Source file src/runtime/cgocall.go
1 // Copyright 2009 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 // Cgo call and callback support. 6 // 7 // To call into the C function f from Go, the cgo-generated code calls 8 // runtime.cgocall(_cgo_Cfunc_f, frame), where _cgo_Cfunc_f is a 9 // gcc-compiled function written by cgo. 10 // 11 // runtime.cgocall (below) calls entersyscall so as not to block 12 // other goroutines or the garbage collector, and then calls 13 // runtime.asmcgocall(_cgo_Cfunc_f, frame). 14 // 15 // runtime.asmcgocall (in asm_$GOARCH.s) switches to the m->g0 stack 16 // (assumed to be an operating system-allocated stack, so safe to run 17 // gcc-compiled code on) and calls _cgo_Cfunc_f(frame). 18 // 19 // _cgo_Cfunc_f invokes the actual C function f with arguments 20 // taken from the frame structure, records the results in the frame, 21 // and returns to runtime.asmcgocall. 22 // 23 // After it regains control, runtime.asmcgocall switches back to the 24 // original g (m->curg)'s stack and returns to runtime.cgocall. 25 // 26 // After it regains control, runtime.cgocall calls exitsyscall, which blocks 27 // until this m can run Go code without violating the $GOMAXPROCS limit, 28 // and then unlocks g from m. 29 // 30 // The above description skipped over the possibility of the gcc-compiled 31 // function f calling back into Go. If that happens, we continue down 32 // the rabbit hole during the execution of f. 33 // 34 // To make it possible for gcc-compiled C code to call a Go function p.GoF, 35 // cgo writes a gcc-compiled function named GoF (not p.GoF, since gcc doesn't 36 // know about packages). The gcc-compiled C function f calls GoF. 37 // 38 // GoF initializes "frame", a structure containing all of its 39 // arguments and slots for p.GoF's results. It calls 40 // crosscall2(_cgoexp_GoF, frame, framesize, ctxt) using the gcc ABI. 41 // 42 // crosscall2 (in cgo/asm_$GOARCH.s) is a four-argument adapter from 43 // the gcc function call ABI to the gc function call ABI. At this 44 // point we're in the Go runtime, but we're still running on m.g0's 45 // stack and outside the $GOMAXPROCS limit. crosscall2 calls 46 // runtime.cgocallback(_cgoexp_GoF, frame, ctxt) using the gc ABI. 47 // (crosscall2's framesize argument is no longer used, but there's one 48 // case where SWIG calls crosscall2 directly and expects to pass this 49 // argument. See _cgo_panic.) 50 // 51 // runtime.cgocallback (in asm_$GOARCH.s) switches from m.g0's stack 52 // to the original g (m.curg)'s stack, on which it calls 53 // runtime.cgocallbackg(_cgoexp_GoF, frame, ctxt). As part of the 54 // stack switch, runtime.cgocallback saves the current SP as 55 // m.g0.sched.sp, so that any use of m.g0's stack during the execution 56 // of the callback will be done below the existing stack frames. 57 // Before overwriting m.g0.sched.sp, it pushes the old value on the 58 // m.g0 stack, so that it can be restored later. 59 // 60 // runtime.cgocallbackg (below) is now running on a real goroutine 61 // stack (not an m.g0 stack). First it calls runtime.exitsyscall, which will 62 // block until the $GOMAXPROCS limit allows running this goroutine. 63 // Once exitsyscall has returned, it is safe to do things like call the memory 64 // allocator or invoke the Go callback function. runtime.cgocallbackg 65 // first defers a function to unwind m.g0.sched.sp, so that if p.GoF 66 // panics, m.g0.sched.sp will be restored to its old value: the m.g0 stack 67 // and the m.curg stack will be unwound in lock step. 68 // Then it calls _cgoexp_GoF(frame). 69 // 70 // _cgoexp_GoF, which was generated by cmd/cgo, unpacks the arguments 71 // from frame, calls p.GoF, writes the results back to frame, and 72 // returns. Now we start unwinding this whole process. 