runtime: fix runtime.Breakpoint on ARMv5

Fixes #8775.

Use the illegal instruction suggested by Ian in https://golang.org/cl/144180043/#msg4 on all arm arches.

LGTM=minux
R=golang-codereviews, gobot, rsc
CC=golang-codereviews, iant, minux
https://golang.org/cl/146130043

diff --git a/src/runtime/asm_arm.s b/src/runtime/asm_arm.s
index f67f94939b951da0341b5bacd0dffb41dcc53f95..38d97b78f3afb815e152480be63d18a04d3559f7 100644 (file)
--- a/src/runtime/asm_arm.s
+++ b/src/runtime/asm_arm.s
@@ -96,7 +96,7 @@ TEXT runtime·breakpoint(SB),NOSPLIT,$0-0
 #ifdef GOOS_nacl
        WORD    $0xe125be7f     // BKPT 0x5bef, NACL_INSTR_ARM_BREAKPOINT
 #else
-       WORD    $0xe1200071     // BKPT 0x0001
+       WORD    $0xe7f001f0     // undefined instruction that gdb understands is a software breakpoint
 #endif
        RET