cmd,runtime: enable race detector on arm64

Changes include: 1. enable compiler option -race for arm64 2. add runtime/race_arm64.s to manage the calls from Go to the compiler-rt runtime 3. change racewalk.go to call racefuncenterfp instead of racefuncenter on arm64 to allow the caller pc to be obtained in the asm code before calling the tsan version 4. race_linux_arm64.syso comes from compiler-rt which just supports 48bit VA, compiler-rt is fetched from master branch which latest commit is 3aa2b775d08f903f804246af10b Fixes #25682 Change-Id: I04364c580b8157fd117deecae74a4656ba16e005 Reviewed-on: https://go-review.googlesource.com/c/138675 Run-TryBot: Cherry Zhang <cherryyz@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Cherry Zhang <cherryyz@google.com>
2024-11-23 09:30:03 -07:00 · 2018-06-20 09:09:03 +00:00 · 2018-06-20 09:09:03 +00:00 · 978cfa8e46
commit 978cfa8e46
parent e787b13328
10 changed files with 457 additions and 10 deletions
--- a/src/cmd/compile/internal/gc/racewalk.go
+++ b/src/cmd/compile/internal/gc/racewalk.go
@ -71,14 +71,14 @@ func instrument(fn *Node) {
 		lno := lineno
 		lineno = src.NoXPos

-		if thearch.LinkArch.Arch == sys.ArchPPC64LE {
+		if thearch.LinkArch.Arch.Family != sys.AMD64 {
 			fn.Func.Enter.Prepend(mkcall("racefuncenterfp", nil, nil))
 			fn.Func.Exit.Append(mkcall("racefuncexit", nil, nil))
 		} else {

 			// nodpc is the PC of the caller as extracted by
 			// getcallerpc. We use -widthptr(FP) for x86.
-			// BUG: This only works for amd64. This will not
+			// This only works for amd64. This will not
 			// work on arm or others that might support
 			// race in the future.
 			nodpc := nodfp.copy()
--- a/src/cmd/go/internal/work/init.go
+++ b/src/cmd/go/internal/work/init.go
@ -49,7 +49,7 @@ func instrumentInit() {
 	}
 	if cfg.BuildRace {
 		if !sys.RaceDetectorSupported(cfg.Goos, cfg.Goarch) {
-			fmt.Fprintf(os.Stderr, "go %s: -race is only supported on linux/amd64, linux/ppc64le, freebsd/amd64, netbsd/amd64, darwin/amd64 and windows/amd64\n", flag.Args()[0])
+			fmt.Fprintf(os.Stderr, "go %s: -race is only supported on linux/amd64, linux/ppc64le, linux/arm64, freebsd/amd64, netbsd/amd64, darwin/amd64 and windows/amd64\n", flag.Args()[0])
 			os.Exit(2)
 		}
 	}
--- a/src/cmd/internal/sys/supported.go
+++ b/src/cmd/internal/sys/supported.go
@ -9,7 +9,7 @@ package sys
 func RaceDetectorSupported(goos, goarch string) bool {
 	switch goos {
 	case "linux":
-		return goarch == "amd64" || goarch == "ppc64le"
+		return goarch == "amd64" || goarch == "ppc64le" || goarch == "arm64"
 	case "darwin", "freebsd", "netbsd", "windows":
 		return goarch == "amd64"
 	default:
--- a/src/cmd/link/internal/ld/config.go
+++ b/src/cmd/link/internal/ld/config.go
@ -199,8 +199,8 @@ func mustLinkExternal(ctxt *Link) (res bool, reason string) {
 	// When the race flag is set, the LLVM tsan relocatable file is linked
 	// into the final binary, which means external linking is required because
 	// internal linking does not support it.
-	if *flagRace && ctxt.Arch.InFamily(sys.PPC64) {
-		return true, "race on ppc64le"
+	if *flagRace && ctxt.Arch.InFamily(sys.PPC64, sys.ARM64) {
+		return true, "race on " + objabi.GOARCH
 	}

 	// Some build modes require work the internal linker cannot do (yet).
