 +1,6 @@
/* A GNU-like <signal.h>.
- Copyright (C) 2006-2007 Free Software Foundation, Inc.
+ Copyright (C) 2006-2008 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
@@ -33,6 +33,10 @@
/* The definition of GL_LINK_WARNING is copied here. */
+/* Mingw defines sigset_t not in <signal.h>, but in <sys/types.h>. */
+#if [EMAIL PROTECTED]@
+# include <sys/types.h>
+#endif
#ifdef __cplusplus
extern "C" {
@@ -41,9 +45,6 @@ extern "C" {
#if [EMAIL PROTECTED]@
-/* Mingw defines sigset_t not in <signal.h>, but in <sys/types.h>. */
-# include <sys/types.h>
-
/* Maximum signal number + 1. */
# ifndef NSIG
# define NSIG 32
@@ -85,6 +86,11 @@ extern int sigpending (sigset_t *set);
# define SIG_UNBLOCK 2 /* blocked_set = blocked_set & ~*set; */
extern int sigprocmask (int operation, const sigset_t *set, sigset_t *old_set);
+# define signal rpl_signal
+/* Install the handler FUNC for signal SIG, and return the previous
+ handler. */
+extern void (*signal (int sig, void (*func) (int))) (int);
+
#endif
diff --git a/lib/sigprocmask.c b/lib/sigprocmask.c
index 456545a..a895631 100644
--- a/lib/sigprocmask.c
+++ b/lib/sigprocmask.c
@@ -24,9 +24,24 @@
#include <stdint.h>
#include <stdlib.h>
-/* We assume that a platform without POSIX signal blocking functions also
- does not have the POSIX sigaction() function, only the signal() function.
- This is true for Woe32 platforms. */
+/* We assume that a platform without POSIX signal blocking functions
+ also does not have the POSIX sigaction() function, only the
+ signal() function. We also assume signal() has SysV semantics,
+ where any handler is uninstalled prior to being invoked. This is
+ true for Woe32 platforms. */
+
+/* We use raw signal(), but also provide a wrapper rpl_signal() so
+ that applications can query or change a blocked signal. */
+#undef signal
+
+/* Provide invalid signal numbers as fallbacks if the uncatchable
+ signals are not defined. */
+#ifndef SIGKILL
+# define SIGKILL (-1)
+#endif
+#ifndef SIGSTOP
+# define SIGSTOP (-1)
+#endif
/* A signal handler. */
typedef void (*handler_t) (int signal);
@@ -94,6 +109,12 @@ static volatile sig_atomic_t pending_array[NSIG] /* = { 0 }
*/;
static void
blocked_handler (int sig)
{
+ /* Reinstall the handler, in case the signal occurs multiple times
+ while blocked. There is an inherent race where an asynchronous
+ signal in between when the kernel uninstalled the handler and
+ when we reinstall it will trigger the default handler; oh
+ well. */
+ signal (sig, blocked_handler);
if (sig >= 0 && sig < NSIG)
pending_array[sig] = 1;
}
@@ -184,3 +205,37 @@ sigprocmask (int operation, const sigset_t *set, sigset_t
*old_set)
}
return 0;
}
+
+/* Install the handler FUNC for signal SIG, and return the previous
+ handler. */
+handler_t
+rpl_signal (int sig, handler_t handler)
+{
+ /* We must provide a wrapper, so that a user can query what handler
+ they installed even if that signal is currently blocked. */
+ if (sig >= 0 && sig < NSIG && sig != SIGKILL && sig != SIGSTOP
+ && handler != SIG_ERR)
+ {
+ if (blocked_set & (1U << sig))
+ {
+ /* POSIX states that sigprocmask and signal are both
+ async-signal-safe. This is not true of our
+ implementation - there is a slight data race where an
+ asynchronous interrupt on signal A can occur after we
+ install blocked_handler but before we have updated
+ old_handlers for signal B, such that handler A can see
+ stale information if it calls signal(B). Oh well -
+ signal handlers really shouldn't try to manipulate the
+ installed handlers of unrelated signals. */
+ handler_t result = old_handlers[sig];
+ old_handlers[sig] = handler;
+ return result;
+ }
+ return signal (sig, handler);
+ }
+ else
+ {
+ errno = EINVAL;
+ return SIG_ERR;
+ }
+}
--
1.5.5.1
