cmd/dist,cmd/go,runtime: add support for cgo on linux/riscv64
Fixes #36641
Change-Id: I51868d83ce341d78d33b221d184c5a5110c60d14
Reviewed-on: https://go-review.googlesource.com/c/go/+/263598
Trust: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/misc/cgo/test/testdata/issue9400/asm_riscv64.s b/misc/cgo/test/testdata/issue9400/asm_riscv64.s
new file mode 100644
index 0000000..20fcc00
--- /dev/null
+++ b/misc/cgo/test/testdata/issue9400/asm_riscv64.s
@@ -0,0 +1,31 @@
+// Copyright 2020 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.
+
+// +build riscv64
+// +build !gccgo
+
+#include "textflag.h"
+
+TEXT ·RewindAndSetgid(SB),NOSPLIT|NOFRAME,$0-0
+ // Rewind stack pointer so anything that happens on the stack
+ // will clobber the test pattern created by the caller
+ ADD $(1024*8), X2
+
+ // Ask signaller to setgid
+ MOV $1, X5
+ FENCE
+ MOVW X5, ·Baton(SB)
+ FENCE
+
+ // Wait for setgid completion
+loop:
+ FENCE
+ MOVW ·Baton(SB), X5
+ OR X6, X6, X6 // hint that we're in a spin loop
+ BNE ZERO, X5, loop
+ FENCE
+
+ // Restore stack
+ ADD $(-1024*8), X2
+ RET
diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index d822a83..20cb04d 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -1549,7 +1549,7 @@
"linux/mipsle": true,
"linux/mips64": true,
"linux/mips64le": true,
- "linux/riscv64": false, // Issue 36641
+ "linux/riscv64": true,
"linux/s390x": true,
"linux/sparc64": true,
"android/386": true,
diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index 9c25392..d12a52b 100644
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -953,7 +953,7 @@
// Internally linking cgo is incomplete on some architectures.
// https://golang.org/issue/10373
// https://golang.org/issue/14449
- if goarch == "mips64" || goarch == "mips64le" || goarch == "mips" || goarch == "mipsle" {
+ if goarch == "mips64" || goarch == "mips64le" || goarch == "mips" || goarch == "mipsle" || goarch == "riscv64" {
return false
}
if goos == "aix" {
@@ -1117,8 +1117,8 @@
"android-arm", "android-arm64",
"dragonfly-amd64",
"freebsd-386", "freebsd-amd64", "freebsd-arm",
- "linux-386", "linux-amd64", "linux-arm", "linux-ppc64le", "linux-s390x",
- "netbsd-386", "netbsd-amd64", "linux-arm64":
+ "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le", "linux-riscv64", "linux-s390x",
+ "netbsd-386", "netbsd-amd64":
cmd := t.addCmd(dt, "misc/cgo/test", t.goTest())
cmd.Env = append(os.Environ(), "GOFLAGS=-ldflags=-linkmode=external")
diff --git a/src/cmd/go/testdata/script/build_plugin_non_main.txt b/src/cmd/go/testdata/script/build_plugin_non_main.txt
index dba80c2..3c82dce 100644
--- a/src/cmd/go/testdata/script/build_plugin_non_main.txt
+++ b/src/cmd/go/testdata/script/build_plugin_non_main.txt
@@ -1,5 +1,6 @@
-# Plugins are only supported on linux,cgo and darwin,cgo.
+# Plugins are only supported on linux,cgo (!riscv64) and darwin,cgo.
