runtime: align stack pointer in sigfwd

sigfwd calls an arbitrary C signal handler function.  The System V ABI
for x86_64 (and the most recent revision of the ABI for i386) requires
the stack to be 16-byte aligned.

Fixes: #17641

Change-Id: I77f53d4a8c29c1b0fe8cfbcc8d5381c4e6f75a6b
Reviewed-on: https://go-review.googlesource.com/32107
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testcarchive/main2.c

@@ -7,8 +7,10 @@
 
 #include <setjmp.h>
 #include <signal.h>
+#include <stdarg.h>
 #include <stddef.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>
@@ -46,11 +48,22 @@ static void ioHandler(int signo, siginfo_t* info, void* ctxt) {
 static jmp_buf jmp;
 static char* nullPointer;
 
+// An arbitrary function which requires proper stack alignment; see
+// http://golang.org/issue/17641.
+static void callWithVarargs(void* dummy, ...) {
+	va_list args;
+	va_start(args, dummy);
+	va_end(args);
+}
+
 // Signal handler for SIGSEGV on a C thread.
 static void segvHandler(int signo, siginfo_t* info, void* ctxt) {
 	sigset_t mask;
 	int i;
 
+	// Call an arbitrary function that requires the stack to be properly aligned.
+	callWithVarargs("dummy arg", 3.1415);
+
 	if (sigemptyset(&mask) < 0) {
 		die("sigemptyset");
 	}

src/runtime/sys_darwin_386.s

@@ -254,12 +254,12 @@ TEXT runtime·sigfwd(SB),NOSPLIT,$0-16
 	MOVL	info+8(FP), CX
 	MOVL	ctx+12(FP), DX
 	MOVL	SP, SI
-	SUBL	$32, SP		// align stack; handler might be C code
+	SUBL	$32, SP
-	ANDL	$~15, SP
+	ANDL	$~15, SP	// align stack: handler might be a C function
 	MOVL	BX, 0(SP)
 	MOVL	CX, 4(SP)
 	MOVL	DX, 8(SP)
-	MOVL	SI, 12(SP)
+	MOVL	SI, 12(SP)	// save SI: handler might be a Go function
 	CALL	AX
 	MOVL	12(SP), AX
 	MOVL	AX, SP

src/runtime/sys_darwin_amd64.s

@@ -219,15 +219,16 @@ TEXT runtime·sigaction(SB),NOSPLIT,$0-24
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
-	MOVQ fn+0(FP),    AX
+	MOVQ	fn+0(FP),    AX
-	MOVL sig+8(FP),   DI
+	MOVL	sig+8(FP),   DI
-	MOVQ info+16(FP), SI
+	MOVQ	info+16(FP), SI
-	MOVQ ctx+24(FP),  DX
+	MOVQ	ctx+24(FP),  DX
-	MOVQ SP, BP
+	PUSHQ	BP
-	SUBQ $64, SP
+	MOVQ	SP, BP
-	ANDQ $~15, SP     // alignment for x86_64 ABI
+	ANDQ	$~15, SP     // alignment for x86_64 ABI
-	CALL AX
+	CALL	AX
-	MOVQ BP, SP
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$32

src/runtime/sys_dragonfly_amd64.s

@@ -188,11 +188,16 @@ TEXT runtime·sigaction(SB),NOSPLIT,$-8
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
-	MOVL	sig+8(FP), DI
+	MOVQ	fn+0(FP),    AX
+	MOVL	sig+8(FP),   DI
 	MOVQ	info+16(FP), SI
-	MOVQ	ctx+24(FP), DX
+	MOVQ	ctx+24(FP),  DX
-	MOVQ	fn+0(FP), AX
+	PUSHQ	BP
+	MOVQ	SP, BP
+	ANDQ	$~15, SP     // alignment for x86_64 ABI
 	CALL	AX
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$24

src/runtime/sys_freebsd_386.s

@@ -208,14 +208,20 @@ TEXT runtime·sigaction(SB),NOSPLIT,$-4
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$12-16
-	MOVL	sig+4(FP), AX
-	MOVL	AX, 0(SP)
-	MOVL	info+8(FP), AX
-	MOVL	AX, 4(SP)
-	MOVL	ctx+12(FP), AX
-	MOVL	AX, 8(SP)
 	MOVL	fn+0(FP), AX
+	MOVL	sig+4(FP), BX
+	MOVL	info+8(FP), CX
+	MOVL	ctx+12(FP), DX
+	MOVL	SP, SI
+	SUBL	$32, SP
+	ANDL	$~15, SP	// align stack: handler might be a C function
+	MOVL	BX, 0(SP)
+	MOVL	CX, 4(SP)
+	MOVL	DX, 8(SP)
+	MOVL	SI, 12(SP)	// save SI: handler might be a Go function
 	CALL	AX
+	MOVL	12(SP), AX
+	MOVL	AX, SP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$12

src/runtime/sys_freebsd_amd64.s

@@ -184,11 +184,16 @@ TEXT runtime·sigaction(SB),NOSPLIT,$-8
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
-	MOVL	sig+8(FP), DI
+	MOVQ	fn+0(FP),    AX
+	MOVL	sig+8(FP),   DI
 	MOVQ	info+16(FP), SI
-	MOVQ	ctx+24(FP), DX
+	MOVQ	ctx+24(FP),  DX
-	MOVQ	fn+0(FP), AX
+	PUSHQ	BP
+	MOVQ	SP, BP
+	ANDQ	$~15, SP     // alignment for x86_64 ABI
 	CALL	AX
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$24

