runtime: fix build on non-x86 machines

Fixes #11656 (again).

Change-Id: I170ff10bfbdb0f34e57c11de42b6ee5291837813
Reviewed-on: https://go-review.googlesource.com/12142Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/signal_arm.go

@@ -67,11 +67,21 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 		c.set_sp(sp)
 		*(*uint32)(unsafe.Pointer(uintptr(sp))) = c.lr()
 
+		pc := uintptr(gp.sigpc)
+
+		// If we don't recognize the PC as code
+		// but we do recognize the link register as code,
+		// then assume this was a call to non-code and treat like
+		// pc == 0, to make unwinding show the context.
+		if pc != 0 && findfunc(pc) == nil && findfunc(uintptr(c.lr())) != nil {
+			pc = 0
+		}
+
 		// Don't bother saving PC if it's zero, which is
 		// probably a call to a nil func: the old link register
 		// is more useful in the stack trace.
-		if gp.sigpc != 0 {
-			c.set_lr(uint32(gp.sigpc))
+		if pc != 0 {
+			c.set_lr(uint32(pc))
 		}
 
 		// In case we are panicking from external C code

src/runtime/signal_arm64.go

@@ -80,11 +80,21 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 		c.set_sp(sp)
 		*(*uint64)(unsafe.Pointer(uintptr(sp))) = c.lr()
 
+		pc := uintptr(gp.sigpc)
+
+		// If we don't recognize the PC as code
+		// but we do recognize the link register as code,
+		// then assume this was a call to non-code and treat like
+		// pc == 0, to make unwinding show the context.
+		if pc != 0 && findfunc(pc) == nil && findfunc(uintptr(c.lr())) != nil {
+			pc = 0
+		}
+
 		// Don't bother saving PC if it's zero, which is
 		// probably a call to a nil func: the old link register
 		// is more useful in the stack trace.
-		if gp.sigpc != 0 {
-			c.set_lr(uint64(gp.sigpc))
+		if pc != 0 {
+			c.set_lr(uint64(pc))
 		}
 
 		// In case we are panicking from external C code

src/runtime/signal_ppc64x.go

@@ -84,11 +84,21 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 		c.set_sp(sp)
 		*(*uint64)(unsafe.Pointer(uintptr(sp))) = c.link()
 
+		pc := uintptr(gp.sigpc)
+
+		// If we don't recognize the PC as code
+		// but we do recognize the link register as code,
+		// then assume this was a call to non-code and treat like
+		// pc == 0, to make unwinding show the context.
+		if pc != 0 && findfunc(pc) == nil && findfunc(uintptr(c.link())) != nil {
+			pc = 0
+		}
+
 		// Don't bother saving PC if it's zero, which is
 		// probably a call to a nil func: the old link register
 		// is more useful in the stack trace.
-		if gp.sigpc != 0 {
-			c.set_link(uint64(gp.sigpc))
+		if pc != 0 {
+			c.set_link(uint64(pc))
 		}
 
 		// In case we are panicking from external C code