github.com/karrick/go@v0.0.0-20170817181416-d5b0ec858b37/src/runtime/stubs.go (about) 1 // Copyright 2014 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package runtime 6 7 import ( 8 "runtime/internal/sys" 9 "unsafe" 10 ) 11 12 // Should be a built-in for unsafe.Pointer? 13 //go:nosplit 14 func add(p unsafe.Pointer, x uintptr) unsafe.Pointer { 15 return unsafe.Pointer(uintptr(p) + x) 16 } 17 18 // getg returns the pointer to the current g. 19 // The compiler rewrites calls to this function into instructions 20 // that fetch the g directly (from TLS or from the dedicated register). 21 func getg() *g 22 23 // mcall switches from the g to the g0 stack and invokes fn(g), 24 // where g is the goroutine that made the call. 25 // mcall saves g's current PC/SP in g->sched so that it can be restored later. 26 // It is up to fn to arrange for that later execution, typically by recording 27 // g in a data structure, causing something to call ready(g) later. 28 // mcall returns to the original goroutine g later, when g has been rescheduled. 29 // fn must not return at all; typically it ends by calling schedule, to let the m 30 // run other goroutines. 31 // 32 // mcall can only be called from g stacks (not g0, not gsignal). 33 // 34 // This must NOT be go:noescape: if fn is a stack-allocated closure, 35 // fn puts g on a run queue, and g executes before fn returns, the 36 // closure will be invalidated while it is still executing. 37 func mcall(fn func(*g)) 38 39 // systemstack runs fn on a system stack. 40 // If systemstack is called from the per-OS-thread (g0) stack, or 41 // if systemstack is called from the signal handling (gsignal) stack, 42 // systemstack calls fn directly and returns. 43 // Otherwise, systemstack is being called from the limited stack 44 // of an ordinary goroutine. In this case, systemstack switches 45 // to the per-OS-thread stack, calls fn, and switches back. 46 // It is common to use a func literal as the argument, in order 47 // to share inputs and outputs with the code around the call 48 // to system stack: 49 // 50 // ... set up y ... 51 // systemstack(func() { 52 // x = bigcall(y) 53 // }) 54 // ... use x ... 55 // 56 //go:noescape 57 func systemstack(fn func()) 58 59 func badsystemstack() { 60 throw("systemstack called from unexpected goroutine") 61 } 62 63 // memclrNoHeapPointers clears n bytes starting at ptr. 64 // 65 // Usually you should use typedmemclr. memclrNoHeapPointers should be 66 // used only when the caller knows that *ptr contains no heap pointers 67 // because either: 68 // 69 // 1. *ptr is initialized memory and its type is pointer-free. 70 // 71 // 2. *ptr is uninitialized memory (e.g., memory that's being reused 72 // for a new allocation) and hence contains only "junk". 73 // 74 // in memclr_*.s 75 //go:noescape 76 func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr) 77 78 //go:linkname reflect_memclrNoHeapPointers reflect.memclrNoHeapPointers 79 func reflect_memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr) { 80 memclrNoHeapPointers(ptr, n) 81 } 82 83 // memmove copies n bytes from "from" to "to". 84 // in memmove_*.s 85 //go:noescape 86 func memmove(to, from unsafe.Pointer, n uintptr) 87 88 //go:linkname reflect_memmove reflect.memmove 89 func reflect_memmove(to, from unsafe.Pointer, n uintptr) { 90 memmove(to, from, n) 91 } 92 93 // exported value for testing 94 var hashLoad = float32(loadFactorNum) / float32(loadFactorDen) 95 96 //go:nosplit 97 func fastrand() uint32 { 98 mp := getg().m 99 fr := mp.fastrand 100 mx := uint32(int32(fr)>>31) & 0xa8888eef 101 fr = fr<<1 ^ mx 102 mp.fastrand = fr 103 return fr 104 } 105 106 //go:nosplit 107 func fastrandn(n uint32) uint32 { 108 // This is similar to fastrand() % n, but faster. 109 // See http://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/ 110 return uint32(uint64(fastrand()) * uint64(n) >> 32) 111 } 112 113 //go:linkname sync_fastrand sync.fastrand 114 func sync_fastrand() uint32 { return fastrand() } 115 116 // in asm_*.s 117 //go:noescape 118 func memequal(a, b unsafe.Pointer, size uintptr) bool 119 120 // noescape hides a pointer from escape analysis. noescape is 121 // the identity function but escape analysis doesn't think the 122 // output depends on the input. noescape is inlined and currently 123 // compiles down to zero instructions. 