73 // 74 // runtime.cgocallbackg pops but does not execute the deferred 75 // function to unwind m.g0.sched.sp, calls runtime.entersyscall, and 76 // returns to runtime.cgocallback. 77 // 78 // After it regains control, runtime.cgocallback switches back to 79 // m.g0's stack (the pointer is still in m.g0.sched.sp), restores the old 80 // m.g0.sched.sp value from the stack, and returns to crosscall2. 81 // 82 // crosscall2 restores the callee-save registers for gcc and returns 83 // to GoF, which unpacks any result values and returns to f. 84 85 package runtime 86 87 import ( 88 "internal/abi" 89 "internal/goarch" 90 "internal/goexperiment" 91 "internal/runtime/sys" 92 "unsafe" 93 ) 94 95 // Addresses collected in a cgo backtrace when crashing. 96 // Length must match arg.Max in x_cgo_callers in runtime/cgo/gcc_traceback.c. 97 type cgoCallers [32]uintptr 98 99 // argset matches runtime/cgo/linux_syscall.c:argset_t 100 type argset struct { 101 args unsafe.Pointer 102 retval uintptr 103 } 104 105 // wrapper for syscall package to call cgocall for libc (cgo) calls. 106 // 107 //go:linkname syscall_cgocaller syscall.cgocaller 108 //go:nosplit 109 //go:uintptrescapes 110 func syscall_cgocaller(fn unsafe.Pointer, args ...uintptr) uintptr { 111 as := argset{args: unsafe.Pointer(&args[0])} 112 cgocall(fn, unsafe.Pointer(&as)) 113 return as.retval 114 } 115 116 var ncgocall uint64 // number of cgo calls in total for dead m 117 118 // Call from Go to C. 119 // 120 // This must be nosplit because it's used for syscalls on some 121 // platforms. Syscalls may have untyped arguments on the stack, so 122 // it's not safe to grow or scan the stack. 123 // 124 // cgocall should be an internal detail, 125 // but widely used packages access it using linkname. 126 // Notable members of the hall of shame include: 127 // - github.com/ebitengine/purego 128 // 129 // Do not remove or change the type signature. 130 // See go.dev/issue/67401. 131 // 132 //go:linkname cgocall 133 //go:nosplit 134 func cgocall(fn, arg unsafe.Pointer) int32 { 135 if !iscgo && GOOS != "solaris" && GOOS != "illumos" && GOOS != "windows" { 136 throw("cgocall unavailable") 137 } 138 139 if fn == nil { 140 throw("cgocall nil") 141 } 142 143 if raceenabled { 144 racereleasemerge(unsafe.Pointer(&racecgosync)) 145 } 146 147 mp := getg().m 148 mp.ncgocall++ 149 150 // Reset traceback. 151 mp.cgoCallers[0] = 0 152 153 // Announce we are entering a system call 154 // so that the scheduler knows to create another 155 // M to run goroutines while we are in the 156 // foreign code. 157 // 158 // The call to asmcgocall is guaranteed not to 159 // grow the stack and does not allocate memory, 160 // so it is safe to call while "in a system call", outside 161 // the $GOMAXPROCS accounting. 162 // 163 // fn may call back into Go code, in which case we'll exit the 164 // "system call", run the Go code (which may grow the stack), 165 // and then re-enter the "system call" reusing the PC and SP 166 // saved by entersyscall here. 167 entersyscall() 168 169 mp.incgo = true 170 // We use ncgo as a check during execution tracing for whether there is 171 // any C on the call stack, which there will be after this point. If 172 // there isn't, we can use frame pointer unwinding to collect call 173 // stacks efficiently. This will be the case for the first Go-to-C call 174 // on a stack, so it's preferable to update it here, after we emit a 175 // trace event in entersyscall above. 176 mp.ncgo++ 177 178 errno := asmcgocall(fn, arg) 179 180 // Update accounting before exitsyscall because exitsyscall may 181 // reschedule us on to a different M. 182 mp.incgo = false 183 mp.ncgo-- 184 185 // After exitsyscall we can be rescheduled on a different M, 186 // so we need to restore the original M's winsyscall. 