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Diffstat (limited to '')
-rw-r--r-- | src/runtime/race_ppc64le.s | 601 |
1 files changed, 601 insertions, 0 deletions
diff --git a/src/runtime/race_ppc64le.s b/src/runtime/race_ppc64le.s new file mode 100644 index 0000000..ac335b1 --- /dev/null +++ b/src/runtime/race_ppc64le.s @@ -0,0 +1,601 @@ +// 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. + +//go:build race + +#include "go_asm.h" +#include "go_tls.h" +#include "funcdata.h" +#include "textflag.h" +#include "asm_ppc64x.h" + +// The following functions allow calling the clang-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 ppc64le calling convention. +// Arguments are passed in R3, R4, R5 ... +// SP must be 16-byte aligned. + +// Note that for ppc64x, LLVM follows the standard ABI and +// expects arguments in registers, so these functions move +// the arguments from storage to the registers expected +// by the ABI. + +// When calling from Go to Clang tsan code: +// R3 is the 1st argument and is usually the ThreadState* +// R4-? are the 2nd, 3rd, 4th, etc. arguments + +// When calling racecalladdr: +// R8 is the call target address + +// The race ctx is passed in R3 and loaded in +// racecalladdr. +// +// The sequence used to get the race ctx: +// MOVD runtime·tls_g(SB), R10 // Address of TLS variable +// MOVD 0(R10), g // g = R30 +// MOVD g_racectx(g), R3 // racectx == ThreadState + +// func runtime·RaceRead(addr uintptr) +// Called from instrumented Go code +TEXT runtime·raceread<ABIInternal>(SB), NOSPLIT, $0-8 + MOVD R3, R4 // addr + MOVD LR, R5 // caller of this? + // void __tsan_read(ThreadState *thr, void *addr, void *pc); + MOVD $__tsan_read(SB), R8 + BR racecalladdr<>(SB) + +TEXT runtime·RaceRead(SB), NOSPLIT, $0-8 + BR runtime·raceread(SB) + +// void runtime·racereadpc(void *addr, void *callpc, void *pc) +TEXT runtime·racereadpc(SB), NOSPLIT, $0-24 + MOVD addr+0(FP), R4 + MOVD callpc+8(FP), R5 + MOVD pc+16(FP), R6 + // void __tsan_read_pc(ThreadState *thr, void *addr, void *callpc, void *pc); + MOVD $__tsan_read_pc(SB), R8 + BR racecalladdr<>(SB) + +// func runtime·RaceWrite(addr uintptr) +// Called from instrumented Go code +TEXT runtime·racewrite<ABIInternal>(SB), NOSPLIT, $0-8 + MOVD R3, R4 // addr + MOVD LR, R5 // caller has set LR via BL inst + // void __tsan_write(ThreadState *thr, void *addr, void *pc); + MOVD $__tsan_write(SB), R8 + BR racecalladdr<>(SB) + +TEXT runtime·RaceWrite(SB), NOSPLIT, $0-8 + JMP runtime·racewrite(SB) + +// void runtime·racewritepc(void *addr, void *callpc, void *pc) +TEXT runtime·racewritepc(SB), NOSPLIT, $0-24 + MOVD addr+0(FP), R4 + MOVD callpc+8(FP), R5 + MOVD pc+16(FP), R6 + // void __tsan_write_pc(ThreadState *thr, void *addr, void *callpc, void *pc); + MOVD $__tsan_write_pc(SB), R8 + BR racecalladdr<>(SB) + +// func runtime·RaceReadRange(addr, size uintptr) +// Called from instrumented Go code. +TEXT runtime·racereadrange<ABIInternal>(SB), NOSPLIT, $0-16 + MOVD R4, R5 // size + MOVD R3, R4 // addr + MOVD LR, R6 + // void __tsan_read_range(ThreadState *thr, void *addr, uintptr size, void *pc); + MOVD $__tsan_read_range(SB), R8 + BR racecalladdr<>(SB) + +// void runtime·racereadrangepc1(void *addr, uintptr sz, void *pc) +TEXT runtime·racereadrangepc1(SB), NOSPLIT, $0-24 + MOVD addr+0(FP), R4 + MOVD size+8(FP), R5 + MOVD pc+16(FP), R6 + ADD $4, R6 // tsan wants return addr + // void __tsan_read_range(ThreadState *thr, void *addr, uintptr size, void *pc); + MOVD $__tsan_read_range(SB), R8 + BR racecalladdr<>(SB) + +TEXT runtime·RaceReadRange(SB), NOSPLIT, $0-16 + BR runtime·racereadrange(SB) + +// func runtime·RaceWriteRange(addr, size uintptr) +// Called from instrumented Go code. +TEXT runtime·racewriterange<ABIInternal>(SB), NOSPLIT, $0-16 + MOVD R4, R5 // size + MOVD R3, R4 // addr + MOVD LR, R6 + // void __tsan_write_range(ThreadState *thr, void *addr, uintptr size, void *pc); + MOVD $__tsan_write_range(SB), R8 + BR racecalladdr<>(SB) + +TEXT runtime·RaceWriteRange(SB), NOSPLIT, $0-16 + BR runtime·racewriterange(SB) + +// void runtime·racewriterangepc1(void *addr, uintptr sz, void *pc) +// Called from instrumented Go code +TEXT runtime·racewriterangepc1(SB), NOSPLIT, $0-24 + MOVD addr+0(FP), R4 + MOVD size+8(FP), R5 + MOVD pc+16(FP), R6 + ADD $4, R6 // add 4 to inst offset? + // void __tsan_write_range(ThreadState *thr, void *addr, uintptr size, void *pc); + MOVD $__tsan_write_range(SB), R8 + BR racecalladdr<>(SB) + +// Call a __tsan function from Go code. +// R8 = tsan function address +// R3 = *ThreadState a.k.a. g_racectx from g +// R4 = addr passed to __tsan function +// +// Otherwise, setup goroutine context and invoke racecall. Other arguments already set. +TEXT racecalladdr<>(SB), NOSPLIT, $0-0 + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + MOVD g_racectx(g), R3 // goroutine context + // Check that addr is within [arenastart, arenaend) or within [racedatastart, racedataend). + MOVD runtime·racearenastart(SB), R9 + CMP R4, R9 + BLT data + MOVD runtime·racearenaend(SB), R9 + CMP R4, R9 + BLT call +data: + MOVD runtime·racedatastart(SB), R9 + CMP R4, R9 + BLT ret + MOVD runtime·racedataend(SB), R9 + CMP R4, R9 + BGT ret +call: + // Careful!! racecall will save LR on its + // stack, which is OK as long as racecalladdr + // doesn't change in a way that generates a stack. + // racecall should return to the caller of + // recalladdr. + BR racecall<>(SB) +ret: + RET + +// func runtime·racefuncenter(pc uintptr) +// Called from instrumented Go code. +TEXT runtime·racefuncenter(SB), NOSPLIT, $0-8 + MOVD callpc+0(FP), R8 + BR racefuncenter<>(SB) + +// Common code for racefuncenter +// R11 = caller's return address +TEXT racefuncenter<>(SB), NOSPLIT, $0-0 + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + MOVD g_racectx(g), R3 // goroutine racectx aka *ThreadState + MOVD R8, R4 // caller pc set by caller in R8 + // void __tsan_func_enter(ThreadState *thr, void *pc); + MOVD $__tsan_func_enter(SB), R8 + BR racecall<>(SB) + RET + +// func runtime·racefuncexit() +// Called from Go instrumented code. +TEXT runtime·racefuncexit(SB), NOSPLIT, $0-0 + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + MOVD g_racectx(g), R3 // goroutine racectx aka *ThreadState + // void __tsan_func_exit(ThreadState *thr); + MOVD $__tsan_func_exit(SB), R8 + BR racecall<>(SB) + +// Atomic operations for sync/atomic package. +// Some use the __tsan versions instead +// R6 = addr of arguments passed to this function +// R3, R4, R5 set in racecallatomic + +// Load atomic in tsan +TEXT sync∕atomic·LoadInt32(SB), NOSPLIT, $0-12 + GO_ARGS + // void __tsan_go_atomic32_load(ThreadState *thr, uptr cpc, uptr pc, u8 *a); + MOVD $__tsan_go_atomic32_load(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + RET + +TEXT sync∕atomic·LoadInt64(SB), NOSPLIT, $0-16 + GO_ARGS + // void __tsan_go_atomic64_load(ThreadState *thr, uptr cpc, uptr pc, u8 *a); + MOVD $__tsan_go_atomic64_load(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + RET + +TEXT sync∕atomic·LoadUint32(SB), NOSPLIT, $0-12 + GO_ARGS + BR sync∕atomic·LoadInt32(SB) + +TEXT sync∕atomic·LoadUint64(SB), NOSPLIT, $0-16 + GO_ARGS + BR sync∕atomic·LoadInt64(SB) + +TEXT sync∕atomic·LoadUintptr(SB), NOSPLIT, $0-16 + GO_ARGS + BR sync∕atomic·LoadInt64(SB) + +TEXT sync∕atomic·LoadPointer(SB), NOSPLIT, $0-16 + GO_ARGS + BR sync∕atomic·LoadInt64(SB) + +// Store atomic in tsan +TEXT sync∕atomic·StoreInt32(SB), NOSPLIT, $0-12 + GO_ARGS + // void __tsan_go_atomic32_store(ThreadState *thr, uptr cpc, uptr pc, u8 *a); + MOVD $__tsan_go_atomic32_store(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + +TEXT sync∕atomic·StoreInt64(SB), NOSPLIT, $0-16 + GO_ARGS + // void __tsan_go_atomic64_store(ThreadState *thr, uptr cpc, uptr pc, u8 *a); + MOVD $__tsan_go_atomic64_store(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + +TEXT sync∕atomic·StoreUint32(SB), NOSPLIT, $0-12 + GO_ARGS + BR sync∕atomic·StoreInt32(SB) + +TEXT sync∕atomic·StoreUint64(SB), NOSPLIT, $0-16 + GO_ARGS + BR sync∕atomic·StoreInt64(SB) + +TEXT sync∕atomic·StoreUintptr(SB), NOSPLIT, $0-16 + GO_ARGS + BR sync∕atomic·StoreInt64(SB) + +// Swap in tsan +TEXT sync∕atomic·SwapInt32(SB), NOSPLIT, $0-20 + GO_ARGS + // void __tsan_go_atomic32_exchange(ThreadState *thr, uptr cpc, uptr pc, u8 *a); + MOVD $__tsan_go_atomic32_exchange(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + +TEXT sync∕atomic·SwapInt64(SB), NOSPLIT, $0-24 + GO_ARGS + // void __tsan_go_atomic64_exchange(ThreadState *thr, uptr cpc, uptr pc, u8 *a) + MOVD $__tsan_go_atomic64_exchange(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + +TEXT sync∕atomic·SwapUint32(SB), NOSPLIT, $0-20 + GO_ARGS + BR sync∕atomic·SwapInt32(SB) + +TEXT sync∕atomic·SwapUint64(SB), NOSPLIT, $0-24 + GO_ARGS + BR sync∕atomic·SwapInt64(SB) + +TEXT sync∕atomic·SwapUintptr(SB), NOSPLIT, $0-24 + GO_ARGS + BR sync∕atomic·SwapInt64(SB) + +// Add atomic in tsan +TEXT sync∕atomic·AddInt32(SB), NOSPLIT, $0-20 + GO_ARGS + // void __tsan_go_atomic32_fetch_add(ThreadState *thr, uptr cpc, uptr pc, u8 *a); + MOVD $__tsan_go_atomic32_fetch_add(SB), R8 + ADD $64, R1, R6 // addr of caller's 1st arg + BL racecallatomic<>(SB) + // The tsan fetch_add result is not as expected by Go, + // so the 'add' must be added to the result. + MOVW add+8(FP), R3 // The tsa fetch_add does not return the + MOVW ret+16(FP), R4 // result as expected by go, so fix it. + ADD R3, R4, R3 + MOVW R3, ret+16(FP) + RET + +TEXT sync∕atomic·AddInt64(SB), NOSPLIT, $0-24 + GO_ARGS + // void __tsan_go_atomic64_fetch_add(ThreadState *thr, uptr cpc, uptr pc, u8 *a); + MOVD $__tsan_go_atomic64_fetch_add(SB), R8 + ADD $64, R1, R6 // addr of caller's 1st arg + BL racecallatomic<>(SB) + // The tsan fetch_add result is not as expected by Go, + // so the 'add' must be added to the result. + MOVD add+8(FP), R3 + MOVD ret+16(FP), R4 + ADD R3, R4, R3 + MOVD R3, ret+16(FP) + RET + +TEXT sync∕atomic·AddUint32(SB), NOSPLIT, $0-20 + GO_ARGS + BR sync∕atomic·AddInt32(SB) + +TEXT sync∕atomic·AddUint64(SB), NOSPLIT, $0-24 + GO_ARGS + BR sync∕atomic·AddInt64(SB) + +TEXT sync∕atomic·AddUintptr(SB), NOSPLIT, $0-24 + GO_ARGS + BR sync∕atomic·AddInt64(SB) + +// CompareAndSwap in tsan +TEXT sync∕atomic·CompareAndSwapInt32(SB), NOSPLIT, $0-17 + GO_ARGS + // void __tsan_go_atomic32_compare_exchange( + // ThreadState *thr, uptr cpc, uptr pc, u8 *a) + MOVD $__tsan_go_atomic32_compare_exchange(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + +TEXT sync∕atomic·CompareAndSwapInt64(SB), NOSPLIT, $0-25 + GO_ARGS + // void __tsan_go_atomic32_compare_exchange( + // ThreadState *thr, uptr cpc, uptr pc, u8 *a) + MOVD $__tsan_go_atomic64_compare_exchange(SB), R8 + ADD $32, R1, R6 // addr of caller's 1st arg + BR racecallatomic<>(SB) + +TEXT sync∕atomic·CompareAndSwapUint32(SB), NOSPLIT, $0-17 + GO_ARGS + BR sync∕atomic·CompareAndSwapInt32(SB) + +TEXT sync∕atomic·CompareAndSwapUint64(SB), NOSPLIT, $0-25 + GO_ARGS + BR sync∕atomic·CompareAndSwapInt64(SB) + +TEXT sync∕atomic·CompareAndSwapUintptr(SB), NOSPLIT, $0-25 + GO_ARGS + BR sync∕atomic·CompareAndSwapInt64(SB) + +// Common function used to call tsan's atomic functions +// R3 = *ThreadState +// R4 = TODO: What's this supposed to be? +// R5 = caller pc +// R6 = addr of incoming arg list +// R8 contains addr of target function. +TEXT racecallatomic<>(SB), NOSPLIT, $0-0 + // Trigger SIGSEGV early if address passed to atomic function is bad. + MOVD (R6), R7 // 1st arg is addr + MOVD (R7), R9 // segv here if addr is bad + // Check that addr is within [arenastart, arenaend) or within [racedatastart, racedataend). + MOVD runtime·racearenastart(SB), R9 + CMP R7, R9 + BLT racecallatomic_data + MOVD runtime·racearenaend(SB), R9 + CMP R7, R9 + BLT racecallatomic_ok +racecallatomic_data: + MOVD runtime·racedatastart(SB), R9 + CMP R7, R9 + BLT racecallatomic_ignore + MOVD runtime·racedataend(SB), R9 + CMP R7, R9 + BGE racecallatomic_ignore +racecallatomic_ok: + // Addr is within the good range, call the atomic function. + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + MOVD g_racectx(g), R3 // goroutine racectx aka *ThreadState + MOVD R8, R5 // pc is the function called + MOVD (R1), R4 // caller pc from stack + BL racecall<>(SB) // BL needed to maintain stack consistency + RET // +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 R8, R15 // save the original function + MOVD R6, R17 // save the original arg list addr + MOVD $__tsan_go_ignore_sync_begin(SB), R8 // func addr to call + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + MOVD g_racectx(g), R3 // goroutine context + BL racecall<>(SB) + MOVD R15, R8 // restore the original function + MOVD R17, R6 // restore arg list addr + // Call the atomic function. + // racecall will call LLVM race code which might clobber r30 (g) + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + + MOVD g_racectx(g), R3 + MOVD R8, R4 // pc being called same TODO as above + MOVD (R1), R5 // caller pc from latest LR + BL racecall<>(SB) + // Call __tsan_go_ignore_sync_end. + MOVD $__tsan_go_ignore_sync_end(SB), R8 + MOVD g_racectx(g), R3 // goroutine context g should still be good? + BL racecall<>(SB) + RET + +// void 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), R8 + MOVD arg0+8(FP), R3 + MOVD arg1+16(FP), R4 + MOVD arg2+24(FP), R5 + MOVD arg3+32(FP), R6 + JMP racecall<>(SB) + +// Finds g0 and sets its stack +// Arguments were loaded for call from Go to C +TEXT racecall<>(SB), NOSPLIT, $0-0 + // Set the LR slot for the ppc64 ABI + MOVD LR, R10 + MOVD R10, 0(R1) // Go expectation + MOVD R10, 16(R1) // C ABI + // Get info from the current goroutine + MOVD runtime·tls_g(SB), R10 // g offset in TLS + MOVD 0(R10), g + MOVD g_m(g), R7 // m for g + MOVD R1, R16 // callee-saved, preserved across C call + MOVD m_g0(R7), R10 // g0 for m + CMP R10, g // same g0? + BEQ call // already on g0 + MOVD (g_sched+gobuf_sp)(R10), R1 // switch R1 +call: + // prepare