runtime: unify C->Go ABI transitions

The previous CL introduced macros for transitions from the Windows ABI
to the Go ABI. This CL does the same for SysV and uses them in almost
all places where we transition from the C ABI to the Go ABI.

Compared to Windows, this transition is much simpler and I didn't find
any places that were getting it wrong. But this does let us unify a
lot of code nicely and introduces some degree of abstraction around
these ABI transitions.

Change-Id: Ib6bdecafce587ce18fca4c8300fcf401284a2bcd
Reviewed-on: https://go-review.googlesource.com/c/go/+/309930
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

2 files changed, 37 insertions, 25 deletions

diff --git a/src/runtime/cgo/abi_amd64.h b/src/runtime/cgo/abi_amd64.h
index 44cc0969da..9949435fe9 100644
--- a/src/runtime/cgo/abi_amd64.h
+++ b/src/runtime/cgo/abi_amd64.h
@@ -4,7 +4,9 @@
 
 // Macros for transitioning from the host ABI to Go ABI0.
 //
-// TODO(austin): Define these for ELF platforms as well.
+// These save the frame pointer, so in general, functions that use
+// these should have zero frame size to suppress the automatic frame
+// pointer, though it's harmless to not do this.
 
 #ifdef GOOS_windows
 
@@ -66,4 +68,32 @@
 	ADJSP	$-(REGS_HOST_TO_ABI0_STACK - 8)	\
 	POPFQ
 
+#else
+// SysV ABI
+
+#define REGS_HOST_TO_ABI0_STACK (6*8)
+
+// SysV MXCSR matches the Go ABI, so we don't have to set that,
+// and Go doesn't modify it, so we don't have to save it.
+// Both SysV and Go require DF to be cleared, so that's already clear.
+// The SysV and Go frame pointer conventions are compatible.
+#define PUSH_REGS_HOST_TO_ABI0()	\
+	ADJSP	$(REGS_HOST_TO_ABI0_STACK)	\
+	MOVQ	BP, (5*8)(SP)	\
+	LEAQ	(5*8)(SP), BP	\
+	MOVQ	BX, (0*8)(SP)	\
+	MOVQ	R12, (1*8)(SP)	\
+	MOVQ	R13, (2*8)(SP)	\
+	MOVQ	R14, (3*8)(SP)	\
+	MOVQ	R15, (4*8)(SP)
+
+#define POP_REGS_HOST_TO_ABI0()	\
+	MOVQ	(0*8)(SP), BX	\
+	MOVQ	(1*8)(SP), R12	\
+	MOVQ	(2*8)(SP), R13	\
+	MOVQ	(3*8)(SP), R14	\
+	MOVQ	(4*8)(SP), R15	\
+	MOVQ	(5*8)(SP), BP	\
+	ADJSP	$-(REGS_HOST_TO_ABI0_STACK)
+
 #endif
diff --git a/src/runtime/cgo/asm_amd64.s b/src/runtime/cgo/asm_amd64.s
index 447ddb118d..386299c548 100644
--- a/src/runtime/cgo/asm_amd64.s
+++ b/src/runtime/cgo/asm_amd64.s
@@ -10,43 +10,25 @@
 // Saves C callee-saved registers and calls cgocallback with three arguments.
 // fn is the PC of a func(a unsafe.Pointer) function.
 // This signature is known to SWIG, so we can't change it.
-#ifndef GOOS_windows
-TEXT crosscall2(SB),NOSPLIT,$0x50-0 /* keeps stack pointer 32-byte aligned */
-	MOVQ	BX, 0x18(SP)
-	MOVQ	R12, 0x28(SP)
-	MOVQ	R13, 0x30(SP)
-	MOVQ	R14, 0x38(SP)
-	MOVQ	R15, 0x40(SP)
+TEXT crosscall2(SB),NOSPLIT,$0-0
+	PUSH_REGS_HOST_TO_ABI0()
 
+	// Make room for arguments to cgocallback.
+	ADJSP	$0x18
+#ifndef GOOS_windows
 	MOVQ	DI, 0x0(SP)	/* fn */
 	MOVQ	SI, 0x8(SP)	/* arg */
 	// Skip n in DX.
 	MOVQ	CX, 0x10(SP)	/* ctxt */
-
-	CALL	runtime·cgocallback(SB)
-
-	MOVQ	0x18(SP), BX
-	MOVQ	0x28(SP), R12
-	MOVQ	0x30(SP), R13
-	MOVQ	0x38(SP), R14
-	MOVQ	0x40(SP), R15
-
-	RET
-
 #else
-TEXT crosscall2(SB),NOSPLIT,$0-0
-	PUSH_REGS_HOST_TO_ABI0()
-
-	// Make room for arguments to cgocallback.
-	ADJSP	$0x18
 	MOVQ	CX, 0x0(SP)	/* fn */
 	MOVQ	DX, 0x8(SP)	/* arg */
 	// Skip n in R8.
 	MOVQ	R9, 0x10(SP)	/* ctxt */
+#endif
 
 	CALL	runtime·cgocallback(SB)
 
 	ADJSP	$-0x18
 	POP_REGS_HOST_TO_ABI0()
 	RET
-#endif