187 winsyscall := mp.winsyscall 188 189 exitsyscall() 190 191 getg().m.winsyscall = winsyscall 192 193 // Note that raceacquire must be called only after exitsyscall has 194 // wired this M to a P. 195 if raceenabled { 196 raceacquire(unsafe.Pointer(&racecgosync)) 197 } 198 199 if sys.DITSupported { 200 // C code may have enabled or disabled DIT on this thread, restore 201 // our state to the expected one. 202 ditEnabled := sys.DITEnabled() 203 gp := getg() 204 if !gp.ditWanted && ditEnabled { 205 sys.DisableDIT() 206 } else if gp.ditWanted && !ditEnabled { 207 sys.EnableDIT() 208 } 209 } 210 211 // From the garbage collector's perspective, time can move 212 // backwards in the sequence above. If there's a callback into 213 // Go code, GC will see this function at the call to 214 // asmcgocall. When the Go call later returns to C, the 215 // syscall PC/SP is rolled back and the GC sees this function 216 // back at the call to entersyscall. Normally, fn and arg 217 // would be live at entersyscall and dead at asmcgocall, so if 218 // time moved backwards, GC would see these arguments as dead 219 // and then live. Prevent these undead arguments from crashing 220 // GC by forcing them to stay live across this time warp. 221 KeepAlive(fn) 222 KeepAlive(arg) 223 KeepAlive(mp) 224 225 return errno 226 } 227 228 // Set or reset the system stack bounds for a callback on sp. 229 // 230 // Must be nosplit because it is called by needm prior to fully initializing 231 // the M. 232 // 233 //go:nosplit 234 func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) { 235 g0 := mp.g0 236 237 if !mp.isextra { 238 // We allocated the stack for standard Ms. Don't replace the 239 // stack bounds with estimated ones when we already initialized 240 // with the exact ones. 241 return 242 } 243 244 inBound := sp > g0.stack.lo && sp <= g0.stack.hi 245 if inBound && mp.g0StackAccurate { 246 // This M has called into Go before and has the stack bounds 247 // initialized. We have the accurate stack bounds, and the SP 248 // is in bounds. We expect it continues to run within the same 249 // bounds. 250 return 251 } 252 253 // We don't have an accurate stack bounds (either it never calls 254 // into Go before, or we couldn't get the accurate bounds), or the 255 // current SP is not within the previous bounds (the stack may have 256 // changed between calls). We need to update the stack bounds. 257 // 258 // N.B. we need to update the stack bounds even if SP appears to 259 // already be in bounds, if our bounds are estimated dummy bounds 260 // (below). We may be in a different region within the same actual 261 // stack bounds, but our estimates were not accurate. Or the actual 262 // stack bounds could have shifted but still have partial overlap with 263 // our dummy bounds. If we failed to update in that case, we could find 264 // ourselves seemingly called near the bottom of the stack bounds, where 265 // we quickly run out of space. 266 267 // Set the stack bounds to match the current stack. If we don't 268 // actually know how big the stack is, like we don't know how big any 269 // scheduling stack is, but we assume there's at least 32 kB. If we 270 // can get a more accurate stack bound from pthread, use that, provided 271 // it actually contains SP. 272 g0.stack.hi = sp + 1024 273 g0.stack.lo = sp - 32*1024 274 mp.g0StackAccurate = false 275 if !signal && _cgo_getstackbound != nil { 276 // Don't adjust if called from the signal handler. 277 // We are on the signal stack, not the pthread stack. 278 // (We could get the stack bounds from sigaltstack, but 279 // we're getting out of the signal handler very soon 280 // anyway. Not worth it.) 281 var bounds [2]uintptr 282 asmcgocall(_cgo_getstackbound, unsafe.Pointer(&bounds)) 283 // getstackbound is an unsupported no-op on Windows. 