9 files changed, 39 insertions, 29 deletions
diff --git a/src/runtime/asm_386.s b/src/runtime/asm_386.s
index 11c60309f4..571aa28a9e 100644
--- a/src/runtime/asm_386.s
+++ b/src/runtime/asm_386.s
@@ -633,18 +633,18 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-12
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	get_tls(CX)
-	MOVL	g(CX), BP
-	CMPL	BP, $0
-	JEQ	nosave	// Don't even have a G yet.
-	MOVL	g_m(BP), BP
-	MOVL	m_g0(BP), SI
 	MOVL	g(CX), DI
-	CMPL	SI, DI
-	JEQ	noswitch
+	CMPL	DI, $0
+	JEQ	nosave	// Don't even have a G yet.
+	MOVL	g_m(DI), BP
 	CMPL	DI, m_gsignal(BP)
 	JEQ	noswitch
+	MOVL	m_g0(BP), SI
+	CMPL	DI, SI
+	JEQ	noswitch
 	CALL	gosave_systemstack_switch<>(SB)
 	get_tls(CX)
 	MOVL	SI, g(CX)
diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 2083ecb53e..a6b321aa42 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -667,22 +667,21 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	get_tls(CX)
-	MOVQ	g(CX), R8
-	CMPQ	R8, $0
-	JEQ	nosave
-	MOVQ	g_m(R8), R8
-	MOVQ	m_g0(R8), SI
 	MOVQ	g(CX), DI
-	CMPQ	SI, DI
+	CMPQ	DI, $0
 	JEQ	nosave
+	MOVQ	g_m(DI), R8
 	MOVQ	m_gsignal(R8), SI
-	CMPQ	SI, DI
+	CMPQ	DI, SI
+	JEQ	nosave
+	MOVQ	m_g0(R8), SI
+	CMPQ	DI, SI
 	JEQ	nosave
 
 	// Switch to system stack.
-	MOVQ	m_g0(R8), SI
 	CALL	gosave_systemstack_switch<>(SB)
 	MOVQ	SI, g(CX)
 	MOVQ	(g_sched+gobuf_sp)(SI), SP
diff --git a/src/runtime/asm_arm.s b/src/runtime/asm_arm.s
index a1164781d2..b47184e36b 100644
--- a/src/runtime/asm_arm.s
+++ b/src/runtime/asm_arm.s
@@ -556,7 +556,8 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-12
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	MOVW	g_m(g), R8
 	MOVW	m_gsignal(R8), R3
 	CMP	R3, g
diff --git a/src/runtime/asm_arm64.s b/src/runtime/asm_arm64.s
index e51ce2f831..8cbd17fa75 100644
--- a/src/runtime/asm_arm64.s
+++ b/src/runtime/asm_arm64.s
@@ -1027,7 +1027,8 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	MOVD	g_m(g), R8
 	MOVD	m_gsignal(R8), R3
 	CMP	R3, g
diff --git a/src/runtime/asm_mips64x.s b/src/runtime/asm_mips64x.s
index 940a38a0d6..e0e5cbb704 100644
--- a/src/runtime/asm_mips64x.s
+++ b/src/runtime/asm_mips64x.s
@@ -424,7 +424,8 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	MOVV	g_m(g), R5
 	MOVV	m_gsignal(R5), R6
 	BEQ	R6, g, g0
diff --git a/src/runtime/asm_mipsx.s b/src/runtime/asm_mipsx.s
index 87a1344e8f..1b550719d1 100644
--- a/src/runtime/asm_mipsx.s
+++ b/src/runtime/asm_mipsx.s
@@ -413,8 +413,11 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-12
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	MOVW	g_m(g), R5
+	MOVW	m_gsignal(R5), R6
+	BEQ	R6, g, g0
 	MOVW	m_g0(R5), R6
 	BEQ	R6, g, g0
 
diff --git a/src/runtime/asm_ppc64x.s b/src/runtime/asm_ppc64x.s
index 5dc96c5947..7270abbdee 100644
--- a/src/runtime/asm_ppc64x.s
+++ b/src/runtime/asm_ppc64x.s
@@ -541,9 +541,8 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
-	// Moreover, if it's called inside the signal handler, it must not switch
-	// to g0 as it can be in use by another syscall.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	MOVD	g_m(g), R8
 	MOVD	m_gsignal(R8), R6
 	CMP	R6, g
diff --git a/src/runtime/asm_riscv64.s b/src/runtime/asm_riscv64.s
index 9927a817f7..d7ab90d1ab 100644
--- a/src/runtime/asm_riscv64.s
+++ b/src/runtime/asm_riscv64.s
@@ -310,8 +310,11 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	MOV	g_m(g), X6
+	MOV	m_gsignal(X6), X7
+	BEQ	X7, g, g0
 	MOV	m_g0(X6), X7
 	BEQ	X7, g, g0
 
diff --git a/src/runtime/asm_s390x.s b/src/runtime/asm_s390x.s
index d4110d563f..5894fe5783 100644
--- a/src/runtime/asm_s390x.s
+++ b/src/runtime/asm_s390x.s
@@ -513,12 +513,15 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 
 	// Figure out if we need to switch to m->g0 stack.
 	// We get called to create new OS threads too, and those
-	// come in on the m->g0 stack already.
+	// come in on the m->g0 stack already. Or we might already
+	// be on the m->gsignal stack.
 	MOVD	g_m(g), R6
-	MOVD	m_g0(R6), R6
-	CMPBEQ	R6, g, g0
+	MOVD	m_gsignal(R6), R7
+	CMPBEQ	R7, g, g0
+	MOVD	m_g0(R6), R7
+	CMPBEQ	R7, g, g0
 	BL	gosave_systemstack_switch<>(SB)
-	MOVD	R6, g
+	MOVD	R7, g
 	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R15