--- a/src/race.bash
+++ b/src/race.bash
@ -9,7 +9,7 @@
 set -e

 function usage {
-	echo 'race detector is only supported on linux/amd64, linux/ppc64le, freebsd/amd64, netbsd/amd64 and darwin/amd64' 1>&2
+	echo 'race detector is only supported on linux/amd64, linux/ppc64le, linux/arm64, freebsd/amd64, netbsd/amd64 and darwin/amd64' 1>&2
 	exit 1
 }

@ -21,7 +21,7 @@ case $(uname) in
 	fi
 	;;
 "Linux")
-	if [ $(uname -m) != "x86_64" ] && [ $(uname -m) != "ppc64le" ]; then
+	if [ $(uname -m) != "x86_64" ] && [ $(uname -m) != "ppc64le" ] && [ $(uname -m) != "aarch64" ]; then
 		usage
 	fi
 	;;
--- a/src/runtime/asm_arm64.s
+++ b/src/runtime/asm_arm64.s
@ -18,7 +18,8 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	// create istack out of the given (operating system) stack.
 	// _cgo_init may update stackguard.
 	MOVD	$runtime·g0(SB), g
-	MOVD RSP, R7
+	BL	runtime·save_g(SB)
+	MOVD	RSP, R7
 	MOVD	$(-64*1024)(R7), R0
 	MOVD	R0, g_stackguard0(g)
 	MOVD	R0, g_stackguard1(g)
--- a/src/runtime/race/README
+++ b/src/runtime/race/README
@ -10,3 +10,4 @@ race_linux_amd64.syso built with LLVM fe2c72c59aa7f4afa45e3f65a5d16a374b6cce26 a
 race_linux_ppc64le.syso built with LLVM fe2c72c59aa7f4afa45e3f65a5d16a374b6cce26 and Go 323c85862a7afbde66a3bba0776bf4ba6cd7c030.
 race_netbsd_amd64.syso built with LLVM fe2c72c59aa7f4afa45e3f65a5d16a374b6cce26 and Go 323c85862a7afbde66a3bba0776bf4ba6cd7c030.
 race_windows_amd64.syso built with LLVM ae08a22cc215448aa3ad5a6fb099f6df77e9fa01 and Go 323c85862a7afbde66a3bba0776bf4ba6cd7c030.
+race_linux_arm64.syso built with LLVM 3aa2b775d08f903f804246af10b80a439c16b436 and Go ef2c48659880c7e8a989e6721a21f018790f7793.
--- a/src/runtime/race/race.go
+++ b/src/runtime/race/race.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 race,linux,amd64 race,freebsd,amd64 race,netbsd,amd64 race,darwin,amd64 race,windows,amd64 race,linux,ppc64le
+// +build race,linux,amd64 race,freebsd,amd64 race,netbsd,amd64 race,darwin,amd64 race,windows,amd64 race,linux,ppc64le race,linux,arm64

 package race

--- a/src/runtime/race/race_linux_arm64.syso
+++ b/src/runtime/race/race_linux_arm64.syso
--- a/src/runtime/race_arm64.s
+++ b/src/runtime/race_arm64.s
@ -0,0 +1,445 @@
+// Copyright 2018 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 race
+
+#include "go_asm.h"
+#include "funcdata.h"
+#include "textflag.h"
+#include "tls_arm64.h"
+
+// The following thunks allow calling the gcc-compiled race runtime directly
+// from Go code without going all the way through cgo.
+// First, it's much faster (up to 50% speedup for real Go programs).
+// Second, it eliminates race-related special cases from cgocall and scheduler.
+// Third, in long-term it will allow to remove cyclic runtime/race dependency on cmd/go.
+
+// A brief recap of the arm64 calling convention.
+// Arguments are passed in R0...R7, the rest is on stack.
+// Callee-saved registers are: R19...R28.
+// Temporary registers are: R9...R15
+// SP must be 16-byte aligned.
+
+// When calling racecalladdr, R9 is the call target address.
+
+// The race ctx, ThreadState *thr below, is passed in R0 and loaded in racecalladdr.
+
+#define load_g \
+	MRS_TPIDR_R0 \
+	MOVD    runtime·tls_g(SB), R11 \
+	ADD     R11, R0 \
+	MOVD    0(R0), g
+
+// func runtime·raceread(addr uintptr)
+// Called from instrumented code.