284 // 285 // On Unix systems, if the API to get accurate stack bounds is 286 // not available, it returns zeros. 287 // 288 // Don't use these bounds if they don't contain SP. Perhaps we 289 // were called by something not using the standard thread 290 // stack. 291 if bounds[0] != 0 && sp > bounds[0] && sp <= bounds[1] { 292 g0.stack.lo = bounds[0] 293 g0.stack.hi = bounds[1] 294 mp.g0StackAccurate = true 295 } 296 } 297 g0.stackguard0 = g0.stack.lo + stackGuard 298 g0.stackguard1 = g0.stackguard0 299 } 300 301 // Call from C back to Go. fn must point to an ABIInternal Go entry-point. 302 // 303 //go:nosplit 304 func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) { 305 gp := getg() 306 if gp != gp.m.curg { 307 println("runtime: bad g in cgocallback") 308 exit(2) 309 } 310 311 sp := gp.m.g0.sched.sp // system sp saved by cgocallback. 312 oldStack := gp.m.g0.stack 313 oldAccurate := gp.m.g0StackAccurate 314 callbackUpdateSystemStack(gp.m, sp, false) 315 316 // The call from C is on gp.m's g0 stack, so we must ensure 317 // that we stay on that M. We have to do this before calling 318 // exitsyscall, since it would otherwise be free to move us to 319 // a different M. The call to unlockOSThread is in this function 320 // after cgocallbackg1, or in the case of panicking, in unwindm. 321 lockOSThread() 322 323 checkm := gp.m 324 325 // Save current syscall parameters, so m.winsyscall can be 326 // used again if callback decide to make syscall. 327 winsyscall := gp.m.winsyscall 328 329 // entersyscall saves the caller's SP to allow the GC to trace the Go 330 // stack. However, since we're returning to an earlier stack frame and 331 // need to pair with the entersyscall() call made by cgocall, we must 332 // save syscall* and let reentersyscall restore them. 333 // 334 // Note: savedsp and savedbp MUST be held in locals as an unsafe.Pointer. 335 // When we call into Go, the stack is free to be moved. If these locals 336 // aren't visible in the stack maps, they won't get updated properly, 337 // and will end up being stale when restored by reentersyscall. 338 savedsp := unsafe.Pointer(gp.syscallsp) 339 savedpc := gp.syscallpc 340 savedbp := unsafe.Pointer(gp.syscallbp) 341 exitsyscall() // coming out of cgo call 342 gp.m.incgo = false 343 if gp.m.isextra { 344 gp.m.isExtraInC = false 345 } 346 347 if gp.nocgocallback { 348 panic("runtime: function marked with #cgo nocallback called back into Go") 349 } 350 351 cgocallbackg1(fn, frame, ctxt) 352 353 // At this point we're about to call unlockOSThread. 354 // The following code must not change to a different m. 355 // This is enforced by checking incgo in the schedule function. 356 gp.m.incgo = true 357 unlockOSThread() 358 359 if gp.m.isextra && gp.m.ncgo == 0 { 360 // There are no active cgocalls above this frame (ncgo == 0), 361 // thus there can't be more Go frames above this frame. 362 gp.m.isExtraInC = true 363 } 364 365 if gp.m != checkm { 366 throw("m changed unexpectedly in cgocallbackg") 367 } 368 369 // going back to cgo call 370 reentersyscall(savedpc, uintptr(savedsp), uintptr(savedbp)) 371 372 gp.m.winsyscall = winsyscall 373 374 // Restore the old g0 stack bounds 375 gp.m.g0.stack = oldStack 376 gp.m.g0.stackguard0 = oldStack.lo + stackGuard 377 gp.m.g0.stackguard1 = gp.m.g0.stackguard0 378 gp.m.g0StackAccurate = oldAccurate 379 } 380 381 func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) { 382 gp := getg() 383 384 if gp.m.needextram || extraMWaiters.Load() > 0 { 385 gp.m.needextram = false 386 systemstack(newextram) 387 } 388 389 if ctxt != 0 { 390 s := append(gp.cgoCtxt, ctxt) 391 392 // Now we need to set gp.cgoCtxt = s, but we could get 393 // a SIGPROF signal while manipulating the slice, and 394 // the SIGPROF handler could pick up gp.cgoCtxt while 395 // tracing up the stack. We need to ensure that the 396 // handler always sees a valid slice, so set the 397 // values in an order such that it always does. 398 p := (*slice)(unsafe.Pointer(&gp.cgoCtxt)) 399 atomicstorep(unsafe.Pointer(&p.array), unsafe.Pointer(&s[0])) 400 p.cap = cap(s) 401 p.len = len(s) 402 403 defer func(gp *g) { 404 // Decrease the length of the slice by one, safely. 