runtime: pass to signal handler value of g at time of signal

The existing code assumed that signals only arrived
while executing on the goroutine stack (g == m->curg),
not while executing on the scheduler stack (g == m->g0).

Most of the signal handling trampolines correctly saved
and restored g already, but the sighandler C code did not
have access to it.

Some rewriting of assembly to make the various
implementations as similar as possible.

Will need to change Windows too but I don't
understand how sigtramp gets called there.

R=r
CC=golang-dev
https://golang.org/cl/4203042

src/pkg/runtime/darwin/386/signal.c

@@ -34,20 +34,19 @@ runtime·signame(int32 sig)
 }
 
 void
-runtime·sighandler(int32 sig, Siginfo *info, void *context)
+runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 {
 	Ucontext *uc;
 	Mcontext *mc;
 	Regs *r;
 	uintptr *sp;
-	G *gp;
 	byte *pc;
 
 	uc = context;
 	mc = uc->uc_mcontext;
 	r = &mc->ss;
 
-	if((gp = m->curg) != nil && (runtime·sigtab[sig].flags & SigPanic)) {
+	if(gp != nil && (runtime·sigtab[sig].flags & SigPanic)) {
 		// Work around Leopard bug that doesn't set FPE_INTDIV.
 		// Look at instruction to see if it is a divide.
 		// Not necessary in Snow Leopard (si_code will be != 0).
@@ -103,8 +102,8 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context)
 	runtime·printf("\n");
 
 	if(runtime·gotraceback()){
-		runtime·traceback((void*)r->eip, (void*)r->esp, 0, m->curg);
-		runtime·tracebackothers(m->curg);
+		runtime·traceback((void*)r->eip, (void*)r->esp, 0, gp);
+		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 

src/pkg/runtime/darwin/386/sys.s

@@ -80,33 +80,34 @@ TEXT runtime·sigtramp(SB),7,$40
 	get_tls(CX)
 
 	// save g
-	MOVL	g(CX), BP
-	MOVL	BP, 20(SP)
+	MOVL	g(CX), DI
+	MOVL	DI, 20(SP)
 	
 	// g = m->gsignal
 	MOVL	m(CX), BP
 	MOVL	m_gsignal(BP), BP
 	MOVL	BP, g(CX)
 
-	MOVL	handler+0(FP), DI
-	// 4(FP) is sigstyle
-	MOVL	signo+8(FP), AX
-	MOVL	siginfo+12(FP), BX
-	MOVL	context+16(FP), CX
-
-	MOVL	AX, 0(SP)
+	// copy arguments to sighandler
+	MOVL	sig+8(FP), BX
+	MOVL	BX, 0(SP)
+	MOVL	info+12(FP), BX
 	MOVL	BX, 4(SP)
-	MOVL	CX, 8(SP)
-	CALL	DI
+	MOVL	context+16(FP), BX
+	MOVL	BX, 8(SP)
+	MOVL	DI, 12(SP)
+	
+	MOVL	handler+0(FP), BX
+	CALL	BX
 
 	// restore g
 	get_tls(CX)
-	MOVL	20(SP), BP
-	MOVL	BP, g(CX)
+	MOVL	20(SP), DI
+	MOVL	DI, g(CX)
 
+	// call sigreturn
 	MOVL	context+16(FP), CX
 	MOVL	style+4(FP), BX
-
 	MOVL	$0, 0(SP)	// "caller PC" - ignored
 	MOVL	CX, 4(SP)
 	MOVL	BX, 8(SP)

src/pkg/runtime/darwin/amd64/signal.c

@@ -42,12 +42,11 @@ runtime·signame(int32 sig)
 }
 
 void
-runtime·sighandler(int32 sig, Siginfo *info, void *context)
+runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 {
 	Ucontext *uc;
 	Mcontext *mc;
 	Regs *r;
-	G *gp;
 	uintptr *sp;
 	byte *pc;
 
@@ -55,7 +54,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context)
 	mc = uc->uc_mcontext;
 	r = &mc->ss;
 
-	if((gp = m->curg) != nil && (runtime·sigtab[sig].flags & SigPanic)) {
+	if(gp != nil && (runtime·sigtab[sig].flags & SigPanic)) {
 		// Work around Leopard bug that doesn't set FPE_INTDIV.
 		// Look at instruction to see if it is a divide.
 		// Not necessary in Snow Leopard (si_code will be != 0).
@@ -113,8 +112,8 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context)
 	runtime·printf("\n");
 
 	if(runtime·gotraceback()){
-		runtime·traceback((void*)r->rip, (void*)r->rsp, 0, g);
-		runtime·tracebackothers(g);
+		runtime·traceback((void*)r->rip, (void*)r->rsp, 0, gp);
+		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 

src/pkg/runtime/darwin/amd64/sys.s

@@ -66,8 +66,8 @@ TEXT runtime·sigtramp(SB),7,$64
 	get_tls(BX)
 	
