From 5a224b981ee32d7cf59aaa9e2c101af65a275edc Mon Sep 17 00:00:00 2001
From: Julien Lepiller <julien@lepiller.eu>
Date: Mon, 20 Feb 2023 19:14:12 +0100
Subject: [PATCH] Dynamically allocate the alternate signal stack.

This patch is a backport of https://github.com/ocaml/ocaml/pull/10266.
---
 asmrun/signals_asm.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/asmrun/signals_asm.c b/asmrun/signals_asm.c
index 3895d75..7e2abe8 100644
--- a/asmrun/signals_asm.c
+++ b/asmrun/signals_asm.c
@@ -182,7 +182,6 @@ DECLARE_SIGNAL_HANDLER(trap_handler)
 #ifdef HAS_STACK_OVERFLOW_DETECTION
 
 static char * system_stack_top;
-static char sig_alt_stack[SIGSTKSZ];
 
 #if defined(SYS_linux)
 /* PR#4746: recent Linux kernels with support for stack randomization
@@ -274,15 +273,19 @@ void caml_init_signals(void)
 #ifdef HAS_STACK_OVERFLOW_DETECTION
   {
     stack_t stk;
-    struct sigaction act;
-    stk.ss_sp = sig_alt_stack;
+    stk.ss_sp = malloc(SIGSTKSZ);
     stk.ss_size = SIGSTKSZ;
     stk.ss_flags = 0;
-    SET_SIGACT(act, segv_handler);
-    act.sa_flags |= SA_ONSTACK | SA_NODEFER;
-    sigemptyset(&act.sa_mask);
-    system_stack_top = (char *) &act;
-    if (sigaltstack(&stk, NULL) == 0) { sigaction(SIGSEGV, &act, NULL); }
+    if (stk.ss_sp != NULL) {
+      if (sigaltstack(&stk, NULL) != -1) {                                     
+        struct sigaction act;                                                  
+        SET_SIGACT(act, segv_handler);                                         
+        act.sa_flags |= SA_ONSTACK | SA_NODEFER;                               
+        sigemptyset(&act.sa_mask);                                             
+        system_stack_top = (char *) &act;                                      
+        sigaction(SIGSEGV, &act, NULL);                                        
+      }
+    }
   }
 #endif
 }
-- 
2.38.1