405 p := (*slice)(unsafe.Pointer(&gp.cgoCtxt)) 406 p.len-- 407 }(gp) 408 } 409 410 if gp.m.ncgo == 0 { 411 // The C call to Go came from a thread not currently running 412 // any Go. In the case of -buildmode=c-archive or c-shared, 413 // this call may be coming in before package initialization 414 // is complete. Don't proceed until it is. 415 // 416 // We check a bool first for speed, and wait on a channel 417 // if it's not ready. 418 // 419 // In race mode, skip the optimization and always use the 420 // channel, which has the race instrumentation. 421 if raceenabled || !mainInitDone.Load() { 422 <-mainInitDoneChan 423 } 424 } 425 426 // Check whether the profiler needs to be turned on or off; this route to 427 // run Go code does not use runtime.execute, so bypasses the check there. 428 hz := sched.profilehz 429 if gp.m.profilehz != hz { 430 setThreadCPUProfiler(hz) 431 } 432 433 // Add entry to defer stack in case of panic. 434 restore := true 435 defer unwindm(&restore) 436 437 var ditStateM, ditStateG bool 438 if debug.dataindependenttiming == 1 && gp.m.isextra { 439 // We only need to enable DIT for threads that were created by C, as it 440 // should already by enabled on threads that were created by Go. 441 ditStateM = sys.EnableDIT() 442 } else if sys.DITSupported && debug.dataindependenttiming != 1 { 443 // C code may have enabled or disabled DIT on this thread. Set the flag 444 // on the M and G accordingly, saving their previous state to restore 445 // on return from the callback. 446 ditStateM, ditStateG = gp.m.ditEnabled, gp.ditWanted 447 ditEnabled := sys.DITEnabled() 448 gp.ditWanted = ditEnabled 449 gp.m.ditEnabled = ditEnabled 450 } 451 452 if raceenabled { 453 raceacquire(unsafe.Pointer(&racecgosync)) 454 } 455 456 // Invoke callback. This function is generated by cmd/cgo and 457 // will unpack the argument frame and call the Go function. 458 var cb func(frame unsafe.Pointer) 459 cbFV := funcval{uintptr(fn)} 460 *(*unsafe.Pointer)(unsafe.Pointer(&cb)) = noescape(unsafe.Pointer(&cbFV)) 461 cb(frame) 462 463 if raceenabled { 464 racereleasemerge(unsafe.Pointer(&racecgosync)) 465 } 466 467 if debug.dataindependenttiming == 1 && !ditStateM { 468 // Only unset DIT if it wasn't already enabled when cgocallback was called. 469 sys.DisableDIT() 470 } else if sys.DITSupported && debug.dataindependenttiming != 1 { 471 // Restore DIT state on M and G. 472 gp.ditWanted = ditStateG 473 gp.m.ditEnabled = ditStateM 474 if !ditStateM { 475 sys.DisableDIT() 476 } 477 } 478 479 // Do not unwind m->g0->sched.sp. 480 // Our caller, cgocallback, will do that. 481 restore = false 482 } 483 484 func unwindm(restore *bool) { 485 if *restore { 486 // Restore sp saved by cgocallback during 487 // unwind of g's stack (see comment at top of file). 488 mp := acquirem() 489 sched := &mp.g0.sched 490 sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + alignUp(sys.MinFrameSize, sys.StackAlign))) 491 492 // Do the accounting that cgocall will not have a chance to do 493 // during an unwind. 494 // 495 // In the case where a Go call originates from C, ncgo is 0 496 // and there is no matching cgocall to end. 497 if mp.ncgo > 0 { 498 mp.incgo = false 499 mp.ncgo-- 500 } 501 502 // Undo the call to lockOSThread in cgocallbackg, only on the 503 // panicking path. In normal return case cgocallbackg will call 504 // unlockOSThread, ensuring no preemption point after the unlock. 