+TEXT	runtime·raceread(SB), NOSPLIT, $0-8
+	MOVD	addr+0(FP), R1
+	MOVD	LR, R2
+	// void __tsan_read(ThreadState *thr, void *addr, void *pc);
+	MOVD	$__tsan_read(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// func runtime·RaceRead(addr uintptr)
+TEXT	runtime·RaceRead(SB), NOSPLIT, $0-8
+	// This needs to be a tail call, because raceread reads caller pc.
+	JMP	runtime·raceread(SB)
+
+// func runtime·racereadpc(void *addr, void *callpc, void *pc)
+TEXT	runtime·racereadpc(SB), NOSPLIT, $0-24
+	MOVD	addr+0(FP), R1
+	MOVD	callpc+8(FP), R2
+	MOVD	pc+16(FP), R3
+	// void __tsan_read_pc(ThreadState *thr, void *addr, void *callpc, void *pc);
+	MOVD	$__tsan_read_pc(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// func runtime·racewrite(addr uintptr)
+// Called from instrumented code.
+TEXT	runtime·racewrite(SB), NOSPLIT, $0-8
+	MOVD	addr+0(FP), R1
+	MOVD	LR, R2
+	// void __tsan_write(ThreadState *thr, void *addr, void *pc);
+	MOVD	$__tsan_write(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// func runtime·RaceWrite(addr uintptr)
+TEXT	runtime·RaceWrite(SB), NOSPLIT, $0-8
+	// This needs to be a tail call, because racewrite reads caller pc.
+	JMP	runtime·racewrite(SB)
+
+// func runtime·racewritepc(void *addr, void *callpc, void *pc)
+TEXT	runtime·racewritepc(SB), NOSPLIT, $0-24
+	MOVD	addr+0(FP), R1
+	MOVD	callpc+8(FP), R2
+	MOVD	pc+16(FP), R3
+	// void __tsan_write_pc(ThreadState *thr, void *addr, void *callpc, void *pc);
+	MOVD	$__tsan_write_pc(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// func runtime·racereadrange(addr, size uintptr)
+// Called from instrumented code.
+TEXT	runtime·racereadrange(SB), NOSPLIT, $0-16
+	MOVD	addr+0(FP), R1
+	MOVD	size+8(FP), R2
+	MOVD	LR, R3
+	// void __tsan_read_range(ThreadState *thr, void *addr, uintptr size, void *pc);
+	MOVD	$__tsan_read_range(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// func runtime·RaceReadRange(addr, size uintptr)
+TEXT	runtime·RaceReadRange(SB), NOSPLIT, $0-16
+	// This needs to be a tail call, because racereadrange reads caller pc.
+	JMP	runtime·racereadrange(SB)
+
+// func runtime·racereadrangepc1(void *addr, uintptr sz, void *pc)
+TEXT	runtime·racereadrangepc1(SB), NOSPLIT, $0-24
+	MOVD	addr+0(FP), R1
+	MOVD	size+8(FP), R2
+	MOVD	pc+16(FP), R3
+	ADD	$4, R3	// pc is function start, tsan wants return address.
+	// void __tsan_read_range(ThreadState *thr, void *addr, uintptr size, void *pc);
+	MOVD	$__tsan_read_range(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// func runtime·racewriterange(addr, size uintptr)
+// Called from instrumented code.
+TEXT	runtime·racewriterange(SB), NOSPLIT, $0-16
+	MOVD	addr+0(FP), R1
+	MOVD	size+8(FP), R2
+	MOVD	LR, R3
+	// void __tsan_write_range(ThreadState *thr, void *addr, uintptr size, void *pc);
+	MOVD	$__tsan_write_range(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// func runtime·RaceWriteRange(addr, size uintptr)
+TEXT	runtime·RaceWriteRange(SB), NOSPLIT, $0-16
+	// This needs to be a tail call, because racewriterange reads caller pc.
+	JMP	runtime·racewriterange(SB)
+
+// func runtime·racewriterangepc1(void *addr, uintptr sz, void *pc)
+TEXT	runtime·racewriterangepc1(SB), NOSPLIT, $0-24
+	MOVD	addr+0(FP), R1
+	MOVD	size+8(FP), R2
+	MOVD	pc+16(FP), R3
+	ADD	$4, R3	// pc is function start, tsan wants return address.
+	// void __tsan_write_range(ThreadState *thr, void *addr, uintptr size, void *pc);
+	MOVD	$__tsan_write_range(SB), R9
+	JMP	racecalladdr<>(SB)
+
+// If addr (R1) is out of range, do nothing.