[!linux] [!darwin] skip
+[linux] [riscv64] skip
[!cgo] skip
go build -n testdep
diff --git a/src/cmd/nm/nm_cgo_test.go b/src/cmd/nm/nm_cgo_test.go
index 9a257e0..e0414e6 100644
--- a/src/cmd/nm/nm_cgo_test.go
+++ b/src/cmd/nm/nm_cgo_test.go
@@ -24,7 +24,7 @@
}
case "linux":
switch runtime.GOARCH {
- case "arm64", "mips64", "mips64le", "mips", "mipsle", "ppc64", "ppc64le":
+ case "arm64", "mips64", "mips64le", "mips", "mipsle", "ppc64", "ppc64le", "riscv64":
return false
}
case "openbsd":
diff --git a/src/runtime/asm_riscv64.s b/src/runtime/asm_riscv64.s
index caaf42a..01b42dc 100644
--- a/src/runtime/asm_riscv64.s
+++ b/src/runtime/asm_riscv64.s
@@ -9,10 +9,9 @@
// func rt0_go()
TEXT runtime·rt0_go(SB),NOSPLIT,$0
// X2 = stack; A0 = argc; A1 = argv
-
ADD $-24, X2
- MOV A0, 8(X2) // argc
- MOV A1, 16(X2) // argv
+ MOV A0, 8(X2) // argc
+ MOV A1, 16(X2) // argv
// create istack out of the given (operating system) stack.
// _cgo_init may update stackguard.
@@ -28,10 +27,10 @@
MOV _cgo_init(SB), T0
BEQ T0, ZERO, nocgo
- MOV ZERO, A3 // arg 3: not used
- MOV ZERO, A2 // arg 2: not used
+ MOV ZERO, A3 // arg 3: not used
+ MOV ZERO, A2 // arg 2: not used
MOV $setg_gcc<>(SB), A1 // arg 1: setg
- MOV g, A0 // arg 0: G
+ MOV g, A0 // arg 0: G
JALR RA, T0
nocgo:
@@ -313,10 +312,62 @@
CALL runtime·badctxt(SB)
RET
+// Save state of caller into g->sched. Smashes X31.
+TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
+ MOV X1, (g_sched+gobuf_pc)(g)
+ MOV X2, (g_sched+gobuf_sp)(g)
+ MOV ZERO, (g_sched+gobuf_lr)(g)
+ MOV ZERO, (g_sched+gobuf_ret)(g)
+ // Assert ctxt is zero. See func save.
+ MOV (g_sched+gobuf_ctxt)(g), X31
+ BEQ ZERO, X31, 2(PC)
+ CALL runtime·badctxt(SB)
+ RET
+
// func asmcgocall(fn, arg unsafe.Pointer) int32
+// Call fn(arg) on the scheduler stack,
+// aligned appropriately for the gcc ABI.
+// See cgocall.go for more details.
TEXT ·asmcgocall(SB),NOSPLIT,$0-20
- // TODO(jsing): Add support for cgo - issue #36641.
- WORD $0 // crash
+ MOV fn+0(FP), X5
+ MOV arg+8(FP), X10
+
+ MOV X2, X8 // save original stack pointer
+ MOV g, X9
+
+ // 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.
+ MOV g_m(g), X6
+ MOV m_g0(X6), X7
+ BEQ X7, g, g0
+
+ CALL gosave<>(SB)
+ MOV X7, g
+ CALL runtime·save_g(SB)
+ MOV (g_sched+gobuf_sp)(g), X2
+
+ // Now on a scheduling stack (a pthread-created stack).
+g0:
+ // Save room for two of our pointers.
+ ADD $-16, X2
+ MOV X9, 0(X2) // save old g on stack
+ MOV (g_stack+stack_hi)(X9), X9
+ SUB X8, X9, X8
+ MOV X8, 8(X2) // save depth in old g stack (can't just save SP, as stack might be copied during a callback)
+
+ JALR RA, (X5)
+
+ // Restore g, stack pointer. X10 is return value.
+ MOV 0(X2), g
+ CALL runtime·save_g(SB)
+ MOV (g_stack+stack_hi)(g), X5
+ MOV 8(X2), X6
+ SUB X6, X5, X6
+ MOV X6, X2
+
+ MOVW X10, ret+16(FP)
+ RET
// func asminit()
TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0
@@ -444,6 +495,21 @@
CALLFN(·call536870912, 536870912)
CALLFN(·call1073741824, 1073741824)
+// Called from cgo wrappers, this function returns g->m->curg.stack.hi.