124 // USE CAREFULLY! 125 //go:nosplit 126 func noescape(p unsafe.Pointer) unsafe.Pointer { 127 x := uintptr(p) 128 return unsafe.Pointer(x ^ 0) 129 } 130 131 func cgocallback(fn, frame unsafe.Pointer, framesize, ctxt uintptr) 132 func gogo(buf *gobuf) 133 func gosave(buf *gobuf) 134 135 //go:noescape 136 func jmpdefer(fv *funcval, argp uintptr) 137 func exit1(code int32) 138 func asminit() 139 func setg(gg *g) 140 func breakpoint() 141 142 // reflectcall calls fn with a copy of the n argument bytes pointed at by arg. 143 // After fn returns, reflectcall copies n-retoffset result bytes 144 // back into arg+retoffset before returning. If copying result bytes back, 145 // the caller should pass the argument frame type as argtype, so that 146 // call can execute appropriate write barriers during the copy. 147 // Package reflect passes a frame type. In package runtime, there is only 148 // one call that copies results back, in cgocallbackg1, and it does NOT pass a 149 // frame type, meaning there are no write barriers invoked. See that call 150 // site for justification. 151 func reflectcall(argtype *_type, fn, arg unsafe.Pointer, argsize uint32, retoffset uint32) 152 153 func procyield(cycles uint32) 154 155 type neverCallThisFunction struct{} 156 157 // goexit is the return stub at the top of every goroutine call stack. 158 // Each goroutine stack is constructed as if goexit called the 159 // goroutine's entry point function, so that when the entry point 160 // function returns, it will return to goexit, which will call goexit1 161 // to perform the actual exit. 162 // 163 // This function must never be called directly. Call goexit1 instead. 164 // gentraceback assumes that goexit terminates the stack. A direct 165 // call on the stack will cause gentraceback to stop walking the stack 166 // prematurely and if there is leftover state it may panic. 167 func goexit(neverCallThisFunction) 168 169 // Not all cgocallback_gofunc frames are actually cgocallback_gofunc, 170 // so not all have these arguments. Mark them uintptr so that the GC 171 // does not misinterpret memory when the arguments are not present. 172 // cgocallback_gofunc is not called from go, only from cgocallback, 173 // so the arguments will be found via cgocallback's pointer-declared arguments. 174 // See the assembly implementations for more details. 175 func cgocallback_gofunc(fv uintptr, frame uintptr, framesize, ctxt uintptr) 176 177 // publicationBarrier performs a store/store barrier (a "publication" 178 // or "export" barrier). Some form of synchronization is required 179 // between initializing an object and making that object accessible to 180 // another processor. Without synchronization, the initialization 181 // writes and the "publication" write may be reordered, allowing the 182 // other processor to follow the pointer and observe an uninitialized 183 // object. In general, higher-level synchronization should be used, 184 // such as locking or an atomic pointer write. publicationBarrier is 185 // for when those aren't an option, such as in the implementation of 186 // the memory manager. 187 // 188 // There's no corresponding barrier for the read side because the read 189 // side naturally has a data dependency order. All architectures that 190 // Go supports or seems likely to ever support automatically enforce 191 // data dependency ordering. 192 func publicationBarrier() 193 194 // getcallerpc returns the program counter (PC) of its caller's caller. 195 // getcallersp returns the stack pointer (SP) of its caller's caller. 196 // For both, the argp must be a pointer to the caller's first function argument. 197 // The implementation may or may not use argp, depending on 198 // the architecture. 199 // 200 // For example: 201 // 202 // func f(arg1, arg2, arg3 int) { 203 // pc := getcallerpc(unsafe.Pointer(&arg1)) 204 // sp := getcallersp(unsafe.Pointer(&arg1)) 205 // } 206 // 207 // These two lines find the PC and SP immediately following 208 // the call to f (where f will return). 209 // 210 // The call to getcallerpc and getcallersp must be done in the 211 // frame being asked about. It would not be correct for f to pass &arg1 212 // to another function g and let g call getcallerpc/getcallersp. 213 // The call inside g might return information about g's caller or 214 // information about f's caller or complete garbage. 