From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 20 Jun 2011 21:59:13 +0000 (-0700)
Subject: c-stack: stop worrying about stack direction
X-Git-Tag: v0.1~2223
X-Git-Url: http://erislabs.org.uk/gitweb/?a=commitdiff_plain;h=3c4ad6125cf33faf3cc090b4232d35f3866b9799;p=gnulib.git

c-stack: stop worrying about stack direction

* lib/c-stack.c (find_stack_direction): Remove.
(segv_handler): Don't worry about stack direction growth, as it's
too much of a pain to configure this correctly, given how compilers
are optimizing-away our stack-growth detection code.  Instead, assume
that any access to just before or just after the stack is OK.
* m4/c-stack.m4 (AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC):
Don't require AC_FUNC_ALLOCA; no longer needed.
---

diff --git a/ChangeLog b/ChangeLog
index 1758d670f..d59548993 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2011-06-20  Paul Eggert  <eggert@cs.ucla.edu>
+
+	c-stack: stop worrying about stack direction
+	* lib/c-stack.c (find_stack_direction): Remove.
+	(segv_handler): Don't worry about stack direction growth, as it's
+	too much of a pain to configure this correctly, given how compilers
+	are optimizing-away our stack-growth detection code.  Instead, assume
+	that any access to just before or just after the stack is OK.
+	* m4/c-stack.m4 (AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC):
+	Don't require AC_FUNC_ALLOCA; no longer needed.
+
 2011-06-20  Eric Blake  <eblake@redhat.com>
 
 	test-stat: don't allocate PATH_MAX bytes
diff --git a/lib/c-stack.c b/lib/c-stack.c
index 7f0f48845..e48b97c3b 100644
--- a/lib/c-stack.c
+++ b/lib/c-stack.c
@@ -223,22 +223,6 @@ c_stack_action (void (*action) (int))
 
 #elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK && HAVE_STACK_OVERFLOW_HANDLING
 
-/* Direction of the C runtime stack.  This function is
-   async-signal-safe.  */
-
-# if STACK_DIRECTION
-#  define find_stack_direction(ptr) STACK_DIRECTION
-# else
-#  if ! SIGINFO_WORKS || HAVE_XSI_STACK_OVERFLOW_HEURISTIC
-static int
-find_stack_direction (char const *addr)
-{
-  char dummy;
-  return ! addr ? find_stack_direction (&dummy) : addr < &dummy ? 1 : -1;
-}
-#  endif
-# endif
-
 # if SIGINFO_WORKS
 
 /* Handle a segmentation violation and exit.  This function is
@@ -266,17 +250,14 @@ segv_handler (int signo, siginfo_t *info,
   if (0 < info->si_code)
     {
       /* If the faulting address is within the stack, or within one
-         page of the stack end, assume that it is a stack
-         overflow.  */
+         page of the stack, assume that it is a stack overflow.  */
       ucontext_t const *user_context = context;
       char const *stack_base = user_context->uc_stack.ss_sp;
       size_t stack_size = user_context->uc_stack.ss_size;
       char const *faulting_address = info->si_addr;
-      size_t s = faulting_address - stack_base;
       size_t page_size = sysconf (_SC_PAGESIZE);
-      if (find_stack_direction (NULL) < 0)
-        s += page_size;
-      if (s < stack_size + page_size)
+      size_t s = faulting_address - stack_base + page_size;
+      if (s < stack_size + 2 * page_size)
         signo = 0;
 
 #   if DEBUG
diff --git a/m4/c-stack.m4 b/m4/c-stack.m4
index d613fa8bd..8d34048e4 100644
--- a/m4/c-stack.m4
+++ b/m4/c-stack.m4
@@ -7,11 +7,10 @@
 
 # Written by Paul Eggert.
 
-# serial 12
+# serial 13
 
 AC_DEFUN([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC],
-  [# for STACK_DIRECTION
-   AC_REQUIRE([AC_FUNC_ALLOCA])
+  [
    AC_REQUIRE([AC_CANONICAL_HOST])
    AC_CHECK_FUNCS_ONCE([setrlimit])
    AC_CHECK_HEADERS_ONCE([ucontext.h])