+// Must obey the gcc calling convention.
+TEXT _cgo_topofstack(SB),NOSPLIT,$8
+ // g (X27) and REG_TMP (X31) might be clobbered by load_g.
+ // X27 is callee-save in the gcc calling convention, so save it.
+ MOV g, savedX27-8(SP)
+
+ CALL runtime·load_g(SB)
+ MOV g_m(g), X5
+ MOV m_curg(X5), X5
+ MOV (g_stack+stack_hi)(X5), X10 // return value in X10
+
+ MOV savedX27-8(SP), g
+ RET
+
// func goexit(neverCallThisFunction)
// The top-most function running on a goroutine
// returns to goexit+PCQuantum.
@@ -453,11 +519,111 @@
// traceback from goexit1 must hit code range of goexit
MOV ZERO, ZERO // NOP
-// cgocallback(fn, frame unsafe.Pointer, ctxt uintptr)
+// func cgocallback(fn, frame unsafe.Pointer, ctxt uintptr)
// See cgocall.go for more details.
-TEXT ·cgocallback(SB),NOSPLIT,$0-24
- // TODO(jsing): Add support for cgo - issue #36641.
- WORD $0 // crash
+TEXT ·cgocallback(SB),NOSPLIT,$24-24
+ NO_LOCAL_POINTERS
+
+ // Load m and g from thread-local storage.
+ MOVBU runtime·iscgo(SB), X5
+ BEQ ZERO, X5, nocgo
+ CALL runtime·load_g(SB)
+nocgo:
+
+ // If g is nil, Go did not create the current thread.
+ // Call needm to obtain one for temporary use.
+ // In this case, we're running on the thread stack, so there's
+ // lots of space, but the linker doesn't know. Hide the call from
+ // the linker analysis by using an indirect call.
+ BEQ ZERO, g, needm
+
+ MOV g_m(g), X5
+ MOV X5, savedm-8(SP)
+ JMP havem
+
+needm:
+ MOV g, savedm-8(SP) // g is zero, so is m.
+ MOV $runtime·needm(SB), X6
+ JALR RA, X6
+
+ // Set m->sched.sp = SP, so that if a panic happens
+ // during the function we are about to execute, it will
+ // have a valid SP to run on the g0 stack.
+ // The next few lines (after the havem label)
+ // will save this SP onto the stack and then write
+ // the same SP back to m->sched.sp. That seems redundant,
+ // but if an unrecovered panic happens, unwindm will
+ // restore the g->sched.sp from the stack location
+ // and then systemstack will try to use it. If we don't set it here,
+ // that restored SP will be uninitialized (typically 0) and
+ // will not be usable.
+ MOV g_m(g), X5
+ MOV m_g0(X5), X6
+ MOV X2, (g_sched+gobuf_sp)(X6)
+
+havem:
+ // Now there's a valid m, and we're running on its m->g0.
+ // Save current m->g0->sched.sp on stack and then set it to SP.
+ // Save current sp in m->g0->sched.sp in preparation for
+ // switch back to m->curg stack.
+ // NOTE: unwindm knows that the saved g->sched.sp is at 8(X2) aka savedsp-24(SP).
+ MOV m_g0(X5), X6
+ MOV (g_sched+gobuf_sp)(X6), X7
+ MOV X7, savedsp-24(SP) // must match frame size
+ MOV X2, (g_sched+gobuf_sp)(X6)
+
+ // Switch to m->curg stack and call runtime.cgocallbackg.
+ // Because we are taking over the execution of m->curg
+ // but *not* resuming what had been running, we need to
+ // save that information (m->curg->sched) so we can restore it.
+ // We can restore m->curg->sched.sp easily, because calling
+ // runtime.cgocallbackg leaves SP unchanged upon return.