+// Otherwise, setup goroutine context and invoke racecall. Other arguments already set.
+TEXT	racecalladdr<>(SB), NOSPLIT, $0-0
+	load_g
+	MOVD	g_racectx(g), R0
+	// Check that addr is within [arenastart, arenaend) or within [racedatastart, racedataend).
+	MOVD	runtime·racearenastart(SB), R10
+	CMP	R10, R1
+	BLT	data
+	MOVD	runtime·racearenaend(SB), R10
+	CMP	R10, R1
+	BLT	call
+data:
+	MOVD	runtime·racedatastart(SB), R10
+	CMP	R10, R1
+	BLT	ret
+	MOVD	runtime·racedataend(SB), R10
+	CMP	R10, R1
+	BGT	ret
+call:
+	JMP	racecall<>(SB)
+ret:
+	RET
+
+// func runtime·racefuncenterfp(fp uintptr)
+// Called from instrumented code.
+// Like racefuncenter but doesn't passes an arg, uses the caller pc
+// from the first slot on the stack
+TEXT	runtime·racefuncenterfp(SB), NOSPLIT, $0-0
+	MOVD	0(RSP), R9
+	JMP	racefuncenter<>(SB)
+
+// func runtime·racefuncenter(pc uintptr)
+// Called from instrumented code.
+TEXT	runtime·racefuncenter(SB), NOSPLIT, $0-8
+	MOVD	callpc+0(FP), R9
+	JMP	racefuncenter<>(SB)
+
+// Common code for racefuncenter/racefuncenterfp
+// R9 = caller's return address
+TEXT	racefuncenter<>(SB), NOSPLIT, $0-0
+	load_g
+	MOVD	g_racectx(g), R0	// goroutine racectx
+	MOVD	R9, R1
+	// void __tsan_func_enter(ThreadState *thr, void *pc);
+	MOVD	$__tsan_func_enter(SB), R9
+	BL	racecall<>(SB)
+	RET
+
+// func runtime·racefuncexit()
+// Called from instrumented code.
+TEXT	runtime·racefuncexit(SB), NOSPLIT, $0-0
+	load_g
+	MOVD	g_racectx(g), R0	// race context
+	// void __tsan_func_exit(ThreadState *thr);
+	MOVD	$__tsan_func_exit(SB), R9
+	JMP	racecall<>(SB)
+
+// Atomic operations for sync/atomic package.
+// R3 = addr of arguments passed to this function, it can
+// be fetched at 40(RSP) in racecallatomic after two times BL
+// R0, R1, R2 set in racecallatomic
+
+// Load
+TEXT	sync∕atomic·LoadInt32(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic32_load(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·LoadInt64(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic64_load(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·LoadUint32(SB), NOSPLIT, $0
+	JMP	sync∕atomic·LoadInt32(SB)
+
+TEXT	sync∕atomic·LoadUint64(SB), NOSPLIT, $0
+	JMP	sync∕atomic·LoadInt64(SB)
+
+TEXT	sync∕atomic·LoadUintptr(SB), NOSPLIT, $0
+	JMP	sync∕atomic·LoadInt64(SB)
+
+TEXT	sync∕atomic·LoadPointer(SB), NOSPLIT, $0
+	JMP	sync∕atomic·LoadInt64(SB)
+
+// Store
+TEXT	sync∕atomic·StoreInt32(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic32_store(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·StoreInt64(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic64_store(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·StoreUint32(SB), NOSPLIT, $0
+	JMP	sync∕atomic·StoreInt32(SB)
+
+TEXT	sync∕atomic·StoreUint64(SB), NOSPLIT, $0
+	JMP	sync∕atomic·StoreInt64(SB)
+
+TEXT	sync∕atomic·StoreUintptr(SB), NOSPLIT, $0
+	JMP	sync∕atomic·StoreInt64(SB)
+
+// Swap
+TEXT	sync∕atomic·SwapInt32(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic32_exchange(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·SwapInt64(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic64_exchange(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·SwapUint32(SB), NOSPLIT, $0