src/runtime/sys_linux_386.s

@@ -212,14 +212,20 @@ TEXT runtime·rt_sigaction(SB),NOSPLIT,$0
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$12-16
-	MOVL	sig+4(FP), AX
-	MOVL	AX, 0(SP)
-	MOVL	info+8(FP), AX
-	MOVL	AX, 4(SP)
-	MOVL	ctx+12(FP), AX
-	MOVL	AX, 8(SP)
 	MOVL	fn+0(FP), AX
+	MOVL	sig+4(FP), BX
+	MOVL	info+8(FP), CX
+	MOVL	ctx+12(FP), DX
+	MOVL	SP, SI
+	SUBL	$32, SP
+	ANDL	$-15, SP	// align stack: handler might be a C function
+	MOVL	BX, 0(SP)
+	MOVL	CX, 4(SP)
+	MOVL	DX, 8(SP)
+	MOVL	SI, 12(SP)	// save SI: handler might be a Go function
 	CALL	AX
+	MOVL	12(SP), AX
+	MOVL	AX, SP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$12

src/runtime/sys_linux_amd64.s

@@ -219,11 +219,16 @@ TEXT runtime·rt_sigaction(SB),NOSPLIT,$0-36
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
-	MOVL	sig+8(FP), DI
+	MOVQ	fn+0(FP),    AX
+	MOVL	sig+8(FP),   DI
 	MOVQ	info+16(FP), SI
-	MOVQ	ctx+24(FP), DX
+	MOVQ	ctx+24(FP),  DX
-	MOVQ	fn+0(FP), AX
+	PUSHQ	BP
+	MOVQ	SP, BP
+	ANDQ	$~15, SP     // alignment for x86_64 ABI
 	CALL	AX
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$24

src/runtime/sys_netbsd_386.s

@@ -216,14 +216,20 @@ TEXT runtime·sigaction(SB),NOSPLIT,$24
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$12-16
-	MOVL	sig+4(FP), AX
-	MOVL	AX, 0(SP)
-	MOVL	info+8(FP), AX
-	MOVL	AX, 4(SP)
-	MOVL	ctx+12(FP), AX
-	MOVL	AX, 8(SP)
 	MOVL	fn+0(FP), AX
+	MOVL	sig+4(FP), BX
+	MOVL	info+8(FP), CX
+	MOVL	ctx+12(FP), DX
+	MOVL	SP, SI
+	SUBL	$32, SP
+	ANDL	$-15, SP	// align stack: handler might be a C function
+	MOVL	BX, 0(SP)
+	MOVL	CX, 4(SP)
+	MOVL	DX, 8(SP)
+	MOVL	SI, 12(SP)	// save SI: handler might be a Go function
 	CALL	AX
+	MOVL	12(SP), AX
+	MOVL	AX, SP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$12

src/runtime/sys_netbsd_amd64.s

@@ -238,11 +238,16 @@ TEXT runtime·sigaction(SB),NOSPLIT,$-8
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
-	MOVL	sig+8(FP), DI
+	MOVQ	fn+0(FP),    AX
+	MOVL	sig+8(FP),   DI
 	MOVQ	info+16(FP), SI
-	MOVQ	ctx+24(FP), DX
+	MOVQ	ctx+24(FP),  DX
-	MOVQ	fn+0(FP), AX
+	PUSHQ	BP
+	MOVQ	SP, BP
+	ANDQ	$~15, SP     // alignment for x86_64 ABI
 	CALL	AX
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$32

src/runtime/sys_openbsd_386.s

@@ -196,14 +196,20 @@ TEXT runtime·obsdsigprocmask(SB),NOSPLIT,$-4
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$12-16
-	MOVL	sig+4(FP), AX
-	MOVL	AX, 0(SP)
-	MOVL	info+8(FP), AX
-	MOVL	AX, 4(SP)
-	MOVL	ctx+12(FP), AX
-	MOVL	AX, 8(SP)
 	MOVL	fn+0(FP), AX
+	MOVL	sig+4(FP), BX
+	MOVL	info+8(FP), CX
+	MOVL	ctx+12(FP), DX
+	MOVL	SP, SI
+	SUBL	$32, SP
+	ANDL	$~15, SP	// align stack: handler might be a C function
+	MOVL	BX, 0(SP)
+	MOVL	CX, 4(SP)
+	MOVL	DX, 8(SP)
+	MOVL	SI, 12(SP)	// save SI: handler might be a Go function
 	CALL	AX
+	MOVL	12(SP), AX
+	MOVL	AX, SP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$12

src/runtime/sys_openbsd_amd64.s

@@ -229,11 +229,16 @@ TEXT runtime·obsdsigprocmask(SB),NOSPLIT,$0
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
-	MOVL	sig+8(FP), DI
+	MOVQ	fn+0(FP),    AX
+	MOVL	sig+8(FP),   DI
 	MOVQ	info+16(FP), SI
-	MOVQ	ctx+24(FP), DX
+	MOVQ	ctx+24(FP),  DX
-	MOVQ	fn+0(FP), AX
+	PUSHQ	BP
+	MOVQ	SP, BP
+	ANDQ	$~15, SP     // alignment for x86_64 ABI
 	CALL	AX
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 TEXT runtime·sigtramp(SB),NOSPLIT,$24

src/runtime/sys_solaris_amd64.s

@@ -290,11 +290,16 @@ exit:
 	RET
 
 TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
-	MOVL	sig+8(FP), DI
+	MOVQ	fn+0(FP),    AX
+	MOVL	sig+8(FP),   DI
 	MOVQ	info+16(FP), SI
-	MOVQ	ctx+24(FP), DX
+	MOVQ	ctx+24(FP),  DX
-	MOVQ	fn+0(FP), AX
+	PUSHQ	BP
+	MOVQ	SP, BP
+	ANDQ	$~15, SP     // alignment for x86_64 ABI
 	CALL	AX
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 // Called from runtime·usleep (Go). Can be called on Go stack, on OS stack,