+ // To save m->curg->sched.pc, we push it onto the curg stack and
+ // open a frame the same size as cgocallback's g0 frame.
+ // Once we switch to the curg stack, the pushed PC will appear
+ // to be the return PC of cgocallback, so that the traceback
+ // will seamlessly trace back into the earlier calls.
+ MOV m_curg(X5), g
+ CALL runtime·save_g(SB)
+ MOV (g_sched+gobuf_sp)(g), X6 // prepare stack as X6
+ MOV (g_sched+gobuf_pc)(g), X7
+ MOV X7, -(24+8)(X6) // "saved LR"; must match frame size
+ // Gather our arguments into registers.
+ MOV fn+0(FP), X7
+ MOV frame+8(FP), X8
+ MOV ctxt+16(FP), X9
+ MOV $-(24+8)(X6), X2 // switch stack; must match frame size
+ MOV X7, 8(X2)
+ MOV X8, 16(X2)
+ MOV X9, 24(X2)
+ CALL runtime·cgocallbackg(SB)
+
+ // Restore g->sched (== m->curg->sched) from saved values.
+ MOV 0(X2), X7
+ MOV X7, (g_sched+gobuf_pc)(g)
+ MOV $(24+8)(X2), X6 // must match frame size
+ MOV X6, (g_sched+gobuf_sp)(g)
+
+ // Switch back to m->g0's stack and restore m->g0->sched.sp.
+ // (Unlike m->curg, the g0 goroutine never uses sched.pc,
+ // so we do not have to restore it.)
+ MOV g_m(g), X5
+ MOV m_g0(X5), g
+ CALL runtime·save_g(SB)
+ MOV (g_sched+gobuf_sp)(g), X2
+ MOV savedsp-24(SP), X6 // must match frame size
+ MOV X6, (g_sched+gobuf_sp)(g)
+
+ // If the m on entry was nil, we called needm above to borrow an m
+ // for the duration of the call. Since the call is over, return it with dropm.
+ MOV savedm-8(SP), X5
+ BNE ZERO, X5, droppedm
+ MOV $runtime·dropm(SB), X6
+ JALR RA, X6
+droppedm:
+
+ // Done!
+ RET
TEXT runtime·breakpoint(SB),NOSPLIT|NOFRAME,$0-0
EBREAK
diff --git a/src/runtime/cgo/asm_riscv64.s b/src/runtime/cgo/asm_riscv64.s
new file mode 100644
index 0000000..b4ddbb0
--- /dev/null
+++ b/src/runtime/cgo/asm_riscv64.s
@@ -0,0 +1,84 @@
+// Copyright 2020 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.
+
+// +build riscv64
+
+#include "textflag.h"
+
+// Called by C code generated by cmd/cgo.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
+TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
+ /*
+ * Push arguments for fn (X10, X11, X13), along with all callee-save
+ * registers. Note that at procedure entry the first argument is at
+ * 8(X2).
+ */
+ ADD $(-8*31), X2
+ 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)
+ MOV X3, (8*16)(X2)
+ MOV X4, (8*17)(X2)
+ MOV X1, (8*18)(X2)
+ MOVD F8, (8*19)(X2)
+ MOVD F9, (8*20)(X2)
+ MOVD F18, (8*21)(X2)
+ MOVD F19, (8*22)(X2)
+ MOVD F20, (8*23)(X2)
+ MOVD F21, (8*24)(X2)
+ MOVD F22, (8*25)(X2)
+ MOVD F23, (8*26)(X2)
+ MOVD F24, (8*27)(X2)
+ MOVD F25, (8*28)(X2)
+ MOVD F26, (8*29)(X2)
+ MOVD F27, (8*30)(X2)
+
+ // 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
+ MOV (8*16)(X2), X3
+ MOV (8*17)(X2), X4
+ MOV (8*18)(X2), X1
+ MOVD (8*19)(X2), F8
+ MOVD (8*20)(X2), F9
+ MOVD (8*21)(X2), F18
+ MOVD (8*22)(X2), F19
+ MOVD (8*23)(X2), F20
+ MOVD (8*24)(X2), F21
+ MOVD (8*25)(X2), F22
+ MOVD (8*26)(X2), F23
+ MOVD (8*27)(X2), F24
+ MOVD (8*28)(X2), F25
+ MOVD (8*29)(X2), F26
+ MOVD (8*30)(X2), F27
+ ADD $(8*31), X2
+
+ RET
diff --git a/src/runtime/cgo/gcc_linux_riscv64.c b/src/runtime/cgo/gcc_linux_riscv64.c
new file mode 100644
index 0000000..22b76c2
--- /dev/null
+++ b/src/runtime/cgo/gcc_linux_riscv64.c
@@ -0,0 +1,74 @@
+// Copyright 2020 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.