505 // Here we don't need to worry about preemption, because we're 506 // panicking out of the callback and unwinding the g0 stack, 507 // instead of reentering cgo (which requires the same thread). 508 unlockOSThread() 509 510 releasem(mp) 511 } 512 } 513 514 // called from assembly. 515 func badcgocallback() { 516 throw("misaligned stack in cgocallback") 517 } 518 519 // called from (incomplete) assembly. 520 func cgounimpl() { 521 throw("cgo not implemented") 522 } 523 524 var racecgosync uint64 // represents possible synchronization in C code 525 526 // Pointer checking for cgo code. 527 528 // We want to detect all cases where a program that does not use 529 // unsafe makes a cgo call passing a Go pointer to memory that 530 // contains an unpinned Go pointer. Here a Go pointer is defined as a 531 // pointer to memory allocated by the Go runtime. Programs that use 532 // unsafe can evade this restriction easily, so we don't try to catch 533 // them. The cgo program will rewrite all possibly bad pointer 534 // arguments to call cgoCheckPointer, where we can catch cases of a Go 535 // pointer pointing to an unpinned Go pointer. 536 537 // Complicating matters, taking the address of a slice or array 538 // element permits the C program to access all elements of the slice 539 // or array. In that case we will see a pointer to a single element, 540 // but we need to check the entire data structure. 541 542 // The cgoCheckPointer call takes additional arguments indicating that 543 // it was called on an address expression. An additional argument of 544 // true means that it only needs to check a single element. An 545 // additional argument of a slice or array means that it needs to 546 // check the entire slice/array, but nothing else. Otherwise, the 547 // pointer could be anything, and we check the entire heap object, 548 // which is conservative but safe. 549 550 // When and if we implement a moving garbage collector, 551 // cgoCheckPointer will pin the pointer for the duration of the cgo 552 // call. (This is necessary but not sufficient; the cgo program will 553 // also have to change to pin Go pointers that cannot point to Go 554 // pointers.) 555 556 // cgoCheckPointer checks if the argument contains a Go pointer that 557 // points to an unpinned Go pointer, and panics if it does. 558 func cgoCheckPointer(ptr any, arg any) { 559 if !goexperiment.CgoCheck2 && debug.cgocheck == 0 { 560 return 561 } 562 563 ep := efaceOf(&ptr) 564 t := ep._type 565 566 top := true 567 if arg != nil && (t.Kind() == abi.Pointer || t.Kind() == abi.UnsafePointer) { 568 p := ep.data 569 if !t.IsDirectIface() { 570 p = *(*unsafe.Pointer)(p) 571 } 572 if p == nil || !cgoIsGoPointer(p) { 573 return 574 } 575 aep := efaceOf(&arg) 576 switch aep._type.Kind() { 577 case abi.Bool: 578 if t.Kind() == abi.UnsafePointer { 579 // We don't know the type of the element. 580 break 581 } 582 pt := (*ptrtype)(unsafe.Pointer(t)) 583 cgoCheckArg(pt.Elem, p, true, false, cgoCheckPointerFail) 584 return 585 case abi.Slice: 586 // Check the slice rather than the pointer. 587 ep = aep 588 t = ep._type 589 case abi.Array: 590 // Check the array rather than the pointer. 591 // Pass top as false since we have a pointer 592 // to the array. 593 ep = aep 594 t = ep._type 595 top = false 596 case abi.Pointer: 597 // The Go code is indexing into a pointer to an array, 598 // and we have been passed the pointer-to-array. 599 // Check the array rather than the pointer. 600 pt := (*abi.PtrType)(unsafe.Pointer(aep._type)) 601 t = pt.Elem 602 if t.Kind() != abi.Array { 603 throw("can't happen") 604 } 605 ep = aep 606 top = false 607 default: 608 throw("can't happen") 609 } 610 } 611 612 cgoCheckArg(t, ep.data, !t.IsDirectIface(), top, cgoCheckPointerFail) 613 } 614 615 type cgoErrorMsg int 616 617 const ( 618 cgoCheckPointerFail cgoErrorMsg = iota 619 cgoResultFail 620 ) 621 622 // cgoCheckArg is the real work of cgoCheckPointer and cgoCheckResult. 