Re: Two issues with stack overflow protection

[Paul Eggert <eggert@cs.ucla.edu>]

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Eli Zaretskii wrote:
> The implementation of stack_overflow on sysdep.c was recently changed
> so as not to use sys/resource.h and getrlimit, but configure.ac still
> insists on these two features in order to include the recovery code,
> which I think should be fixed.

Thanks, fixed with the attached patch.

> More importantly, the recovery simply longjmps to command_loop,
> whereas similar features like Fthrow and Fsignal do much more in
> unwind_to_catch.  Shouldn't stack overflow recovery do that as well?
> Otherwise, the specpdl stack, byte_stack_list, lisp_eval_depth
> etc. all stay at their values they had at stack overflow time, no?

No, they are cleared back to top-level values, because when command_loop's call 
to sigsetjmp returns nonzero, it then calls init_eval and this resets them.

There is a problem that the speclpdl stack's unwind-protect and 
dynamic-let-bindings are unceremoniously discarded on stack overflow.  I suppose 
that should get fixed, though it may be a bit tricky to avoid looping.

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From 2377572a880400182cd370c5ca104c7151e0f20c Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 28 Jul 2015 21:41:59 -0700
Subject: [PATCH] Remove unnecessary stack overflow dependency

* configure.ac (HAVE_STACK_OVERFLOW_HANDLING):
Don't worry about $ac_cv_header_sys_resource_h and
$ac_cv_func_getrlimit, as they're no longer needed for this.
Problem reported by Eli Zaretskii in:
http://lists.gnu.org/archive/html/emacs-devel/2015-07/msg00443.html
---
 configure.ac | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/configure.ac b/configure.ac
index 19b8b9d..45008d8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4557,9 +4557,7 @@ if test $emacs_cv_func_sigsetjmp = yes; then
 fi
 
 # We need all of these features to handle C stack overflows.
-if test "$ac_cv_header_sys_resource_h" = "yes" &&
-   test "$ac_cv_func_getrlimit" = "yes" &&
-   test "$emacs_cv_func_sigsetjmp" = "yes" &&
+if test "$emacs_cv_func_sigsetjmp" = "yes" &&
    test "$emacs_cv_alternate_stack" = yes; then
   AC_DEFINE([HAVE_STACK_OVERFLOW_HANDLING], 1,
     [Define to 1 if C stack overflow can be handled in some cases.])
-- 
2.1.0