+
+#include <pthread.h>
+#include <string.h>
+#include <signal.h>
+#include "libcgo.h"
+#include "libcgo_unix.h"
+
+static void *threadentry(void*);
+
+void (*x_cgo_inittls)(void **tlsg, void **tlsbase);
+static void (*setg_gcc)(void*);
+
+void
+_cgo_sys_thread_start(ThreadStart *ts)
+{
+ pthread_attr_t attr;
+ sigset_t ign, oset;
+ pthread_t p;
+ size_t size;
+ int err;
+
+ sigfillset(&ign);
+ pthread_sigmask(SIG_SETMASK, &ign, &oset);
+
+ // Not sure why the memset is necessary here,
+ // but without it, we get a bogus stack size
+ // out of pthread_attr_getstacksize. C'est la Linux.
+ memset(&attr, 0, sizeof attr);
+ pthread_attr_init(&attr);
+ size = 0;
+ pthread_attr_getstacksize(&attr, &size);
+ // Leave stacklo=0 and set stackhi=size; mstart will do the rest.
+ ts->g->stackhi = size;
+ err = _cgo_try_pthread_create(&p, &attr, threadentry, ts);
+
+ pthread_sigmask(SIG_SETMASK, &oset, nil);
+
+ if (err != 0) {
+ fatalf("pthread_create failed: %s", strerror(err));
+ }
+}
+
+extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
+static void*
+threadentry(void *v)
+{
+ ThreadStart ts;
+
+ ts = *(ThreadStart*)v;
+ free(v);
+
+ crosscall1(ts.fn, setg_gcc, (void*)ts.g);
+ return nil;
+}
+
+void
+x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
+{
+ pthread_attr_t attr;
+ size_t size;
+
+ setg_gcc = setg;
+ pthread_attr_init(&attr);
+ pthread_attr_getstacksize(&attr, &size);
+ g->stacklo = (uintptr)&attr - size + 4096;
+ pthread_attr_destroy(&attr);
+
+ if (x_cgo_inittls) {
+ x_cgo_inittls(tlsg, tlsbase);
+ }
+}
diff --git a/src/runtime/cgo/gcc_riscv64.S b/src/runtime/cgo/gcc_riscv64.S
new file mode 100644
index 0000000..f429dc6
--- /dev/null
+++ b/src/runtime/cgo/gcc_riscv64.S
@@ -0,0 +1,80 @@
+// Copyright 2020 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.
+
+/*
+ * void crosscall1(void (*fn)(void), void (*setg_gcc)(void *g), void *g)
+ *
+ * Calling into the gc tool chain, where all registers are caller save.
+ * Called from standard RISCV ELF psABI, where x8-x9, x18-x27, f8-f9 and
+ * f18-f27 are callee-save, so they must be saved explicitly, along with
+ * x1 (LR).