623 // The argument p is either a pointer to the value (of type t), or the value 624 // itself, depending on indir. The top parameter is whether we are at the top 625 // level, where Go pointers are allowed. Go pointers to pinned objects are 626 // allowed as long as they don't reference other unpinned pointers. 627 func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg cgoErrorMsg) { 628 if !t.Pointers() || p == nil { 629 // If the type has no pointers there is nothing to do. 630 return 631 } 632 633 switch t.Kind() { 634 default: 635 throw("can't happen") 636 case abi.Array: 637 at := (*arraytype)(unsafe.Pointer(t)) 638 if !indir { 639 if at.Len != 1 { 640 throw("can't happen") 641 } 642 cgoCheckArg(at.Elem, p, !at.Elem.IsDirectIface(), top, msg) 643 return 644 } 645 for i := uintptr(0); i < at.Len; i++ { 646 cgoCheckArg(at.Elem, p, true, top, msg) 647 p = add(p, at.Elem.Size_) 648 } 649 case abi.Chan, abi.Map: 650 // These types contain internal pointers that will 651 // always be allocated in the Go heap. It's never OK 652 // to pass them to C. 653 panic(cgoFormatErr(msg, t.Kind())) 654 case abi.Func: 655 if indir { 656 p = *(*unsafe.Pointer)(p) 657 } 658 if !cgoIsGoPointer(p) { 659 return 660 } 661 panic(cgoFormatErr(msg, t.Kind())) 662 case abi.Interface: 663 it := *(**_type)(p) 664 if it == nil { 665 return 666 } 667 // A type known at compile time is OK since it's 668 // constant. A type not known at compile time will be 669 // in the heap and will not be OK. 670 if inheap(uintptr(unsafe.Pointer(it))) { 671 panic(cgoFormatErr(msg, t.Kind())) 672 } 673 p = *(*unsafe.Pointer)(add(p, goarch.PtrSize)) 674 if !cgoIsGoPointer(p) { 675 return 676 } 677 if !top && !isPinned(p) { 678 panic(cgoFormatErr(msg, t.Kind())) 679 } 680 cgoCheckArg(it, p, !it.IsDirectIface(), false, msg) 681 case abi.Slice: 682 st := (*slicetype)(unsafe.Pointer(t)) 683 s := (*slice)(p) 684 p = s.array 685 if p == nil || !cgoIsGoPointer(p) { 686 return 687 } 688 if !top && !isPinned(p) { 689 panic(cgoFormatErr(msg, t.Kind())) 690 } 691 if !st.Elem.Pointers() { 692 return 693 } 694 for i := 0; i < s.cap; i++ { 695 cgoCheckArg(st.Elem, p, true, false, msg) 696 p = add(p, st.Elem.Size_) 697 } 698 case abi.String: 699 ss := (*stringStruct)(p) 700 if !cgoIsGoPointer(ss.str) { 701 return 702 } 703 if !top && !isPinned(ss.str) { 704 panic(cgoFormatErr(msg, t.Kind())) 705 } 706 case abi.Struct: 707 st := (*structtype)(unsafe.Pointer(t)) 708 if !indir { 709 if len(st.Fields) != 1 { 710 throw("can't happen") 711 } 712 cgoCheckArg(st.Fields[0].Typ, p, !st.Fields[0].Typ.IsDirectIface(), top, msg) 713 return 714 } 715 for _, f := range st.Fields { 716 if !f.Typ.Pointers() { 717 continue 718 } 719 cgoCheckArg(f.Typ, add(p, f.Offset), true, top, msg) 720 } 721 case abi.Pointer, abi.UnsafePointer: 722 if indir { 723 p = *(*unsafe.Pointer)(p) 724 if p == nil { 725 return 726 } 727 } 728 729 if !cgoIsGoPointer(p) { 730 return 731 } 732 if !top && !isPinned(p) { 733 panic(cgoFormatErr(msg, t.Kind())) 734 } 735 736 cgoCheckUnknownPointer(p, msg) 737 } 738 } 739 740 // cgoCheckUnknownPointer is called for an arbitrary pointer into Go 741 // memory. It checks whether that Go memory contains any other 742 // pointer into unpinned Go memory. If it does, we panic. 743 // The return values are unused but useful to see in panic tracebacks. 