frame for C ABI + SUB $32, R1 // create frame for callee saving LR, CR, R2 etc. + RLDCR $0, R1, $~15, R1 // align SP to 16 bytes + MOVD R8, CTR // R8 = caller addr + MOVD R8, R12 // expected by PPC64 ABI + BL (CTR) + XOR R0, R0 // clear R0 on return from Clang + MOVD R16, R1 // restore R1; R16 nonvol in Clang + MOVD runtime·tls_g(SB), R10 // find correct g + MOVD 0(R10), g + MOVD 16(R1), R10 // LR was saved away, restore for return + MOVD R10, LR + 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. +// RARG0 contains command code. RARG1 contains command-specific context. +// See racecallback for command codes. +TEXT runtime·racecallbackthunk(SB), NOSPLIT, $-8 + // 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. + XOR R0, R0 // clear R0 since we came from C code + CMP R3, $0 + BNE rest + // g0 TODO: Don't modify g here since R30 is nonvolatile + MOVD g, R9 + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + MOVD g_m(g), R3 + MOVD m_p(R3), R3 + MOVD p_raceprocctx(R3), R3 + MOVD R3, (R4) + MOVD R9, g // restore R30 ?? + RET + + // This is all similar to what cgo does + // Save registers according to the ppc64 ABI +rest: + MOVD LR, R10 // save link register + MOVD R10, 16(R1) + MOVW CR, R10 + MOVW R10, 8(R1) + MOVDU R1, -336(R1) // Allocate frame needed for outargs and register save area + + MOVD R14, 328(R1) + MOVD R15, 48(R1) + MOVD R16, 56(R1) + MOVD R17, 64(R1) + MOVD R18, 72(R1) + MOVD R19, 80(R1) + MOVD R20, 88(R1) + MOVD R21, 96(R1) + MOVD R22, 104(R1) + MOVD R23, 112(R1) + MOVD R24, 120(R1) + MOVD R25, 128(R1) + MOVD R26, 136(R1) + MOVD R27, 144(R1) + MOVD R28, 152(R1) + MOVD R29, 160(R1) + MOVD g, 168(R1) // R30 + MOVD R31, 176(R1) + FMOVD F14, 184(R1) + FMOVD F15, 192(R1) + FMOVD F16, 200(R1) + FMOVD F17, 208(R1) + FMOVD F18, 216(R1) + FMOVD F19, 224(R1) + FMOVD F20, 232(R1) + FMOVD F21, 240(R1) + FMOVD F22, 248(R1) + FMOVD F23, 256(R1) + FMOVD F24, 264(R1) + FMOVD F25, 272(R1) + FMOVD F26, 280(R1) + FMOVD F27, 288(R1) + FMOVD F28, 296(R1) + FMOVD F29, 304(R1) + FMOVD F30, 312(R1) + FMOVD F31, 320(R1) + + MOVD R3, FIXED_FRAME+0(R1) + MOVD R4, FIXED_FRAME+8(R1) + + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + + MOVD g_m(g), R7 + MOVD m_g0(R7), R8 + CMP g, R8 + BEQ noswitch + + MOVD R8, g // set g = m-> g0 + + BL runtime·racecallback(SB) + + // All registers are clobbered after Go code, reload. + MOVD runtime·tls_g(SB), R10 + MOVD 0(R10), g + + MOVD g_m(g), R7 + MOVD m_curg(R7), g // restore g = m->curg + +ret: + MOVD 328(R1), R14 + MOVD 48(R1), R15 + MOVD 56(R1), R16 + MOVD 64(R1), R17 + MOVD 72(R1), R18 + MOVD 80(R1), R19 + MOVD 88(R1), R20 + MOVD 96(R1), R21 + MOVD 104(R1), R22 + MOVD 112(R1), R23 + MOVD 120(R1), R24 + MOVD 128(R1), R25 + MOVD 136(R1), R26 + MOVD 144(R1), R27 + MOVD 152(R1), R28 + MOVD 160(R1), R29 + MOVD 168(R1), g // R30 + MOVD 176(R1), R31 + FMOVD 184(R1), F14 + FMOVD 192(R1), F15 + FMOVD 200(R1), F16 + FMOVD 208(R1), F17 + FMOVD 216(R1), F18 + FMOVD 224(R1), F19 + FMOVD 232(R1), F20 + FMOVD 240(R1), F21 + FMOVD 248(R1), F22 + FMOVD 256(R1), F23 + FMOVD 264(R1), F24 + FMOVD 272(R1), F25 + FMOVD 280(R1), F26 + FMOVD 288(R1), F27 + FMOVD 296(R1), F28 + FMOVD 304(R1), F29 + FMOVD 312(R1), F30 + FMOVD 320(R1), F31 + + ADD $336, R1 + MOVD 8(R1), R10 + MOVFL R10, $0xff // Restore of CR + MOVD 16(R1), R10 // needed? + MOVD R10, LR + RET + +noswitch: + BL runtime·racecallback(SB) + JMP ret + +// tls_g, g value for each thread in TLS +GLOBL runtime·tls_g+0(SB), TLSBSS+DUPOK, $8 |