runtime/cgo: add abi_riscv64.h for callee-saved register macros

Add abi_riscv64.h with SAVE_GPR/SAVE_FPR macros for saving and
restoring the RISC-V callee-saved registers, following the pattern
established by the other abi_*.h headers.

Refactor asm_riscv64.s (cgo crosscall2), asm_riscv64.s (runtime
_rt0_riscv64_lib), and race_riscv64.s (racecallbackthunk) to use
the new macros, replacing inline register save/restore sequences.

Change-Id: I83cef17a35c57fc8b5e045e7181460283ae5b423
Reviewed-on: https://go-review.googlesource.com/c/go/+/749900
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>

4 files changed, 89 insertions, 144 deletions

diff --git a/src/runtime/asm_riscv64.s b/src/runtime/asm_riscv64.s
index d74f388752..b59998960d 100644
--- a/src/runtime/asm_riscv64.s
+++ b/src/runtime/asm_riscv64.s
@@ -5,6 +5,7 @@
 #include "go_asm.h"
 #include "funcdata.h"
 #include "textflag.h"
+#include "cgo/abi_riscv64.h"
 
 
 // When building with -buildmode=c-shared, this symbol is called when the shared
@@ -12,30 +13,8 @@
 TEXT _rt0_riscv64_lib(SB),NOSPLIT,$224
 	// Preserve callee-save registers, along with X1 (LR).
 	MOV	X1, (8*3)(X2)
-	MOV	X8, (8*4)(X2)
-	MOV	X9, (8*5)(X2)
-	MOV	X18, (8*6)(X2)
-	MOV	X19, (8*7)(X2)
-	MOV	X20, (8*8)(X2)
-	MOV	X21, (8*9)(X2)
-	MOV	X22, (8*10)(X2)
-	MOV	X23, (8*11)(X2)
-	MOV	X24, (8*12)(X2)
-	MOV	X25, (8*13)(X2)
-	MOV	X26, (8*14)(X2)
-	MOV	g, (8*15)(X2)
-	MOVD	F8, (8*16)(X2)
-	MOVD	F9, (8*17)(X2)
-	MOVD	F18, (8*18)(X2)
-	MOVD	F19, (8*19)(X2)
-	MOVD	F20, (8*20)(X2)
-	MOVD	F21, (8*21)(X2)
-	MOVD	F22, (8*22)(X2)
-	MOVD	F23, (8*23)(X2)
-	MOVD	F24, (8*24)(X2)
-	MOVD	F25, (8*25)(X2)
-	MOVD	F26, (8*26)(X2)
-	MOVD	F27, (8*27)(X2)
+	SAVE_GPR((8*4))
+	SAVE_FPR((8*16))
 
 	// Initialize g as nil in case of using g later e.g. sigaction in cgo_sigaction.go
 	MOV	X0, g
@@ -66,30 +45,8 @@ nocgo:
 restore:
 	// Restore callee-save registers, along with X1 (LR).
 	MOV	(8*3)(X2), X1
-	MOV	(8*4)(X2), X8
-	MOV	(8*5)(X2), X9
-	MOV	(8*6)(X2), X18
-	MOV	(8*7)(X2), X19
-	MOV	(8*8)(X2), X20
-	MOV	(8*9)(X2), X21
-	MOV	(8*10)(X2), X22
-	MOV	(8*11)(X2), X23
-	MOV	(8*12)(X2), X24
-	MOV	(8*13)(X2), X25
-	MOV	(8*14)(X2), X26
-	MOV	(8*15)(X2), g
-	MOVD	(8*16)(X2), F8
-	MOVD	(8*17)(X2), F9
-	MOVD	(8*18)(X2), F18
-	MOVD	(8*19)(X2), F19
-	MOVD	(8*20)(X2), F20
-	MOVD	(8*21)(X2), F21
-	MOVD	(8*22)(X2), F22
-	MOVD	(8*23)(X2), F23
-	MOVD	(8*24)(X2), F24
-	MOVD	(8*25)(X2), F25
-	MOVD	(8*26)(X2), F26
-	MOVD	(8*27)(X2), F27
+	RESTORE_GPR((8*4))
+	RESTORE_FPR((8*16))
 
