[release-branch.go1.18] runtime: mark morestack_noctxt SPWRITE on LR …

…architectures

On LR architectures, morestack (and morestack_noctxt) are called
with a special calling convention, where the caller doesn't save
LR on stack but passes it as a register, which morestack will save
to g.sched.lr. The stack unwinder currently doesn't understand it,
and would fail to unwind from it. morestack already writes SP (as
it switches stack), but morestack_noctxt (which tailcalls
morestack) doesn't. If a profiling signal lands right in
morestack_noctxt, the unwinder will try to unwind the stack and
go off, and possibly crash.

Marking morestack_noctxt SPWRITE stops the unwinding.

Ideally we could teach the unwinder about the special calling
convention, or change the calling convention to be less special
(so the unwinder doesn't need to fetch a register from the signal
context). This is a stop-gap solution, to stop the unwinder from
crashing.

Updates #54332.
Fixes #54674.

Change-Id: I75295f2e27ddcf05f1ea0b541aedcb9000ae7576
Reviewed-on: https://go-review.googlesource.com/c/go/+/425396
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
(cherry picked from commit e4be2ac)
Reviewed-on: https://go-review.googlesource.com/c/go/+/425616

src/runtime/asm_arm.s

@@ -387,6 +387,13 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 	RET
 
 TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
+	// Force SPWRITE. This function doesn't actually write SP,
+	// but it is called with a special calling convention where
+	// the caller doesn't save LR on stack but passes it as a
+	// register (R3), and the unwinder currently doesn't understand.
+	// Make it SPWRITE to stop unwinding. (See issue 54332)
+	MOVW	R13, R13
+
 	MOVW	$0, R7
 	B runtime·morestack(SB)
 

src/runtime/asm_arm64.s

@@ -318,6 +318,13 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 	UNDEF
 
 TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
+	// Force SPWRITE. This function doesn't actually write SP,
+	// but it is called with a special calling convention where
+	// the caller doesn't save LR on stack but passes it as a
+	// register (R3), and the unwinder currently doesn't understand.
+	// Make it SPWRITE to stop unwinding. (See issue 54332)
+	MOVD	RSP, RSP
+
 	MOVW	$0, R26
 	B runtime·morestack(SB)
 

src/runtime/asm_mips64x.s

@@ -258,6 +258,13 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 	UNDEF
 
 TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
+	// Force SPWRITE. This function doesn't actually write SP,
+	// but it is called with a special calling convention where
+	// the caller doesn't save LR on stack but passes it as a
+	// register (R3), and the unwinder currently doesn't understand.
+	// Make it SPWRITE to stop unwinding. (See issue 54332)
+	MOVV	R29, R29
+
 	MOVV	R0, REGCTXT
 	JMP	runtime·morestack(SB)
 

src/runtime/asm_mipsx.s

@@ -257,6 +257,13 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 	UNDEF
 
 TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
+	// Force SPWRITE. This function doesn't actually write SP,
+	// but it is called with a special calling convention where
+	// the caller doesn't save LR on stack but passes it as a
+	// register (R3), and the unwinder currently doesn't understand.
+	// Make it SPWRITE to stop unwinding. (See issue 54332)
+	MOVW	R29, R29
+
 	MOVW	R0, REGCTXT
 	JMP	runtime·morestack(SB)
 

src/runtime/asm_ppc64x.s

@@ -338,6 +338,13 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 	UNDEF
 
 TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
+	// Force SPWRITE. This function doesn't actually write SP,
+	// but it is called with a special calling convention where
+	// the caller doesn't save LR on stack but passes it as a
+	// register (R5), and the unwinder currently doesn't understand.
+	// Make it SPWRITE to stop unwinding. (See issue 54332)
+	MOVD	R1, R1
+
 	MOVD	R0, R11
 	BR	runtime·morestack(SB)
 

src/runtime/asm_riscv64.s

@@ -158,8 +158,8 @@ TEXT runtime·getcallerpc(SB),NOSPLIT|NOFRAME,$0-8
  */
 
 // Called during function prolog when more stack is needed.
-// Caller has already loaded:
-// R1: framesize, R2: argsize, R3: LR
+// Called with return address (i.e. caller's PC) in X5 (aka T0),
+// and the LR register contains the caller's LR.
 //
 // The traceback routines see morestack on a g0 as being
 // the top of a stack (for example, morestack calling newstack
@@ -209,6 +209,13 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 
 // func morestack_noctxt()
 TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
+	// Force SPWRITE. This function doesn't actually write SP,
+	// but it is called with a special calling convention where
+	// the caller doesn't save LR on stack but passes it as a
+	// register, and the unwinder currently doesn't understand.
+	// Make it SPWRITE to stop unwinding. (See issue 54332)
+	MOV	X2, X2
+
 	MOV	ZERO, CTXT
 	JMP	runtime·morestack(SB)
 

src/runtime/asm_s390x.s

@@ -346,6 +346,13 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 	UNDEF
 
 TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
+	// Force SPWRITE. This function doesn't actually write SP,
+	// but it is called with a special calling convention where
+	// the caller doesn't save LR on stack but passes it as a
+	// register (R5), and the unwinder currently doesn't understand.
+	// Make it SPWRITE to stop unwinding. (See issue 54332)
+	MOVD	R15, R15
+
 	MOVD	$0, R12
 	BR	runtime·morestack(SB)