+ */
+.globl crosscall1
+crosscall1:
+ sd x1, -200(sp)
+ addi sp, sp, -200
+ sd x8, 8(sp)
+ sd x9, 16(sp)
+ sd x18, 24(sp)
+ sd x19, 32(sp)
+ sd x20, 40(sp)
+ sd x21, 48(sp)
+ sd x22, 56(sp)
+ sd x23, 64(sp)
+ sd x24, 72(sp)
+ sd x25, 80(sp)
+ sd x26, 88(sp)
+ sd x27, 96(sp)
+ fsd f8, 104(sp)
+ fsd f9, 112(sp)
+ fsd f18, 120(sp)
+ fsd f19, 128(sp)
+ fsd f20, 136(sp)
+ fsd f21, 144(sp)
+ fsd f22, 152(sp)
+ fsd f23, 160(sp)
+ fsd f24, 168(sp)
+ fsd f25, 176(sp)
+ fsd f26, 184(sp)
+ fsd f27, 192(sp)
+
+ // a0 = *fn, a1 = *setg_gcc, a2 = *g
+ mv s1, a0
+ mv s0, a1
+ mv a0, a2
+ jalr ra, s0 // call setg_gcc (clobbers x30 aka g)
+ jalr ra, s1 // call fn
+
+ ld x1, 0(sp)
+ ld x8, 8(sp)
+ ld x9, 16(sp)
+ ld x18, 24(sp)
+ ld x19, 32(sp)
+ ld x20, 40(sp)
+ ld x21, 48(sp)
+ ld x22, 56(sp)
+ ld x23, 64(sp)
+ ld x24, 72(sp)
+ ld x25, 80(sp)
+ ld x26, 88(sp)
+ ld x27, 96(sp)
+ fld f8, 104(sp)
+ fld f9, 112(sp)
+ fld f18, 120(sp)
+ fld f19, 128(sp)
+ fld f20, 136(sp)
+ fld f21, 144(sp)
+ fld f22, 152(sp)
+ fld f23, 160(sp)
+ fld f24, 168(sp)
+ fld f25, 176(sp)
+ fld f26, 184(sp)
+ fld f27, 192(sp)
+ addi sp, sp, 200
+
+ jr ra
+
+#ifdef __ELF__
+.section .note.GNU-stack,"",%progbits
+#endif
diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go
index 9bca279..20cacd60 100644
--- a/src/runtime/cgocall.go
+++ b/src/runtime/cgocall.go
@@ -309,7 +309,7 @@
switch GOARCH {
default:
throw("unwindm not implemented")
- case "386", "amd64", "arm", "ppc64", "ppc64le", "mips64", "mips64le", "s390x", "mips", "mipsle":
+ case "386", "amd64", "arm", "ppc64", "ppc64le", "mips64", "mips64le", "s390x", "mips", "mipsle", "riscv64":
sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + sys.MinFrameSize))
case "arm64":
sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + 16))
diff --git a/src/runtime/tls_riscv64.s b/src/runtime/tls_riscv64.s
index 8386980..22b550b 100644
--- a/src/runtime/tls_riscv64.s
+++ b/src/runtime/tls_riscv64.s
@@ -9,10 +9,22 @@
// If !iscgo, this is a no-op.
//
-// NOTE: mcall() assumes this clobbers only R23 (REGTMP).
-// FIXME: cgo
+// NOTE: mcall() assumes this clobbers only X31 (REG_TMP).
TEXT runtime·save_g(SB),NOSPLIT|NOFRAME,$0-0
+ MOVB runtime·iscgo(SB), X31
+ BEQ X0, X31, nocgo
+
+ MOV runtime·tls_g(SB), X31
+ ADD X4, X31 // add offset to thread pointer (X4)
+ MOV g, (X31)
+
+nocgo:
RET
TEXT runtime·load_g(SB),NOSPLIT|NOFRAME,$0-0
+ MOV runtime·tls_g(SB), X31
+ ADD X4, X31 // add offset to thread pointer (X4)
+ MOV (X31), g
RET
+
+GLOBL runtime·tls_g(SB), TLSBSS, $8
