all: add support for c-archive and c-shared on linux/riscv64

This provides the runtime glue (_rt0_riscv64_linux_lib) for c-archive and c-shared
support, along with enabling both of these buildmodes on linux/riscv64.

Both misc/cgo/testcarchive and misc/cgo/testcshared now pass on this platform.

Fixes #47100

Change-Id: I7ad75b23ae1d592dbac60d15bba557668287711f
Reviewed-on: https://go-review.googlesource.com/c/go/+/334872
Trust: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Mui <cherryyz@google.com>

misc/cgo/testcshared/testdata/libgo2/dup2.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux,!arm64 netbsd openbsd
+// +build darwin dragonfly freebsd linux,!arm64,!riscv64 netbsd openbsd
 
 package main
 

misc/cgo/testcshared/testdata/libgo2/dup3.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,arm64
+// +build linux,arm64 linux,riscv64
 
 package main
 

src/cmd/compile/internal/ssa/regalloc.go

@@ -635,6 +635,8 @@ func (s *regAllocState) init(f *Func) {
 			// nothing to do
 		case "ppc64le": // R2 already reserved.
 			// nothing to do
+		case "riscv64": // X3 (aka GP) and X4 (aka TP) already reserved.
+			// nothing to do
 		case "s390x":
 			s.allocatable &^= 1 << 11 // R11
 		default:

src/cmd/dist/test.go

@@ -1031,7 +1031,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		switch pair {
 		case "aix-ppc64",
 			"darwin-amd64", "darwin-arm64", "ios-arm64",
-			"linux-amd64", "linux-386", "linux-ppc64le", "linux-s390x",
+			"linux-amd64", "linux-386", "linux-ppc64le", "linux-riscv64", "linux-s390x",
 			"freebsd-amd64",
 			"windows-amd64", "windows-386":
 			return true
@@ -1039,7 +1039,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		return false
 	case "c-shared":
 		switch pair {
-		case "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le", "linux-s390x",
+		case "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le", "linux-riscv64", "linux-s390x",
 			"darwin-amd64", "darwin-arm64",
 			"freebsd-amd64",
 			"android-arm", "android-arm64", "android-386",

src/cmd/internal/sys/supported.go

@@ -105,7 +105,7 @@ func BuildModeSupported(compiler, buildmode, goos, goarch string) bool {
 
 	case "c-shared":
 		switch platform {
-		case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/ppc64le", "linux/s390x",
+		case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/ppc64le", "linux/riscv64", "linux/s390x",
 			"android/amd64", "android/arm", "android/arm64", "android/386",
 			"freebsd/amd64",
 			"darwin/amd64", "darwin/arm64",

src/cmd/link/internal/ld/config.go

@@ -74,7 +74,7 @@ func (mode *BuildMode) Set(s string) error {
 		*mode = BuildModeCArchive
 	case "c-shared":
 		switch buildcfg.GOARCH {
-		case "386", "amd64", "arm", "arm64", "ppc64le", "s390x":
+		case "386", "amd64", "arm", "arm64", "ppc64le", "riscv64", "s390x":
 		default:
 			return badmode()
 		}

src/runtime/rt0_linux_riscv64.s

@@ -9,6 +9,104 @@ TEXT _rt0_riscv64_linux(SB),NOSPLIT|NOFRAME,$0
 	ADD	$8, X2, A1	// argv
 	JMP	main(SB)
 
+// When building with -buildmode=c-shared, this symbol is called when the shared
+// library is loaded.
+TEXT _rt0_riscv64_linux_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)
+
+	// Initialize g as nil in case of using g later e.g. sigaction in cgo_sigaction.go
+	MOV	X0, g
+
+	MOV	A0, _rt0_riscv64_linux_lib_argc<>(SB)
+	MOV	A1, _rt0_riscv64_linux_lib_argv<>(SB)
+
+	// Synchronous initialization.
+	MOV	$runtime·libpreinit(SB), T0
+	JALR	RA, T0
+
+	// Create a new thread to do the runtime initialization and return.
+	MOV	_cgo_sys_thread_create(SB), T0
+	BEQZ	T0, nocgo
+	MOV	$_rt0_riscv64_linux_lib_go(SB), A0
+	MOV	$0, A1
+	JALR	RA, T0
+	JMP	restore
+
+nocgo:
+	MOV	$0x800000, A0                     // stacksize = 8192KB
+	MOV	$_rt0_riscv64_linux_lib_go(SB), A1
+	MOV	A0, 8(X2)
+	MOV	A1, 16(X2)
+	MOV	$runtime·newosproc0(SB), T0
+	JALR	RA, T0
+
+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
+
+	RET
+
+TEXT _rt0_riscv64_linux_lib_go(SB),NOSPLIT,$0
+	MOV	_rt0_riscv64_linux_lib_argc<>(SB), A0
+	MOV	_rt0_riscv64_linux_lib_argv<>(SB), A1
+	MOV	$runtime·rt0_go(SB), T0
+	JALR	ZERO, T0
+
+DATA _rt0_riscv64_linux_lib_argc<>(SB)/8, $0
+GLOBL _rt0_riscv64_linux_lib_argc<>(SB),NOPTR, $8
+DATA _rt0_riscv64_linux_lib_argv<>(SB)/8, $0
+GLOBL _rt0_riscv64_linux_lib_argv<>(SB),NOPTR, $8
+
+
 TEXT main(SB),NOSPLIT|NOFRAME,$0
 	MOV	$runtime·rt0_go(SB), T0
 	JALR	ZERO, T0