runtime: handle gdb breakpoint in x86 traceback

This lets stack splits work correctly when running under gdb
when gdb has inserted a breakpoint somewhere on the call
stack.

Fixes #6834.

R=golang-codereviews, minux.ma
CC=golang-codereviews
https://golang.org/cl/48650043

diff --git a/src/pkg/runtime/sys_x86.c b/src/pkg/runtime/sys_x86.c
index e68ff514a224de31906107e801ea1325106f2051..bddfb8a889376d4226a37e20cf3af54e6f4c5b0e 100644 (file)
--- a/src/pkg/runtime/sys_x86.c
+++ b/src/pkg/runtime/sys_x86.c
@@ -27,7 +27,8 @@ void
 runtime·rewindmorestack(Gobuf *gobuf)
 {
        byte *pc;
-       
+       Func *f;
+
        pc = (byte*)gobuf->pc;
        if(pc[0] == 0xe9) { // jmp 4-byte offset
                gobuf->pc = gobuf->pc + 5 + *(int32*)(pc+1);
@@ -37,6 +38,13 @@ runtime·rewindmorestack(Gobuf *gobuf)
                gobuf->pc = gobuf->pc + 2 + *(int8*)(pc+1);
                return;
        }
+       if(pc[0] == 0xcc) { // breakpoint inserted by gdb
+               f = runtime·findfunc(gobuf->pc);
+               if(f != nil) {
+                       gobuf->pc = f->entry;
+                       return;
+               }
+       }
        runtime·printf("runtime: pc=%p %x %x %x %x %x\n", pc, pc[0], pc[1], pc[2], pc[3], pc[4]);
        runtime·throw("runtime: misuse of rewindmorestack");
 }