 	// save g
-	MOVQ	g(BX), BP
-	MOVQ	BP, 40(SP)
+	MOVQ	g(BX), R10
+	MOVQ	R10, 48(SP)
 	
 	// g = m->gsignal
 	MOVQ	m(BX), BP
@@ -77,18 +77,21 @@ TEXT runtime·sigtramp(SB),7,$64
 	MOVL	DX, 0(SP)
 	MOVQ	CX, 8(SP)
 	MOVQ	R8, 16(SP)
-	MOVQ	R8, 24(SP)	// save ucontext
-	MOVQ	SI, 32(SP)	// save infostyle
+	MOVQ	R10, 24(SP)
+
+	MOVQ	R8, 32(SP)	// save ucontext
+	MOVQ	SI, 40(SP)	// save infostyle
 	CALL	DI
 
 	// restore g
 	get_tls(BX)
-	MOVQ	40(SP), BP
-	MOVQ	BP, g(BX)
+	MOVQ	48(SP), R10
+	MOVQ	R10, g(BX)
 
+	// call sigreturn
 	MOVL	$(0x2000000+184), AX	// sigreturn(ucontext, infostyle)
-	MOVQ	24(SP), DI	// saved ucontext
-	MOVQ	32(SP), SI	// saved infostyle
+	MOVQ	32(SP), DI	// saved ucontext
+	MOVQ	40(SP), SI	// saved infostyle
 	SYSCALL
 	INT $3	// not reached
 

src/pkg/runtime/freebsd/386/signal.c

@@ -45,17 +45,16 @@ runtime·signame(int32 sig)
 }
 
 void
-runtime·sighandler(int32 sig, Siginfo* info, void* context)
+runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 {
 	Ucontext *uc;
 	Mcontext *r;
-	G *gp;
 	uintptr *sp;
 
 	uc = context;
 	r = &uc->uc_mcontext;
 
-	if((gp = m->curg) != nil && (runtime·sigtab[sig].flags & SigPanic)) {
+	if(gp != nil && (runtime·sigtab[sig].flags & SigPanic)) {
 		// Make it look like a call to the signal func.
 		// Have to pass arguments out of band since
 		// augmenting the stack frame would break
@@ -99,8 +98,8 @@ runtime·sighandler(int32 sig, Siginfo* info, void* context)
 	runtime·printf("\n");
 
 	if(runtime·gotraceback()){
-		runtime·traceback((void*)r->mc_eip, (void*)r->mc_esp, 0, m->curg);
-		runtime·tracebackothers(m->curg);
+		runtime·traceback((void*)r->mc_eip, (void*)r->mc_esp, 0, gp);
+		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 

src/pkg/runtime/freebsd/386/sys.s

@@ -111,30 +111,36 @@ TEXT runtime·sigaction(SB),7,$-4
 	CALL	runtime·notok(SB)
 	RET
 
-TEXT runtime·sigtramp(SB),7,$40
-	// g = m->gsignal
-	get_tls(DX)
-	MOVL	m(DX), BP
-	MOVL	m_gsignal(BP), BP
-	MOVL	BP, g(DX)
+TEXT runtime·sigtramp(SB),7,$44
+	get_tls(CX)
 
-	MOVL	signo+0(FP), AX
-	MOVL	siginfo+4(FP), BX
-	MOVL	context+8(FP), CX
+	// save g
+	MOVL	g(CX), DI
+	MOVL	DI, 20(SP)
+	
+	// g = m->gsignal
+	MOVL	m(CX), BX
+	MOVL	m_gsignal(BX), BX
+	MOVL	BX, g(CX)
 
-	MOVL	AX, 0(SP)
+	// copy arguments for call to sighandler
+	MOVL	signo+0(FP), BX
+	MOVL	BX, 0(SP)
+	MOVL	info+4(FP), BX
 	MOVL	BX, 4(SP)
-	MOVL	CX, 8(SP)
-	CALL	runtime·sighandler(SB)
+	MOVL	context+8(FP), BX
+	MOVL	BX, 8(SP)
+	MOVL	DI, 12(SP)
 
-	// g = m->curg
-	get_tls(DX)
-	MOVL	m(DX), BP
-	MOVL	m_curg(BP), BP
-	MOVL	BP, g(DX)
+	CALL	runtime·sighandler(SB)
 