744 func cgoCheckUnknownPointer(p unsafe.Pointer, msg cgoErrorMsg) (base, i uintptr) { 745 if inheap(uintptr(p)) { 746 b, span, _ := findObject(uintptr(p), 0, 0) 747 base = b 748 if base == 0 { 749 return 750 } 751 tp := span.typePointersOfUnchecked(base) 752 for { 753 var addr uintptr 754 if tp, addr = tp.next(base + span.elemsize); addr == 0 { 755 break 756 } 757 pp := *(*unsafe.Pointer)(unsafe.Pointer(addr)) 758 if cgoIsGoPointer(pp) && !isPinned(pp) { 759 panic(cgoFormatErr(msg, abi.Pointer)) 760 } 761 } 762 return 763 } 764 765 for _, datap := range activeModules() { 766 if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) { 767 // We have no way to know the size of the object. 768 // We have to assume that it might contain a pointer. 769 panic(cgoFormatErr(msg, abi.Pointer)) 770 } 771 // In the text or noptr sections, we know that the 772 // pointer does not point to a Go pointer. 773 } 774 775 return 776 } 777 778 // cgoIsGoPointer reports whether the pointer is a Go pointer--a 779 // pointer to Go memory. We only care about Go memory that might 780 // contain pointers. 781 // 782 //go:nosplit 783 //go:nowritebarrierrec 784 func cgoIsGoPointer(p unsafe.Pointer) bool { 785 if p == nil { 786 return false 787 } 788 789 if inHeapOrStack(uintptr(p)) { 790 return true 791 } 792 793 for _, datap := range activeModules() { 794 if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) { 795 return true 796 } 797 } 798 799 return false 800 } 801 802 // cgoInRange reports whether p is between start and end. 803 // 804 //go:nosplit 805 //go:nowritebarrierrec 806 func cgoInRange(p unsafe.Pointer, start, end uintptr) bool { 807 return start <= uintptr(p) && uintptr(p) < end 808 } 809 810 // cgoCheckResult is called to check the result parameter of an 811 // exported Go function. It panics if the result is or contains any 812 // other pointer into unpinned Go memory. 813 func cgoCheckResult(val any) { 814 if !goexperiment.CgoCheck2 && debug.cgocheck == 0 { 815 return 816 } 817 818 ep := efaceOf(&val) 819 t := ep._type 820 if t == nil { 821 return 822 } 823 cgoCheckArg(t, ep.data, !t.IsDirectIface(), false, cgoResultFail) 824 } 825 826 // cgoFormatErr is called by cgoCheckArg and cgoCheckUnknownPointer 827 // to format panic error messages. 828 func cgoFormatErr(error cgoErrorMsg, kind abi.Kind) errorString { 829 var msg, kindname string 830 var cgoFunction string = "unknown" 831 var offset int 832 var buf [20]byte 833 834 // We expect one of these abi.Kind from cgoCheckArg 835 switch kind { 836 case abi.Chan: 837 kindname = "channel" 838 case abi.Func: 839 kindname = "function" 840 case abi.Interface: 841 kindname = "interface" 842 case abi.Map: 843 kindname = "map" 844 case abi.Pointer: 845 kindname = "pointer" 846 case abi.Slice: 847 kindname = "slice" 848 case abi.String: 849 kindname = "string" 850 case abi.Struct: 851 kindname = "struct" 852 case abi.UnsafePointer: 853 kindname = "unsafe pointer" 854 default: 855 kindname = "pointer" 856 } 857 858 // The cgo function name might need an offset to be obtained 859 if error == cgoResultFail { 860 offset = 21 861 } 862 863 // Relatively to cgoFormatErr, this is the stack frame: 864 // 0. cgoFormatErr 865 // 1. cgoCheckArg or cgoCheckUnknownPointer 866 // 2. cgoCheckPointer or cgoCheckResult 867 // 3. cgo function 868 pc, path, line, ok := Caller(3) 869 if ok && error == cgoResultFail { 870 function := FuncForPC(pc) 871 872 if function != nil { 873 // Expected format of cgo function name: 874 // - caller: _cgoexp_3c910ddb72c4_foo 875 if offset > len(function.Name()) { 876 cgoFunction = function.Name() 877 } else { 878 cgoFunction = function.Name()[offset:] 879 } 880 } 881 } 882 883 switch error { 884 case cgoResultFail: 885 msg = path + ":" + string(itoa(buf[:], uint64(line))) 886 msg += ": result of Go function " + cgoFunction + " called from cgo" 887 msg += " is unpinned Go " + kindname + " or points to unpinned Go " + kindname 888 case cgoCheckPointerFail: 889 msg += "argument of cgo function has Go pointer to unpinned Go " + kindname 890 } 891 892 return errorString(msg) 893 } 894