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Re: c-stack: use libsigsegv when possible
From: |
Eric Blake |
Subject: |
Re: c-stack: use libsigsegv when possible |
Date: |
Thu, 17 Jul 2008 07:33:24 -0600 |
User-agent: |
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.14) Gecko/20080421 Thunderbird/2.0.0.14 Mnenhy/0.7.5.666 |
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According to Eric Blake on 7/16/2008 9:11 PM:
| According to Bruno Haible on 7/16/2008 7:29 PM:
| | If you want to save linking with libsigsegv, just do the test
| | '#if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC' at configure
| | time rather than at compile-time, create two new variables LIBCSTACK and
| | LTLIBCSTACK, AC_SUBST them, and document in modudes/c-stack that the
| | appropriate of these two variables needs to be used while linking.
|
| OK, I'll rework the patch along those lines.
Committed as follows (and this is what exposed the libsigsegv on OpenBSD 4.0).
- --
Don't work too hard, make some time for fun as well!
Eric Blake address@hidden
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>From f6a65c23356574113f91060f82cef2119af4949a Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Thu, 17 Jul 2008 06:23:47 -0600
Subject: [PATCH] Make c-stack use libsigsegv, when available.
* modules/c-stack (Depends-on): Add libsigsegv.
* modules/c-stack-tests (Makefile.am): Link with libsigsegv, if
needed.
* lib/c-stack.c (SIGSTKSZ): Define fallback.
(segv_handler, overflow_handler, c_stack_action)
[HAVE_LIBSIGSEGV && !HAVE_XSI_STACK_OVERFLOW_HEURISTIC]: Add new
implementation when libsigsegv is available, but only when using
the library is necessary.
* m4/c-stack.m4 (AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC): Add
comment, explaining why XSI check fails on Linux.
(gl_PREREQ_C_STACK): Supply LIBCSTACK, LTLIBCSTACK.
* tests/test-c-stack2.sh: Tweak skip message.
* NEWS: Document new link-time requirements.
Signed-off-by: Eric Blake <address@hidden>
---
ChangeLog | 17 ++++++
NEWS | 4 +
lib/c-stack.c | 150 +++++++++++++++++++++++++++++++++++++++++-------
m4/c-stack.m4 | 16 +++++-
modules/c-stack | 4 +
modules/c-stack-tests | 2 +-
tests/test-c-stack2.sh | 2 +-
7 files changed, 169 insertions(+), 26 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 0772f2d..01f0084 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,20 @@
+2008-07-17 Eric Blake <address@hidden>
+
+ Make c-stack use libsigsegv, when available.
+ * modules/c-stack (Depends-on): Add libsigsegv.
+ * modules/c-stack-tests (Makefile.am): Link with libsigsegv, if
+ needed.
+ * lib/c-stack.c (SIGSTKSZ): Define fallback.
+ (segv_handler, overflow_handler, c_stack_action)
+ [HAVE_LIBSIGSEGV && !HAVE_XSI_STACK_OVERFLOW_HEURISTIC]: Add new
+ implementation when libsigsegv is available, but only when using
+ the library is necessary.
+ * m4/c-stack.m4 (AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC): Add
+ comment, explaining why XSI check fails on Linux.
+ (gl_PREREQ_C_STACK): Supply LIBCSTACK, LTLIBCSTACK.
+ * tests/test-c-stack2.sh: Tweak skip message.
+ * NEWS: Document new link-time requirements.
+
2008-07-16 Eric Blake <address@hidden>
c-stack: Expose false positives when not using libsigsegv.
diff --git a/NEWS b/NEWS
index 74ca234..da75d7f 100644
--- a/NEWS
+++ b/NEWS
@@ -6,6 +6,10 @@ User visible incompatible changes
Date Modules Changes
+2008-07-17 c-stack The module now requires the addition of
+ $(LIBCSTACK) or $(LTLIBCSTACK) in Makefile.am,
+ since it may depend on linking with libsigsegv.
+
2008-07-07 isnanf-nolibm The include file is changed from "isnanf.h"
to "isnanf-nolibm.h".