+	// restore g
+	get_tls(CX)
+	MOVL	20(SP), BX
+	MOVL	BX, g(CX)
+	
+	// call sigreturn
 	MOVL	context+8(FP), AX
-
 	MOVL	$0, 0(SP)	// syscall gap
 	MOVL	AX, 4(SP)
 	MOVL	$417, AX	// sigreturn(ucontext)

src/pkg/runtime/freebsd/amd64/signal.c

@@ -53,17 +53,16 @@ runtime·signame(int32 sig)
 }
 
 void
-runtime·sighandler(int32 sig, Siginfo* info, void* context)
+runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 {
 	Ucontext *uc;
 	Mcontext *r;
-	G *gp;
 	uintptr *sp;
 
 	uc = context;
 	r = &uc->uc_mcontext;
 
-	if((gp = m->curg) != nil && (runtime·sigtab[sig].flags & SigPanic)) {
+	if(gp != nil && (runtime·sigtab[sig].flags & SigPanic)) {
 		// Make it look like a call to the signal func.
 		// Have to pass arguments out of band since
 		// augmenting the stack frame would break
@@ -107,8 +106,8 @@ runtime·sighandler(int32 sig, Siginfo* info, void* context)
 	runtime·printf("\n");
 
 	if(runtime·gotraceback()){
-		runtime·traceback((void*)r->mc_rip, (void*)r->mc_rsp, 0, g);
-		runtime·tracebackothers(g);
+		runtime·traceback((void*)r->mc_rip, (void*)r->mc_rsp, 0, gp);
+		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 

src/pkg/runtime/freebsd/amd64/sys.s

@@ -90,15 +90,29 @@ TEXT runtime·sigaction(SB),7,$-8
 	CALL	runtime·notok(SB)
 	RET
 
-TEXT runtime·sigtramp(SB),7,$24-16
-	get_tls(CX)
-	MOVQ	m(CX), AX
-	MOVQ	m_gsignal(AX), AX
-	MOVQ	AX, g(CX)
+TEXT runtime·sigtramp(SB),7,$64
+	get_tls(BX)
+	
+	// save g
+	MOVQ	g(BX), R10
+	MOVQ	R10, 40(SP)
+	
+	// g = m->signal
+	MOVQ	m(BX), BP
+	MOVQ	m_gsignal(BP), BP
+	MOVQ	BP, g(BX)
+	
 	MOVQ	DI, 0(SP)
 	MOVQ	SI, 8(SP)
 	MOVQ	DX, 16(SP)
+	MOVQ	R10, 24(SP)
+	
 	CALL	runtime·sighandler(SB)
+
+	// restore g
+	get_tls(BX)
+	MOVQ	40(SP), R10
+	MOVQ	R10, g(BX)
 	RET
 
 TEXT runtime·mmap(SB),7,$0

src/pkg/runtime/linux/386/signal.c

@@ -42,17 +42,16 @@ runtime·signame(int32 sig)
 }
 
 void
-runtime·sighandler(int32 sig, Siginfo* info, void* context)
+runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 {
 	Ucontext *uc;
 	Sigcontext *r;
 	uintptr *sp;
-	G *gp;
 
 	uc = context;
 	r = &uc->uc_mcontext;
 
-	if((gp = m->curg) != nil && (runtime·sigtab[sig].flags & SigPanic)) {
+	if(gp != nil && (runtime·sigtab[sig].flags & SigPanic)) {
 		// Make it look like a call to the signal func.
 		// Have to pass arguments out of band since
 		// augmenting the stack frame would break
@@ -96,8 +95,8 @@ runtime·sighandler(int32 sig, Siginfo* info, void* context)
 	runtime·printf("\n");
 
 	if(runtime·gotraceback()){
-		runtime·traceback((void*)r->eip, (void*)r->esp, 0, m->curg);
-		runtime·tracebackothers(m->curg);
+		runtime·traceback((void*)r->eip, (void*)r->esp, 0, gp);
+		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 

src/pkg/runtime/linux/386/sys.s

@@ -56,12 +56,12 @@ TEXT runtime·rt_sigaction(SB),7,$0
 	INT	$0x80
 	RET
 
-TEXT runtime·sigtramp(SB),7,$40
+TEXT runtime·sigtramp(SB),7,$44
 	get_tls(CX)
 	
 	// save g
-	MOVL	g(CX), BX
-	MOVL	BX, 20(SP)
+	MOVL	g(CX), DI
+	MOVL	DI, 20(SP)
 	
