runtime: windows/arm fix tracebacks printed from sigpanic

The exception handler modifies the stack and continuation context so
it looks like the faulting code calls sigpanic() directly. The call was
not set up correctly on ARM, because it did not handle the link register
correctly. This change handles the link register correctly for ARM.

Updates #28854

Change-Id: I7ccf838adfc05cd968a5edd7d19ebba6a2478360
Reviewed-on: https://go-review.googlesource.com/c/150957
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

4 files changed, 22 insertions, 11 deletions

diff --git a/src/runtime/defs_windows_386.go b/src/runtime/defs_windows_386.go
index 38b30b70e3..8c0d6d8b98 100644
--- a/src/runtime/defs_windows_386.go
+++ b/src/runtime/defs_windows_386.go
@@ -105,10 +105,11 @@ func (c *context) ip() uintptr { return uintptr(c.eip) }
 func (c *context) sp() uintptr { return uintptr(c.esp) }
 
 // 386 does not have link register, so this returns 0.
-func (c *context) lr() uintptr { return 0 }
+func (c *context) lr() uintptr      { return 0 }
+func (c *context) set_lr(x uintptr) {}
 
-func (c *context) setip(x uintptr) { c.eip = uint32(x) }
-func (c *context) setsp(x uintptr) { c.esp = uint32(x) }
+func (c *context) set_ip(x uintptr) { c.eip = uint32(x) }
+func (c *context) set_sp(x uintptr) { c.esp = uint32(x) }
 
 func dumpregs(r *context) {
 	print("eax     ", hex(r.eax), "\n")
diff --git a/src/runtime/defs_windows_amd64.go b/src/runtime/defs_windows_amd64.go
index 37508c09be..42a446d3cd 100644
--- a/src/runtime/defs_windows_amd64.go
+++ b/src/runtime/defs_windows_amd64.go
@@ -120,10 +120,11 @@ func (c *context) ip() uintptr { return uintptr(c.rip) }
 func (c *context) sp() uintptr { return uintptr(c.rsp) }
 
 // Amd64 does not have link register, so this returns 0.
-func (c *context) lr() uintptr { return 0 }
+func (c *context) lr() uintptr      { return 0 }
+func (c *context) set_lr(x uintptr) {}
 
-func (c *context) setip(x uintptr) { c.rip = uint64(x) }
-func (c *context) setsp(x uintptr) { c.rsp = uint64(x) }
+func (c *context) set_ip(x uintptr) { c.rip = uint64(x) }
+func (c *context) set_sp(x uintptr) { c.rsp = uint64(x) }
 
 func dumpregs(r *context) {
 	print("rax     ", hex(r.rax), "\n")
diff --git a/src/runtime/defs_windows_arm.go b/src/runtime/defs_windows_arm.go
index 1140f61651..049f5b613a 100644
--- a/src/runtime/defs_windows_arm.go
+++ b/src/runtime/defs_windows_arm.go
@@ -104,8 +104,9 @@ func (c *context) ip() uintptr { return uintptr(c.pc) }
 func (c *context) sp() uintptr { return uintptr(c.spr) }
 func (c *context) lr() uintptr { return uintptr(c.lrr) }
 
-func (c *context) setip(x uintptr) { c.pc = uint32(x) }
-func (c *context) setsp(x uintptr) { c.spr = uint32(x) }
+func (c *context) set_ip(x uintptr) { c.pc = uint32(x) }
+func (c *context) set_sp(x uintptr) { c.spr = uint32(x) }
+func (c *context) set_lr(x uintptr) { c.lrr = uint32(x) }
 
 func dumpregs(r *context) {
 	print("r0   ", hex(r.r0), "\n")
diff --git a/src/runtime/signal_windows.go b/src/runtime/signal_windows.go
index e8a64da657..e6a75a160f 100644
--- a/src/runtime/signal_windows.go
+++ b/src/runtime/signal_windows.go
@@ -117,10 +117,18 @@ func exceptionhandler(info *exceptionrecord, r *context, gp *g) int32 {
 	if r.ip() != 0 {
 		sp := unsafe.Pointer(r.sp())
 		sp = add(sp, ^(unsafe.Sizeof(uintptr(0)) - 1)) // sp--
-		*((*uintptr)(sp)) = r.ip()
-		r.setsp(uintptr(sp))
+		r.set_sp(uintptr(sp))
+		switch GOARCH {
+		default:
+			panic("unsupported architecture")
+		case "386", "amd64":
+			*((*uintptr)(sp)) = r.ip()
+		case "arm":
+			*((*uintptr)(sp)) = r.lr()
+			r.set_lr(r.ip())
+		}
 	}
-	r.setip(funcPC(sigpanic))
+	r.set_ip(funcPC(sigpanic))
 	return _EXCEPTION_CONTINUE_EXECUTION
 }