isnand-nolibm The include file is changed from "isnand.h"
diff --git a/lib/c-stack.c b/lib/c-stack.c
index 96bd2bf..c81fbfa 100644
--- a/lib/c-stack.c
+++ b/lib/c-stack.c
@@ -53,6 +53,9 @@
#if ! HAVE_STACK_T && ! defined stack_t
typedef struct sigaltstack stack_t;
#endif
+#ifndef SIGSTKSZ
+# define SIGSTKSZ 16384
+#endif
#include <stdlib.h>
#include <string.h>
@@ -68,6 +71,10 @@ typedef struct sigaltstack stack_t;
# define STDERR_FILENO 2
#endif
+#if HAVE_LIBSIGSEGV
+# include <sigsegv.h>
+#endif
+
#include "c-stack.h"
#include "exitfail.h"
@@ -110,7 +117,115 @@ die (int signo)
abort ();
}
-#if HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
+#if (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK) || HAVE_LIBSIGSEGV
+
+/* Storage for the alternate signal stack. */
+static union
+{
+ char buffer[SIGSTKSZ];
+
+ /* These other members are for proper alignment. There's no
+ standard way to guarantee stack alignment, but this seems enough
+ in practice. */
+ long double ld;
+ long l;
+ void *p;
+} alternate_signal_stack;
+
+static void
+null_action (int signo __attribute__ ((unused)))
+{
+}
+
+#endif /* SIGALTSTACK || LIBSIGSEGV */
+
+/* Only use libsigsegv if we need it; platforms like Solaris can
+ detect stack overflow without the overhead of an external
+ library. */
+#if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
+
+/* Nonzero if general segv handler could not be installed. */
+static volatile int segv_handler_missing;
+
+/* Handle a segmentation violation and exit if it cannot be stack
+ overflow. This function is async-signal-safe. */
+
+static int segv_handler (void *address __attribute__ ((unused)),
+ int serious)
+{
+# if DEBUG
+ {
+ char buf[1024];
+ sprintf (buf, "segv_handler serious=%d\n", serious);
+ write (STDERR_FILENO, buf, strlen (buf));
+ }
+# endif
+
+ /* If this fault is not serious, return 0 to let the stack overflow
+ handler take a shot at it. */
+ if (!serious)
+ return 0;
+ die (SIGSEGV);
+}
+
+/* Handle a segmentation violation that is likely to be a stack
+ overflow and exit. This function is async-signal-safe. */
+
+static void overflow_handler (int, stackoverflow_context_t)
+ __attribute__ ((noreturn));
+static void
+overflow_handler (int emergency,
+ stackoverflow_context_t context __attribute__ ((unused)))
+{
+# if DEBUG
+ {
+ char buf[1024];
+ sprintf (buf, "overflow_handler emergency=%d segv_handler_missing=%d\n",
+ emergency, segv_handler_missing);
+ write (STDERR_FILENO, buf, strlen (buf));
+ }
+# endif
+
+ die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
+}
+
+/* Set up ACTION so that it is invoked on C stack overflow. Return -1
+ (setting errno) if this cannot be done.
+
+ When ACTION is called, it is passed an argument equal to SIGSEGV
+ for a segmentation violation that does not appear related to stack
+ overflow, and is passed zero otherwise. On many platforms it is
+ hard to tell; when in doubt, zero is passed.
+
+ A null ACTION acts like an action that does nothing.
+
+ ACTION must be async-signal-safe. ACTION together with its callees
+ must not require more than SIGSTKSZ bytes of stack space. Also,
+ ACTION should not call longjmp, because this implementation does
+ not guarantee that it is safe to return to the original stack. */
+
+int
+c_stack_action (void (*action) (int))
+{
+ segv_action = action ? action : null_action;
+ program_error_message = _("program error");
+ stack_overflow_message = _("stack overflow");
+
+ /* Always install the overflow handler. */
+ if (stackoverflow_install_handler (overflow_handler,
+ alternate_signal_stack.buffer,
+ sizeof alternate_signal_stack.buffer))
+ {
+ errno = ENOTSUP;
+ return -1;
+ }
+ /* Try installing a general handler; if it fails, then treat all
+ segv as stack overflow. */
+ segv_handler_missing = sigsegv_install_handler (segv_handler);
+ return 0;
+}
+
+#elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
/* Direction of the C runtime stack. This function is
async-signal-safe. */
@@ -126,19 +241,6 @@ find_stack_direction (char const *addr)
}
# endif
-/* Storage for the alternate signal stack. */
-static union
-{
- char buffer[SIGSTKSZ];
-
- /* These other members are for proper alignment. There's no
- standard way to guarantee stack alignment, but this seems enough
- in practice. */
- long double ld;
- long l;
- void *p;
-} alternate_signal_stack;
-
# if SIGACTION_WORKS
/* Handle a segmentation violation and exit. This function is
@@ -155,7 +257,14 @@ segv_handler (int signo, siginfo_t *info,
# if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
/* We can't easily determine whether it is a stack overflow; so
assume that the rest of our program is perfect (!) and that
- this segmentation violation is a stack overflow. */
+ this segmentation violation is a stack overflow.
+
+ Note that although both Linux and Solaris provide
+ sigaltstack, SA_ONSTACK, and SA_SIGINFO, currently only
+ Solaris satisfies the XSI heueristic. This is because
+ Solaris populates uc_stack with the details of the
+ interrupted stack, while Linux populates it with the details
+ of the current stack. */
signo = 0;
# else
/* If the faulting address is within the stack, or within one
@@ -189,11 +298,6 @@ segv_handler (int signo, siginfo_t *info,
}
# endif
-static void
-null_action (int signo __attribute__ ((unused)))
-{
-}
-
/* Set up ACTION so that it is invoked on C stack overflow. Return -1
(setting errno) if this cannot be done.