+	JMP	sync∕atomic·SwapInt32(SB)
+
+TEXT	sync∕atomic·SwapUint64(SB), NOSPLIT, $0
+	JMP	sync∕atomic·SwapInt64(SB)
+
+TEXT	sync∕atomic·SwapUintptr(SB), NOSPLIT, $0
+	JMP	sync∕atomic·SwapInt64(SB)
+
+// Add
+TEXT	sync∕atomic·AddInt32(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic32_fetch_add(SB), R9
+	BL	racecallatomic<>(SB)
+	MOVW	add+8(FP), R0	// convert fetch_add to add_fetch
+	MOVW	ret+16(FP), R1
+	ADD	R0, R1, R0
+	MOVW	R0, ret+16(FP)
+	RET
+
+TEXT	sync∕atomic·AddInt64(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic64_fetch_add(SB), R9
+	BL	racecallatomic<>(SB)
+	MOVD	add+8(FP), R0	// convert fetch_add to add_fetch
+	MOVD	ret+16(FP), R1
+	ADD	R0, R1, R0
+	MOVD	R0, ret+16(FP)
+	RET
+
+TEXT	sync∕atomic·AddUint32(SB), NOSPLIT, $0
+	JMP	sync∕atomic·AddInt32(SB)
+
+TEXT	sync∕atomic·AddUint64(SB), NOSPLIT, $0
+	JMP	sync∕atomic·AddInt64(SB)
+
+TEXT	sync∕atomic·AddUintptr(SB), NOSPLIT, $0
+	JMP	sync∕atomic·AddInt64(SB)
+
+// CompareAndSwap
+TEXT	sync∕atomic·CompareAndSwapInt32(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic32_compare_exchange(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·CompareAndSwapInt64(SB), NOSPLIT, $0
+	MOVD	$__tsan_go_atomic64_compare_exchange(SB), R9
+	BL	racecallatomic<>(SB)
+	RET
+
+TEXT	sync∕atomic·CompareAndSwapUint32(SB), NOSPLIT, $0
+	JMP	sync∕atomic·CompareAndSwapInt32(SB)
+
+TEXT	sync∕atomic·CompareAndSwapUint64(SB), NOSPLIT, $0
+	JMP	sync∕atomic·CompareAndSwapInt64(SB)
+
+TEXT	sync∕atomic·CompareAndSwapUintptr(SB), NOSPLIT, $0
+	JMP	sync∕atomic·CompareAndSwapInt64(SB)
+
+// Generic atomic operation implementation.
+// R9 = addr of target function
+TEXT	racecallatomic<>(SB), NOSPLIT, $0
+	// Set up these registers
+	// R0 = *ThreadState
+	// R1 = caller pc
+	// R2 = pc
+	// R3 = addr of incoming arg list
+
+	// Trigger SIGSEGV early.
+	MOVD	40(RSP), R3	// 1st arg is addr. after two times BL, get it at 40(RSP)
+	MOVD	(R3), R13	// segv here if addr is bad
+	// Check that addr is within [arenastart, arenaend) or within [racedatastart, racedataend).
+	MOVD	runtime·racearenastart(SB), R10
+	CMP	R10, R3
+	BLT	racecallatomic_data
+	MOVD	runtime·racearenaend(SB), R10
+	CMP	R10, R3
+	BLT	racecallatomic_ok
+racecallatomic_data:
+	MOVD	runtime·racedatastart(SB), R10
+	CMP	R10, R3
+	BLT	racecallatomic_ignore
+	MOVD	runtime·racedataend(SB), R10
+	CMP	R10, R3
+	BGE	racecallatomic_ignore
+racecallatomic_ok:
+	// Addr is within the good range, call the atomic function.
+	load_g
+	MOVD	g_racectx(g), R0	// goroutine context
+	MOVD	16(RSP), R1	// caller pc
+	MOVD	R9, R2	// pc
+	ADD	$40, RSP, R3
+	JMP	racecall<>(SB)	// does not return
+racecallatomic_ignore:
+	// Addr is outside the good range.
+	// Call __tsan_go_ignore_sync_begin to ignore synchronization during the atomic op.
+	// An attempt to synchronize on the address would cause crash.
+	MOVD	R9, R20	// remember the original function
+	MOVD	$__tsan_go_ignore_sync_begin(SB), R9
+	load_g
+	MOVD	g_racectx(g), R0	// goroutine context
+	BL	racecall<>(SB)
+	MOVD	R20, R9	// restore the original function
+	// Call the atomic function.
