rt: Use a DWARF CFI scheme that works on mac in __morestack

Author: brson

src/rt/arch/i386/morestack.S

@@ -53,8 +53,8 @@ MORESTACK:
 
 	pushl %ebp
 #if defined(__linux__) || defined(__APPLE__)
-	.cfi_def_cfa_offset 8
-	.cfi_offset %ebp, -8
+	.cfi_def_cfa_offset 20
+	.cfi_offset %ebp, -20
 #endif
 	movl %esp, %ebp
 #if defined(__linux__) || defined(__APPLE__)
@@ -79,16 +79,6 @@ MORESTACK:
 	testl %eax,%eax
 	jz .L$bail
 
-	// During unwinding we want to skip our caller.
-#if defined(__linux__) || defined(__APPLE__)
-	// Don't understand this line. I think it means that
-	// the next frame's pc is the return address of our caller.
-	.cfi_offset 8, 8
-	// The next frame's esp is stored at our CFA - 12
-	// (by the code below)
-	.cfi_offset %esp, -12
-#endif
-
 	// Save the the correct %esp value for our grandparent frame,
 	// for the unwinder
 	leal 20(%ebp), %eax
@@ -156,7 +146,7 @@ MORESTACK:
 	popl %ebp
 #if defined(__linux__) || defined(__APPLE__)
 	.cfi_restore %ebp
-	.cfi_def_cfa %esp, 4
+	.cfi_def_cfa %esp, 16
 #endif
 	retl $8
 

src/rt/arch/x86_64/morestack.S

@@ -54,19 +54,11 @@ MORESTACK:
 
 	// Set up a normal backtrace
 	pushq %rbp
-	.cfi_def_cfa_offset 16
-	.cfi_offset %rbp, -16
+	.cfi_def_cfa_offset 24
+	.cfi_offset %rbp, -24
 	movq %rsp, %rbp
 	.cfi_def_cfa_register %rbp
 
-	// During unwinding we want to skip our caller since it's not
-	// a complete frame and will make the unwinder sad
-	// Don't understand this line
-	.cfi_offset 16, 0
-	// Tell the unwinding where to get the stack pointer for
-	// our grandparent frame
-	.cfi_offset %rsp, -24
-
 	// Save the grandparent stack pointer for the unwinder
 	leaq 24(%rbp), %rax
 	pushq %rax
@@ -140,7 +132,7 @@ MORESTACK:
 	addq $8, %rsp
 	popq %rbp
 	.cfi_restore %rbp
-	.cfi_def_cfa %rsp, 8
+	.cfi_def_cfa %rsp, 16
 	ret
 
 	.cfi_endproc

src/test/run-fail/morestack4.rs

@@ -0,0 +1,28 @@
+// xfail-test
+// error-pattern:explicit failure
+// compile-flags:--stack-growth
+
+// Just testing unwinding
+
+use std;
+
+native mod rustrt {
+    fn set_min_stack(size: uint);
+}
+
+fn getbig_and_fail(&&i: int) {
+    let r = and_then_get_big_again(@0);
+    if i != 0 {
+        getbig_and_fail(i - 1);
+    } else {
+        fail;
+    }
+}
+
+resource and_then_get_big_again(_i: @int) {
+}
+
+fn main() {
+    rustrt::set_min_stack(256u);
+    task::spawn(1, getbig_and_fail);
+}