 	// g = m->gsignal
 	MOVL	m(CX), BX
@@ -75,6 +75,7 @@ TEXT runtime·sigtramp(SB),7,$40
 	MOVL	BX, 4(SP)
 	MOVL	context+8(FP), BX
 	MOVL	BX, 8(SP)
+	MOVL	DI, 12(SP)
 
 	CALL	runtime·sighandler(SB)
 	

src/pkg/runtime/linux/amd64/signal.c

@@ -50,19 +50,18 @@ runtime·signame(int32 sig)
 }
 
 void
-runtime·sighandler(int32 sig, Siginfo* info, void* context)
+runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 {
 	Ucontext *uc;
 	Mcontext *mc;
 	Sigcontext *r;
 	uintptr *sp;
-	G *gp;
 
 	uc = context;
 	mc = &uc->uc_mcontext;
 	r = (Sigcontext*)mc;	// same layout, more conveient names
 
-	if((gp = m->curg) != nil && (runtime·sigtab[sig].flags & SigPanic)) {
+	if(gp != nil && (runtime·sigtab[sig].flags & SigPanic)) {
 		// Make it look like a call to the signal func.
 		// Have to pass arguments out of band since
 		// augmenting the stack frame would break
@@ -106,8 +105,8 @@ runtime·sighandler(int32 sig, Siginfo* info, void* context)
 	runtime·printf("\n");
 
 	if(runtime·gotraceback()){
-		runtime·traceback((void*)r->rip, (void*)r->rsp, 0, g);
-		runtime·tracebackothers(g);
+		runtime·traceback((void*)r->rip, (void*)r->rsp, 0, gp);
+		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 

src/pkg/runtime/linux/amd64/sys.s

@@ -64,8 +64,8 @@ TEXT runtime·sigtramp(SB),7,$64
 	get_tls(BX)
 
 	// save g
-	MOVQ	g(BX), BP
-	MOVQ	BP, 40(SP)
+	MOVQ	g(BX), R10
+	MOVQ	R10, 40(SP)
 
 	// g = m->gsignal
 	MOVQ	m(BX), BP
@@ -75,12 +75,14 @@ TEXT runtime·sigtramp(SB),7,$64
 	MOVQ	DI, 0(SP)
 	MOVQ	SI, 8(SP)
 	MOVQ	DX, 16(SP)
+	MOVQ	R10, 24(SP)
+
 	CALL	runtime·sighandler(SB)
 
 	// restore g
 	get_tls(BX)
-	MOVQ	40(SP), BP
-	MOVQ	BP, g(BX)
+	MOVQ	40(SP), R10
+	MOVQ	R10, g(BX)
 	RET
 
 TEXT runtime·sigignore(SB),7,$0

src/pkg/runtime/linux/arm/signal.c

@@ -50,16 +50,15 @@ runtime·signame(int32 sig)
 }
 
 void
-runtime·sighandler(int32 sig, Siginfo *info, void *context)
+runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 {
 	Ucontext *uc;
 	Sigcontext *r;
-	G *gp;
 
 	uc = context;
 	r = &uc->uc_mcontext;
 
-	if((gp = m->curg) != nil && (runtime·sigtab[sig].flags & SigPanic)) {
+	if(gp != nil && (runtime·sigtab[sig].flags & SigPanic)) {
 		// Make it look like a call to the signal func.
 		// Have to pass arguments out of band since
 		// augmenting the stack frame would break
@@ -99,8 +98,8 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context)
 	runtime·printf("\n");
 
 	if(runtime·gotraceback()){
-		runtime·traceback((void*)r->arm_pc, (void*)r->arm_sp, (void*)r->arm_lr, m->curg);
-		runtime·tracebackothers(m->curg);
+		runtime·traceback((void*)r->arm_pc, (void*)r->arm_sp, (void*)r->arm_lr, gp);
+		runtime·tracebackothers(gp);
 		runtime·printf("\n");
 		runtime·dumpregs(r);
 	}

src/pkg/runtime/linux/arm/sys.s

@@ -197,11 +197,24 @@ TEXT runtime·sigignore(SB),7,$0
 	RET
 
 TEXT runtime·sigtramp(SB),7,$24
+	// save g
+	MOVW	g, R3
+	MOVW	g, 20(R13)
+	
+	// g = m->gsignal
 	MOVW	m_gsignal(m), g
+
+	// copy arguments for call to sighandler
 	MOVW	R0, 4(R13)
 	MOVW	R1, 8(R13)
 	MOVW	R2, 12(R13)
+	MOVW	R3, 16(R13)
+
 	BL	runtime·sighandler(SB)
+	
+	// restore g
+	MOVW	20(R13), g
+
 	RET
 
 TEXT runtime·rt_sigaction(SB),7,$0