A patch for darwin's Libc-825.25, which fixes a bug that backtrace(3) doesn't work if it is called from signal handler when it uses alternate signal stack. http://www.opensource.apple.com/source/Libc/Libc-825.25/gen/thread_stack_pcs.c

thread_stack_pcs.patch

--- gen/thread_stack_pcs.c.orig  2013-02-04 15:51:02.000000000 +0900
+++ gen/thread_stack_pcs.c	2013-02-05 14:45:47.000000000 +0900
@@ -37,6 +37,7 @@
 #endif
 
 #define	INSTACK(a)	((a) >= stackbot && (a) <= stacktop)
+#define	INALTSTACK(a)	((a) >= altstackbot && (a) <= altstacktop)
 #if defined(__ppc__) || defined(__ppc64__) || defined(__x86_64__)
 #define	ISALIGNED(a)	((((uintptr_t)(a)) & 0xf) == 0)
 #elif defined(__arm__) 
@@ -53,11 +54,19 @@ _thread_stack_pcs(vm_address_t *buffer, 
     pthread_t self = pthread_self();
     void *stacktop = pthread_get_stackaddr_np(self);
     void *stackbot = stacktop - pthread_get_stacksize_np(self);
+    stack_t ss;
+    int res = sigaltstack(NULL, &ss);
+    void *altstackbot, *altstacktop;
 
     *nb = 0;
+    if (res) return;
+
+    altstackbot = ss.ss_sp;
+    altstacktop = (void *)((intptr_t)altstackbot + (intptr_t)ss.ss_size);
 
     /* make sure return address is never out of bounds */
     stacktop -= (FP_LINK_OFFSET + 1) * sizeof(void *);
+    altstacktop -= (FP_LINK_OFFSET + 1) * sizeof(void *);
 
     /*
      * The original implementation called the first_frame_address() function,
@@ -73,18 +82,18 @@ _thread_stack_pcs(vm_address_t *buffer, 
     /* __builtin_frame_address IS BROKEN IN BEAKER: RADAR #2340421 */
     __asm__ volatile("mr %0, r1" : "=r" (frame));
 #endif
-    if(!INSTACK(frame) || !ISALIGNED(frame))
+    if(!INSTACK(frame) || !INALTSTACK(frame) || !ISALIGNED(frame))
 	return;
 #if defined(__ppc__) || defined(__ppc64__)
     /* back up the stack pointer up over the current stack frame */
     next = *(void **)frame;
-    if(!INSTACK(next) || !ISALIGNED(next) || next <= frame)
+    if(!INSTACK(next) || !INALTSTACK(next) || !ISALIGNED(next) || next <= frame)
 	return;
     frame = next;
 #endif
     while (skip--) {
 	next = *(void **)frame;
-	if(!INSTACK(next) || !ISALIGNED(next) || next <= frame)
+	if(!INSTACK(next) || !INALTSTACK(next) || !ISALIGNED(next) || next <= frame)
 	    return;
 	frame = next;
     }
@@ -92,7 +101,7 @@ _thread_stack_pcs(vm_address_t *buffer, 
         buffer[*nb] = *(vm_address_t *)(((void **)frame) + FP_LINK_OFFSET);
         (*nb)++;
 	next = *(void **)frame;
-	if(!INSTACK(next) || !ISALIGNED(next) || next <= frame)
+	if(!INSTACK(next) || !INALTSTACK(next) || !ISALIGNED(next) || next <= frame)
 	    return;
 	frame = next;
     }