 	RET
 
diff --git a/src/runtime/cgo/abi_riscv64.h b/src/runtime/cgo/abi_riscv64.h
new file mode 100644
index 0000000000..b9322e0c53
--- /dev/null
+++ b/src/runtime/cgo/abi_riscv64.h
@@ -0,0 +1,72 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Macros for transitioning from the host ABI to Go ABI0.
+//
+// These macros save and restore the callee-saved registers
+// from the stack, but they don't adjust stack pointer, so
+// the user should prepare stack space in advance.
+// SAVE_GPR(offset) saves X8, X9, X18-X27 to the stack space
+// of ((offset)+0*8)(X2) ~ ((offset)+11*8)(X2).
+//
+// SAVE_FPR(offset) saves F8, F9, F18-F27 to the stack space
+// of ((offset)+0*8)(X2) ~ ((offset)+11*8)(X2).
+//
+// Note: g is X27
+
+#define SAVE_GPR(offset) \
+	MOV X8, ((offset)+0*8)(X2)   \
+	MOV X9, ((offset)+1*8)(X2)   \
+	MOV X18, ((offset)+2*8)(X2)  \
+	MOV X19, ((offset)+3*8)(X2)  \
+	MOV X20, ((offset)+4*8)(X2)  \
+	MOV X21, ((offset)+5*8)(X2)  \
+	MOV X22, ((offset)+6*8)(X2)  \
+	MOV X23, ((offset)+7*8)(X2)  \
+	MOV X24, ((offset)+8*8)(X2)  \
+	MOV X25, ((offset)+9*8)(X2)  \
+	MOV X26, ((offset)+10*8)(X2) \
+	MOV g, ((offset)+11*8)(X2)
+
+#define RESTORE_GPR(offset) \
+	MOV ((offset)+0*8)(X2), X8   \
+	MOV ((offset)+1*8)(X2), X9   \
+	MOV ((offset)+2*8)(X2), X18  \
+	MOV ((offset)+3*8)(X2), X19  \
+	MOV ((offset)+4*8)(X2), X20  \
+	MOV ((offset)+5*8)(X2), X21  \
+	MOV ((offset)+6*8)(X2), X22  \
+	MOV ((offset)+7*8)(X2), X23  \
+	MOV ((offset)+8*8)(X2), X24  \
+	MOV ((offset)+9*8)(X2), X25  \
+	MOV ((offset)+10*8)(X2), X26 \
+	MOV ((offset)+11*8)(X2), g
+
+#define SAVE_FPR(offset) \
+	MOVD F8, ((offset)+0*8)(X2)   \
+	MOVD F9, ((offset)+1*8)(X2)   \
+	MOVD F18, ((offset)+2*8)(X2)  \
+	MOVD F19, ((offset)+3*8)(X2)  \
+	MOVD F20, ((offset)+4*8)(X2)  \
+	MOVD F21, ((offset)+5*8)(X2)  \
+	MOVD F22, ((offset)+6*8)(X2)  \
+	MOVD F23, ((offset)+7*8)(X2)  \
+	MOVD F24, ((offset)+8*8)(X2)  \
+	MOVD F25, ((offset)+9*8)(X2)  \
+	MOVD F26, ((offset)+10*8)(X2) \
+	MOVD F27, ((offset)+11*8)(X2)
+
+#define RESTORE_FPR(offset) \
+	MOVD ((offset)+0*8)(X2), F8   \
+	MOVD ((offset)+1*8)(X2), F9   \
+	MOVD ((offset)+2*8)(X2), F18  \
+	MOVD ((offset)+3*8)(X2), F19  \
+	MOVD ((offset)+4*8)(X2), F20  \
+	MOVD ((offset)+5*8)(X2), F21  \
+	MOVD ((offset)+6*8)(X2), F22  \
+	MOVD ((offset)+7*8)(X2), F23  \
+	MOVD ((offset)+8*8)(X2), F24  \
+	MOVD ((offset)+9*8)(X2), F25  \
+	MOVD ((offset)+10*8)(X2), F26 \
+	MOVD ((offset)+11*8)(X2), F27
diff --git a/src/runtime/cgo/asm_riscv64.s b/src/runtime/cgo/asm_riscv64.s
index d75a543842..d8be554977 100644
--- a/src/runtime/cgo/asm_riscv64.s
+++ b/src/runtime/cgo/asm_riscv64.s
@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 #include "textflag.h"
+#include "abi_riscv64.h"
 
 // Set the x_crosscall2_ptr C function pointer variable point to crosscall2.
 // It's such a pointer chain: _crosscall2_ptr -> x_crosscall2_ptr -> crosscall2
@@ -31,61 +32,19 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	MOV	X10, (8*1)(X2) // fn unsafe.Pointer
 	MOV	X11, (8*2)(X2) // a unsafe.Pointer
 	MOV	X13, (8*3)(X2) // ctxt uintptr
-	MOV	X8, (8*4)(X2)
-	MOV	X9, (8*5)(X2)
-	MOV	X18, (8*6)(X2)
-	MOV	X19, (8*7)(X2)
-	MOV	X20, (8*8)(X2)
-	MOV	X21, (8*9)(X2)
-	MOV	X22, (8*10)(X2)
-	MOV	X23, (8*11)(X2)
-	MOV	X24, (8*12)(X2)
-	MOV	X25, (8*13)(X2)
-	MOV	X26, (8*14)(X2)
-	MOV	g, (8*15)(X2)
+
+	SAVE_GPR((8*4))
 	MOV	X1, (8*16)(X2)
-	MOVD	F8, (8*17)(X2)
-	MOVD	F9, (8*18)(X2)
-	MOVD	F18, (8*19)(X2)
-	MOVD	F19, (8*20)(X2)
-	MOVD	F20, (8*21)(X2)
-	MOVD	F21, (8*22)(X2)
-	MOVD	F22, (8*23)(X2)
-	MOVD	F23, (8*24)(X2)
-	MOVD	F24, (8*25)(X2)
-	MOVD	F25, (8*26)(X2)
-	MOVD	F26, (8*27)(X2)
-	MOVD	F27, (8*28)(X2)
+	SAVE_FPR((8*17))
 