215 // 216 // The result of getcallersp is correct at the time of the return, 217 // but it may be invalidated by any subsequent call to a function 218 // that might relocate the stack in order to grow or shrink it. 219 // A general rule is that the result of getcallersp should be used 220 // immediately and can only be passed to nosplit functions. 221 222 //go:noescape 223 func getcallerpc(argp unsafe.Pointer) uintptr 224 225 //go:nosplit 226 func getcallersp(argp unsafe.Pointer) uintptr { 227 return uintptr(argp) - sys.MinFrameSize 228 } 229 230 // getclosureptr returns the pointer to the current closure. 231 // getclosureptr can only be used in an assignment statement 232 // at the entry of a function. Moreover, go:nosplit directive 233 // must be specified at the declaration of caller function, 234 // so that the function prolog does not clobber the closure register. 235 // for example: 236 // 237 // //go:nosplit 238 // func f(arg1, arg2, arg3 int) { 239 // dx := getclosureptr() 240 // } 241 // 242 // The compiler rewrites calls to this function into instructions that fetch the 243 // pointer from a well-known register (DX on x86 architecture, etc.) directly. 244 func getclosureptr() uintptr 245 246 //go:noescape 247 func asmcgocall(fn, arg unsafe.Pointer) int32 248 249 // argp used in Defer structs when there is no argp. 250 const _NoArgs = ^uintptr(0) 251 252 func morestack() 253 func morestack_noctxt() 254 func rt0_go() 255 256 // return0 is a stub used to return 0 from deferproc. 257 // It is called at the very end of deferproc to signal 258 // the calling Go function that it should not jump 259 // to deferreturn. 260 // in asm_*.s 261 func return0() 262 263 // in asm_*.s 264 // not called directly; definitions here supply type information for traceback. 265 func call32(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 266 func call64(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 267 func call128(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 268 func call256(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 269 func call512(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 270 func call1024(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 271 func call2048(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 272 func call4096(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 273 func call8192(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 274 func call16384(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 275 func call32768(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 276 func call65536(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 277 func call131072(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 278 func call262144(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 279 func call524288(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 280 func call1048576(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 281 func call2097152(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 282 func call4194304(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 283 func call8388608(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 284 func call16777216(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 285 func call33554432(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 286 func call67108864(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 287 func call134217728(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 288 func call268435456(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 289 func call536870912(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 290 func call1073741824(typ, fn, arg unsafe.Pointer, n, retoffset uint32) 291 292 func systemstack_switch() 293 294 // round n up to a multiple of a. a must be a power of 2. 295 func round(n, a uintptr) uintptr { 296 return (n + a - 1) &^ (a - 1) 297 } 298 299 // checkASM returns whether assembly runtime checks have passed. 300 func checkASM() bool 301 302 func memequal_varlen(a, b unsafe.Pointer) bool 303 func eqstring(s1, s2 string) bool 304 305 // bool2int returns 0 if x is false or 1 if x is true. 306 func bool2int(x bool) int { 307 // Avoid branches. In the SSA compiler, this compiles to 308 // exactly what you would want it to. 309 return int(uint8(*(*uint8)(unsafe.Pointer(&x)))) 310 }