From f97e07ea807cc6d38774a3888a15091b20645ac6 Mon Sep 17 00:00:00 2001

From: Paul Eggert <eggert@cs.ucla.edu>

Date: Tue, 9 Mar 2021 11:22:59 -0800

Subject: [PATCH] Port alternate signal stack to upcoming glibc 2.34

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* 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.

---

 src/sysdep.c | 10 +++++++++-

 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/sysdep.c b/src/sysdep.c

index 941b4e2fa2..24d8832b2f 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.  */

-- 

2.29.2