 	// Initialize Go ABI environment
 	CALL	runtime·load_g(SB)
 	CALL	runtime·cgocallback(SB)
 
-	MOV	(8*4)(X2), X8
-	MOV	(8*5)(X2), X9
-	MOV	(8*6)(X2), X18
-	MOV	(8*7)(X2), X19
-	MOV	(8*8)(X2), X20
-	MOV	(8*9)(X2), X21
-	MOV	(8*10)(X2), X22
-	MOV	(8*11)(X2), X23
-	MOV	(8*12)(X2), X24
-	MOV	(8*13)(X2), X25
-	MOV	(8*14)(X2), X26
-	MOV	(8*15)(X2), g
+	RESTORE_GPR((8*4))
 	MOV	(8*16)(X2), X1
-	MOVD	(8*17)(X2), F8
-	MOVD	(8*18)(X2), F9
-	MOVD	(8*19)(X2), F18
-	MOVD	(8*20)(X2), F19
-	MOVD	(8*21)(X2), F20
-	MOVD	(8*22)(X2), F21
-	MOVD	(8*23)(X2), F22
-	MOVD	(8*24)(X2), F23
-	MOVD	(8*25)(X2), F24
-	MOVD	(8*26)(X2), F25
-	MOVD	(8*27)(X2), F26
-	MOVD	(8*28)(X2), F27
+	RESTORE_FPR((8*17))
+
 	ADD	$(8*29), X2
 
 	RET
diff --git a/src/runtime/race_riscv64.s b/src/runtime/race_riscv64.s
index a455c9e496..26ea43420c 100644
--- a/src/runtime/race_riscv64.s
+++ b/src/runtime/race_riscv64.s
@@ -7,6 +7,7 @@
 #include "go_asm.h"
 #include "funcdata.h"
 #include "textflag.h"
+#include "cgo/abi_riscv64.h"
 
 // The following thunks allow calling the gcc-compiled race runtime directly
 // from Go code without going all the way through cgo.
@@ -473,30 +474,8 @@ rest:
 	// 8(X2) and 16(X2) are for args passed to racecallback
 	SUB	$(27*8), X2
 	MOV	X1, (0*8)(X2)
-	MOV	X8, (3*8)(X2)
-	MOV	X9, (4*8)(X2)
-	MOV	X18, (5*8)(X2)
-	MOV	X19, (6*8)(X2)
-	MOV	X20, (7*8)(X2)
-	MOV	X21, (8*8)(X2)
-	MOV	X22, (9*8)(X2)
-	MOV	X23, (10*8)(X2)
-	MOV	X24, (11*8)(X2)
-	MOV	X25, (12*8)(X2)
-	MOV	X26, (13*8)(X2)
-	MOV	g, (14*8)(X2)
-	MOVD	F8, (15*8)(X2)
-	MOVD	F9, (16*8)(X2)
-	MOVD	F18, (17*8)(X2)
-	MOVD	F19, (18*8)(X2)
-	MOVD	F20, (19*8)(X2)
-	MOVD	F21, (20*8)(X2)
-	MOVD	F22, (21*8)(X2)
-	MOVD	F23, (22*8)(X2)
-	MOVD	F24, (23*8)(X2)
-	MOVD	F25, (24*8)(X2)
-	MOVD	F26, (25*8)(X2)
-	MOVD	F27, (26*8)(X2)
+	SAVE_GPR((3*8))
+	SAVE_FPR((15*8))
 
 	// Set g = g0.
 	CALL	runtime·load_g(SB)
@@ -515,30 +494,8 @@ rest:
 ret:
 	// Restore callee-save registers.
 	MOV	(0*8)(X2), X1
-	MOV	(3*8)(X2), X8
-	MOV	(4*8)(X2), X9
-	MOV	(5*8)(X2), X18
-	MOV	(6*8)(X2), X19
-	MOV	(7*8)(X2), X20
-	MOV	(8*8)(X2), X21
-	MOV	(9*8)(X2), X22
-	MOV	(10*8)(X2), X23
-	MOV	(11*8)(X2), X24
-	MOV	(12*8)(X2), X25
-	MOV	(13*8)(X2), X26
-	MOV	(14*8)(X2), g
-	MOVD	(15*8)(X2), F8
-	MOVD	(16*8)(X2), F9
-	MOVD	(17*8)(X2), F18
-	MOVD	(18*8)(X2), F19
-	MOVD	(19*8)(X2), F20
-	MOVD	(20*8)(X2), F21
-	MOVD	(21*8)(X2), F22
-	MOVD	(22*8)(X2), F23
-	MOVD	(23*8)(X2), F24
-	MOVD	(24*8)(X2), F25
-	MOVD	(25*8)(X2), F26
-	MOVD	(26*8)(X2), F27
+	RESTORE_GPR((3*8))
+	RESTORE_FPR((15*8))
 
 	ADD	$(27*8), X2
 	JMP	(X1)