runtime: remove NOFRAME from asmcgocall, systemstack and mcall

This CL removes the NOFRAME flag from runtime.asmcgocall,
runtime.systemstack and runtime.mcall so the compiler can place
the frame pointer on the stack.

This will help unwinding cgo stack frames, and might be all what's
needed for tools that only use the frame pointer to unwind the stack.
That's not the case for gdb, which uses DWARF CFI, and windbg,
which uses SEH. Yet, having the frame pointer correctly set lays
the foundation for supporting cgo unwinding with DWARF CFI and SEH.

Updates #58378

Change-Id: I7655363b3fb619acccd9d5a7f0e3d3dec953cd52
Reviewed-on: https://go-review.googlesource.com/c/go/+/472195
Run-TryBot: Quim Muntal <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: qmuntal

src/runtime/asm_amd64.s

@@ -425,11 +425,14 @@ TEXT gogo<>(SB), NOSPLIT, $0
 // Switch to m->g0's stack, call fn(g).
 // Fn must never return. It should gogo(&g->sched)
 // to keep running g.
-TEXT runtime·mcall<ABIInternal>(SB), NOSPLIT|NOFRAME, $0-8
+TEXT runtime·mcall<ABIInternal>(SB), NOSPLIT, $0-8
 	MOVQ	AX, DX	// DX = fn
 
-	// save state in g->sched
-	MOVQ	0(SP), BX	// caller's PC
+	// Save state in g->sched.
+	// The original frame pointer is stored in BP,
+	// which is useful for stack unwinding.
+	MOVQ	SP, BX	// hide (SP) reads from vet
+	MOVQ	8(BX), BX	// caller's PC
 	MOVQ	BX, (g_sched+gobuf_pc)(R14)
 	LEAQ	fn+0(FP), BX	// caller's SP
 	MOVQ	BX, (g_sched+gobuf_sp)(R14)
@@ -459,11 +462,17 @@ goodm:
 // lives at the bottom of the G stack from the one that lives
 // at the top of the system stack because the one at the top of
 // the system stack terminates the stack walk (see topofstack()).
+// The frame layout needs to match systemstack
+// so that it can pretend to be systemstack_switch.
 TEXT runtime·systemstack_switch(SB), NOSPLIT, $0-0
+	UNDEF
+	// Make sure this function is not leaf,
+	// so the frame is saved.
+	CALL	runtime·abort(SB)
 	RET
 
 // func systemstack(fn func())
-TEXT runtime·systemstack(SB), NOSPLIT|NOFRAME, $0-8
+TEXT runtime·systemstack(SB), NOSPLIT, $0-8
 	MOVQ	fn+0(FP), DI	// DI = fn
 	get_tls(CX)
 	MOVQ	g(CX), AX	// AX = g
@@ -479,16 +488,17 @@ TEXT runtime·systemstack(SB), NOSPLIT|NOFRAME, $0-8
 	CMPQ	AX, m_curg(BX)
 	JNE	bad
 
-	// switch stacks
-	// save our state in g->sched. Pretend to
+	// Switch stacks.
+	// The original frame pointer is stored in BP,
+	// which is useful for stack unwinding.
+	// Save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
 	CALL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVQ	DX, g(CX)
 	MOVQ	DX, R14 // set the g register
-	MOVQ	(g_sched+gobuf_sp)(DX), BX
-	MOVQ	BX, SP
+	MOVQ	(g_sched+gobuf_sp)(DX), SP
 
 	// call target function
 	MOVQ	DI, DX
@@ -502,7 +512,9 @@ TEXT runtime·systemstack(SB), NOSPLIT|NOFRAME, $0-8
 	MOVQ	m_curg(BX), AX
 	MOVQ	AX, g(CX)
 	MOVQ	(g_sched+gobuf_sp)(AX), SP
+	MOVQ	(g_sched+gobuf_bp)(AX), BP
 	MOVQ	$0, (g_sched+gobuf_sp)(AX)
+	MOVQ	$0, (g_sched+gobuf_bp)(AX)
 	RET
 
 noswitch:
@@ -511,6 +523,9 @@ noswitch:
 	// at an intermediate systemstack.
 	MOVQ	DI, DX
 	MOVQ	0(DI), DI
+	// The function epilogue is not called on a tail call.
+	// Pop BP from the stack to simulate it.
+	POPQ	BP
 	JMP	DI
 
 bad:
@@ -571,6 +586,7 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
 	MOVQ	m_g0(BX), BX
 	MOVQ	BX, g(CX)
 	MOVQ	(g_sched+gobuf_sp)(BX), SP
+	MOVQ	(g_sched+gobuf_bp)(BX), BP
 	CALL	runtime·newstack(SB)
 	CALL	runtime·abort(SB)	// crash if newstack returns
 	RET
@@ -769,11 +785,15 @@ TEXT ·publicationBarrier<ABIInternal>(SB),NOSPLIT,$0-0
 
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
-// Must only be called from functions with no locals ($0)
-// or else unwinding from systemstack_switch is incorrect.
+// Must only be called from functions with frame pointer
+// and without locals ($0) or else unwinding from
+// systemstack_switch is incorrect.
 // Smashes R9.
 TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
-	MOVQ	$runtime·systemstack_switch(SB), R9
+	// Take systemstack_switch PC and add 8 bytes to skip
+	// the prologue. The final location does not matter
+	// as long as we are between the prologue and the epilogue.
+	MOVQ	$runtime·systemstack_switch+8(SB), R9
 	MOVQ	R9, (g_sched+gobuf_pc)(R14)
 	LEAQ	8(SP), R9
 	MOVQ	R9, (g_sched+gobuf_sp)(R14)
@@ -789,11 +809,10 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
 // func asmcgocall_no_g(fn, arg unsafe.Pointer)
 // Call fn(arg) aligned appropriately for the gcc ABI.
 // Called on a system stack, and there may be no g yet (during needm).
-TEXT ·asmcgocall_no_g(SB),NOSPLIT|NOFRAME,$0-16
+TEXT ·asmcgocall_no_g(SB),NOSPLIT,$32-16
 	MOVQ	fn+0(FP), AX
 	MOVQ	arg+8(FP), BX
 	MOVQ	SP, DX
-	SUBQ	$32, SP
 	ANDQ	$~15, SP	// alignment
 	MOVQ	DX, 8(SP)
 	MOVQ	BX, DI		// DI = first argument in AMD64 ABI
@@ -807,7 +826,7 @@ TEXT ·asmcgocall_no_g(SB),NOSPLIT|NOFRAME,$0-16
 // Call fn(arg) on the scheduler stack,
 // aligned appropriately for the gcc ABI.
 // See cgocall.go for more details.
-TEXT ·asmcgocall(SB),NOSPLIT|NOFRAME,$0-20
+TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 	MOVQ	fn+0(FP), AX
 	MOVQ	arg+8(FP), BX
 
@@ -830,6 +849,8 @@ TEXT ·asmcgocall(SB),NOSPLIT|NOFRAME,$0-20
 	JEQ	nosave
 
 	// Switch to system stack.
+	// The original frame pointer is stored in BP,
+	// which is useful for stack unwinding.
 	CALL	gosave_systemstack_switch<>(SB)
 	MOVQ	SI, g(CX)
 	MOVQ	(g_sched+gobuf_sp)(SI), SP