+	// racecall will call LLVM race code which might clobber R28 (g)
+	load_g
+	MOVD	g_racectx(g), R0	// goroutine context
+	MOVD	16(RSP), R1	// caller pc
+	MOVD	R9, R2	// pc
+	ADD	$40, RSP, R3	// arguments
+	BL	racecall<>(SB)
+	// Call __tsan_go_ignore_sync_end.
+	MOVD	$__tsan_go_ignore_sync_end(SB), R9
+	MOVD	g_racectx(g), R0	// goroutine context
+	BL	racecall<>(SB)
+	RET
+
+// func runtime·racecall(void(*f)(...), ...)
+// Calls C function f from race runtime and passes up to 4 arguments to it.
+// The arguments are never heap-object-preserving pointers, so we pretend there are no arguments.
+TEXT	runtime·racecall(SB), NOSPLIT, $0-0
+	MOVD	fn+0(FP), R9
+	MOVD	arg0+8(FP), R0
+	MOVD	arg1+16(FP), R1
+	MOVD	arg2+24(FP), R2
+	MOVD	arg3+32(FP), R3
+	JMP	racecall<>(SB)
+
+// Switches SP to g0 stack and calls (R9). Arguments already set.
+TEXT	racecall<>(SB), NOSPLIT, $0-0
+	MOVD	g_m(g), R10
+	// Switch to g0 stack.
+	MOVD	RSP, R19	// callee-saved, preserved across the CALL
+	MOVD	m_g0(R10), R11
+	CMP	R11, g
+	BEQ	call	// already on g0
+	MOVD	(g_sched+gobuf_sp)(R11), R12
+	MOVD	R12, RSP
+call:
+	BL	R9
+	MOVD	R19, RSP
+	RET
+
+// C->Go callback thunk that allows to call runtime·racesymbolize from C code.
+// Direct Go->C race call has only switched SP, finish g->g0 switch by setting correct g.
+// The overall effect of Go->C->Go call chain is similar to that of mcall.
+// R0 contains command code. R1 contains command-specific context.
+// See racecallback for command codes.
+TEXT	runtime·racecallbackthunk(SB), NOSPLIT|NOFRAME, $0
+	// Handle command raceGetProcCmd (0) here.
+	// First, code below assumes that we are on curg, while raceGetProcCmd
+	// can be executed on g0. Second, it is called frequently, so will
+	// benefit from this fast path.
+	CMP	$0, R0
+	BNE	rest
+	MOVD	g, R13
+	load_g
+	MOVD	g_m(g), R0
+	MOVD	m_p(R0), R0
+	MOVD	p_racectx(R0), R0
+	MOVD	R0, (R1)
+	MOVD	R13, g
+	JMP	(LR)
+rest:
+        // Save callee-saved registers (Go code won't respect that).
+	// 8(RSP) and 16(RSP) are for args passed through racecallback
+	SUB	$96, RSP
+	MOVD	LR, 0(RSP)
+	STP	(R19, R20), 24(RSP)
+	STP	(R21, R22), 40(RSP)
+	STP	(R23, R24), 56(RSP)
+	STP	(R25, R26), 72(RSP)
+	MOVD	R27, 88(RSP)
+	// Set g = g0.
+	// load_g will clobber R0, Save R0
+	MOVD	R0, R13
+	load_g
+	// restore R0
+	MOVD	R13, R0
+	MOVD	g_m(g), R13
+	MOVD	m_g0(R13), g
+
+	MOVD	R0, 8(RSP)	// func arg
+	MOVD	R1, 16(RSP)	// func arg
+	BL	runtime·racecallback(SB)
+
+	// All registers are smashed after Go code, reload.
+	MOVD	g_m(g), R13
+	MOVD	m_curg(R13), g	// g = m->curg
+	// Restore callee-saved registers.
+	MOVD	0(RSP), LR
+	LDP	24(RSP), (R19, R20)
+	LDP	40(RSP), (R21, R22)
+	LDP	56(RSP), (R23, R24)
+	LDP	72(RSP), (R25, R26)
+	MOVD	88(RSP), R27
+	ADD	$96, RSP
+	JMP	(LR)
+
+// tls_g, g value for each thread in TLS
+GLOBL runtime·tls_g+0(SB), TLSBSS+DUPOK, $8