@@ -205,7 +309,9 @@ null_action (int signo __attribute__ ((unused)))
A null ACTION acts like an action that does nothing.
ACTION must be async-signal-safe. ACTION together with its callees
- must not require more than SIGSTKSZ bytes of stack space. */
+ must not require more than SIGSTKSZ bytes of stack space. Also,
+ ACTION should not call longjmp, because this implementation does
+ not guarantee that it is safe to return to the original stack. */
int
c_stack_action (void (*action) (int))
@@ -240,7 +346,7 @@ c_stack_action (void (*action) (int))
return sigaction (SIGSEGV, &act, NULL);
}
-#else /* ! (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK) */
+#else /* ! ((HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK) || HAVE_LIBSIGSEGV) */
int
c_stack_action (void (*action) (int) __attribute__ ((unused)))
diff --git a/m4/c-stack.m4 b/m4/c-stack.m4
index f142171..b1f93ed 100644
--- a/m4/c-stack.m4
+++ b/m4/c-stack.m4
@@ -7,7 +7,7 @@
# Written by Paul Eggert.
-# serial 2
+# serial 3
AC_DEFUN([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC],
[# for STACK_DIRECTION
@@ -55,6 +55,9 @@ AC_DEFUN([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC],
{
if (0 < info->si_code)
{
+ /* For XSI heuristics to work, we need uc_stack to describe
+ the interrupted stack (as on Solaris), and not the
+ currently executing stack (as on Linux). */
ucontext_t const *user_context = context;
char const *stack_min = user_context->uc_stack.ss_sp;
size_t stack_size = user_context->uc_stack.ss_size;
@@ -133,6 +136,7 @@ AC_DEFUN([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC],
AC_DEFUN([gl_PREREQ_C_STACK],
[AC_REQUIRE([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC])
+ AC_REQUIRE([gl_LIBSIGSEGV])
# for STACK_DIRECTION
AC_REQUIRE([AC_FUNC_ALLOCA])
@@ -144,7 +148,15 @@ AC_DEFUN([gl_PREREQ_C_STACK],
AC_CHECK_MEMBERS([struct sigaction.sa_sigaction], , , [#include <signal.h>])
- AC_CHECK_TYPES([stack_t], , , [#include <signal.h>])])
+ AC_CHECK_TYPES([stack_t], , , [#include <signal.h>])
+
+ dnl c-stack does not need -lsigsegv if the system has XSI heuristics.
+ if test "$gl_cv_lib_sigsegv" = yes \
+ && test $"ac_cv_sys_xsi_stack_overflow_heuristic" != yes ; then
+ AC_SUBST([LIBCSTACK], [$LIBSIGSEGV])
+ AC_SUBST([LTLIBCSTACK], [$LTLIBSIGSEGV])
+ fi
+])
AC_DEFUN([gl_C_STACK],
[
diff --git a/modules/c-stack b/modules/c-stack
index d3e7e09..a01b8c7 100644
--- a/modules/c-stack
+++ b/modules/c-stack
@@ -12,6 +12,7 @@ exitfail
unistd
raise
sigaction
+libsigsegv
configure.ac:
gl_C_STACK
@@ -22,6 +23,9 @@ lib_SOURCES += c-stack.h c-stack.c
Include:
"c-stack.h"
+Link:
+$(LTCSTACK) when linking with libtool, $(LIBCSTACK) otherwise
+
License:
GPL
diff --git a/modules/c-stack-tests b/modules/c-stack-tests
index 5d3bc58..4cf15f2 100644
--- a/modules/c-stack-tests
+++ b/modules/c-stack-tests
@@ -12,5 +12,5 @@ Makefile.am:
TESTS += test-c-stack.sh test-c-stack2.sh
TESTS_ENVIRONMENT += EXEEXT='@EXEEXT@'
check_PROGRAMS += test-c-stack
-test_c_stack_LDADD = $(LDADD) @LIBINTL@
+test_c_stack_LDADD = $(LDADD) $(LIBCSTACK) @LIBINTL@
MOSTLYCLEANFILES += t-c-stack.tmp t-c-stack2.tmp
diff --git a/tests/test-c-stack2.sh b/tests/test-c-stack2.sh
index e55ff17..039a819 100755
--- a/tests/test-c-stack2.sh
+++ b/tests/test-c-stack2.sh
@@ -11,7 +11,7 @@ tmpfiles="t-c-stack2.tmp"
case $? in
77) if grep 'stack overflow' t-c-stack2.tmp >/dev/null ; then
- echo 'cannot distinguish stack overflow from crash' >&2
+ echo 'cannot tell stack overflow from crash; consider installing
libsigsegv' >&2
else
cat t-c-stack2.tmp >&2
fi
--
1.5.6