From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 9 Mar 2021 19:22:59 +0000 (-0800)
Subject: Port alternate signal stack to upcoming glibc 2.34
X-Git-Tag: emacs-28.0.90~3352
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=f97e07ea807cc6d38774a3888a15091b20645ac6;p=emacs.git

Port alternate signal stack to upcoming glibc 2.34

* src/sysdep.c (sigsegv_stack): Increase size to 64 KiB and align
it to max_align_t.  This copies from Gnulib’s c-stack.c, and works
around a portability bug in draft glibc 2.34, which no longer
defines SIGSTKSZ when _GNU_SOURCE is defined.
---

diff --git a/src/sysdep.c b/src/sysdep.c
index 941b4e2fa24..24d8832b2f3 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -1785,7 +1785,15 @@ handle_arith_signal (int sig)
 
 /* Alternate stack used by SIGSEGV handler below.  */
 
-static unsigned char sigsegv_stack[SIGSTKSZ];
+/* Storage for the alternate signal stack.
+   64 KiB is not too large for Emacs, and is large enough
+   for all known platforms.  Smaller sizes may run into trouble.
+   For example, libsigsegv 2.6 through 2.8 have a bug where some
+   architectures use more than the Linux default of an 8 KiB alternate
+   stack when deciding if a fault was caused by stack overflow.  */
+static max_align_t sigsegv_stack[(64 * 1024
+				  + sizeof (max_align_t) - 1)
+				 / sizeof (max_align_t)];
 
 
 /* Return true if SIGINFO indicates a stack overflow.  */