From 32b770b2c05d69c41f0ab6719dc028cf4c79e334 Mon Sep 17 00:00:00 2001
From: Keith Randall <khr@golang.org>
Date: Thu, 29 Aug 2013 15:53:34 -0700
Subject: [PATCH] runtime: jump to badmcall instead of calling it. This
 replaces the mcall frame with the badmcall frame instead of leaving the mcall
 frame on the stack and adding the badmcall frame. Because mcall is no longer
 on the stack, traceback will now report what called mcall, which is what we
 would like to see in this situation.

R=golang-dev, cshapiro
CC=golang-dev
https://golang.org/cl/13012044
---
 src/pkg/runtime/asm_386.s   | 8 +++++---
 src/pkg/runtime/asm_amd64.s | 8 ++++----
 src/pkg/runtime/asm_arm.s   | 5 +++--
 src/pkg/runtime/proc.c      | 6 ++++--
 4 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/pkg/runtime/asm_386.s b/src/pkg/runtime/asm_386.s
index c61b75cfb22..79f2e79296c 100644
--- a/src/pkg/runtime/asm_386.s
+++ b/src/pkg/runtime/asm_386.s
@@ -181,14 +181,16 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-4
 	MOVL	m(CX), BX
 	MOVL	m_g0(BX), SI
 	CMPL	SI, AX	// if g == m->g0 call badmcall
-	JNE	2(PC)
-	CALL	runtime·badmcall(SB)
+	JNE	3(PC)
+	MOVL	$runtime·badmcall(SB), AX
+	JMP	AX
 	MOVL	SI, g(CX)	// g = m->g0
 	MOVL	(g_sched+gobuf_sp)(SI), SP	// sp = m->g0->sched.sp
 	PUSHL	AX
 	CALL	DI
 	POPL	AX
-	CALL	runtime·badmcall2(SB)
+	MOVL	$runtime·badmcall2(SB), AX
+	JMP	AX
 	RET
 
 /*
diff --git a/src/pkg/runtime/asm_amd64.s b/src/pkg/runtime/asm_amd64.s
index fcc75a9229d..a85056c9eae 100644
--- a/src/pkg/runtime/asm_amd64.s
+++ b/src/pkg/runtime/asm_amd64.s
@@ -169,16 +169,16 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-8
 	MOVQ	m_g0(BX), SI
 	CMPQ	SI, AX	// if g == m->g0 call badmcall
 	JNE	3(PC)
-	ARGSIZE(0)
-	CALL	runtime·badmcall(SB)
+	MOVQ	$runtime·badmcall(SB), AX
+	JMP	AX
 	MOVQ	SI, g(CX)	// g = m->g0
 	MOVQ	(g_sched+gobuf_sp)(SI), SP	// sp = m->g0->sched.sp
 	PUSHQ	AX
 	ARGSIZE(8)
 	CALL	DI
 	POPQ	AX
-	ARGSIZE(0)
-	CALL	runtime·badmcall2(SB)
+	MOVQ	$runtime·badmcall2(SB), AX
+	JMP	AX
 	RET
 
 /*
diff --git a/src/pkg/runtime/asm_arm.s b/src/pkg/runtime/asm_arm.s
index 0d12b6a0d8c..b66f80e2c6d 100644
--- a/src/pkg/runtime/asm_arm.s
+++ b/src/pkg/runtime/asm_arm.s
@@ -157,12 +157,13 @@ TEXT runtime·mcall(SB), NOSPLIT, $-4-4
 	MOVW	g, R1
 	MOVW	m_g0(m), g
 	CMP	g, R1
-	BL.EQ	runtime·badmcall(SB)
+	B.NE	2(PC)
+	B	runtime·badmcall(SB)
 	MOVW	(g_sched+gobuf_sp)(g), SP
 	SUB	$8, SP
 	MOVW	R1, 4(SP)
 	BL	(R0)
-	BL	runtime·badmcall2(SB)
+	B	runtime·badmcall2(SB)
 	RET
 
 /*
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index dab62ad69be..d37014f3a51 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -1997,14 +1997,16 @@ runtime·mcount(void)
 }
 
 void
-runtime·badmcall(void)  // called from assembly
+runtime·badmcall(void (*fn)(G*))  // called from assembly
 {
+	USED(fn); // TODO: print fn?
 	runtime·throw("runtime: mcall called on m->g0 stack");
 }
 
 void
-runtime·badmcall2(void)  // called from assembly
+runtime·badmcall2(void (*fn)(G*))  // called from assembly
 {
+	USED(fn);
 	runtime·throw("runtime: mcall function returned");
 }