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 if GOOS == "windows" && mp.syncIOWorker && sched.npidle.Load() == 0 { 168 // Synchronous pipe I/O may need a peer goroutine to make progress. 169 // If no other P is idle, release ours now instead of waiting for 170 // sysmon to retake it. Otherwise, let a short call keep its P. 171 entersyscallblock() 172 } else { 173 entersyscall() 174 } 175 176 mp.incgo = true 177 // We use ncgo as a check during execution tracing for whether there is 178 // any C on the call stack, which there will be after this point. If 179 // there isn't, we can use frame pointer unwinding to collect call 180 // stacks efficiently. This will be the case for the first Go-to-C call 181 // on a stack, so it's preferable to update it here, after we emit a 182 // trace event in entersyscall above. 183 mp.ncgo++ 184 185 errno := asmcgocall(fn, arg) 186 187 // Update accounting before exitsyscall because exitsyscall may 188 // reschedule us on to a different M. 189 mp.incgo = false 190 mp.ncgo-- 191 192 // After exitsyscall we can be rescheduled on a different M, 193 // so we need to restore the original M's winsyscall. 194 winsyscall := mp.winsyscall 195 196 exitsyscall() 197 198 getg().m.winsyscall = winsyscall 199 200 // Note that raceacquire must be called only after exitsyscall has 201 // wired this M to a P. 202 if raceenabled { 203 raceacquire(unsafe.Pointer(&racecgosync)) 204 } 205 206 if sys.DITSupported { 207 // C code may have enabled or disabled DIT on this thread, restore 208 // our state to the expected one. 209 ditEnabled := sys.DITEnabled() 210 gp := getg() 211 if !gp.ditWanted && ditEnabled { 212 sys.DisableDIT() 213 } else if gp.ditWanted && !ditEnabled { 214 sys.EnableDIT() 215 } 216 } 217 218 // From the garbage collector's perspective, time can move 219 // backwards in the sequence above. If there's a callback into 220 // Go code, GC will see this function at the call to 221 // asmcgocall. When the Go call later returns to C, the 222 // syscall PC/SP is rolled back and the GC sees this function 223 // back at the call to entersyscall. Normally, fn and arg 224 // would be live at entersyscall and dead at asmcgocall, so if 225 // time moved backwards, GC would see these arguments as dead 226 // and then live. Prevent these undead arguments from crashing 227 // GC by forcing them to stay live across this time warp. 228 KeepAlive(fn) 229 KeepAlive(arg) 230 KeepAlive(mp) 231 232 return errno 233 } 234 235 // Set or reset the system stack bounds for a callback on sp. 236 // 237 // Must be nosplit because it is called by needm prior to fully initializing 238 // the M. 239 // 240 //go:nosplit 241 func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) { 242 g0 := mp.g0 243 244 if !mp.isextra { 245 // We allocated the stack for standard Ms. Don't replace the 246 // stack bounds with estimated ones when we already initialized 247 // with the exact ones. 248 return 249 } 250 251 inBound := sp > g0.stack.lo && sp <= g0.stack.hi 252 if inBound && mp.g0StackAccurate { 253 // This M has called into Go before and has the stack bounds 254 // initialized. We have the accurate stack bounds, and the SP 255 // is in bounds. We expect it continues to run within the same 256 // bounds. 257 return 258 } 259 260 // We don't have an accurate stack bounds (either it never calls 261 // into Go before, or we couldn't get the accurate bounds), or the 262 // current SP is not within the previous bounds (the stack may have 263 // changed between calls). We need to update the stack bounds. 264 // 265 // N.B. we need to update the stack bounds even if SP appears to 266 // already be in bounds, if our bounds are estimated dummy bounds 267 // (below). We may be in a different region within the same actual 268 // stack bounds, but our estimates were not accurate. Or the actual 269 // stack bounds could have shifted but still have partial overlap with 270 // our dummy bounds. If we failed to update in that case, we could find 271 // ourselves seemingly called near the bottom of the stack bounds, where 272 // we quickly run out of space. 273 274 // Set the stack bounds to match the current stack. If we don't 275 // actually know how big the stack is, like we don't know how big any 276 // scheduling stack is, but we assume there's at least 32 kB. If we 277 // can get a more accurate stack bound from pthread, use that, provided 278 // it actually contains SP. 279 g0.stack.hi = sp + 1024 280 g0.stack.lo = sp - 32*1024 281 mp.g0StackAccurate = false 282 if !signal && _cgo_getstackbound != nil { 283 // Don't adjust if called from the signal handler. 284 // We are on the signal stack, not the pthread stack. 285 // (We could get the stack bounds from sigaltstack, but 286 // we're getting out of the signal handler very soon 287 // anyway. Not worth it.) 288 var bounds [2]uintptr 289 asmcgocall(_cgo_getstackbound, unsafe.Pointer(&bounds)) 290 // getstackbound is an unsupported no-op on Windows. 291 // 292 // On Unix systems, if the API to get accurate stack bounds is 293 // not available, it returns zeros. 294 // 295 // Don't use these bounds if they don't contain SP. Perhaps we 296 // were called by something not using the standard thread 297 // stack. 298 if bounds[0] != 0 && sp > bounds[0] && sp <= bounds[1] { 299 g0.stack.lo = bounds[0] 300 g0.stack.hi = bounds[1] 301 mp.g0StackAccurate = true 302 } 303 } 304 g0.stackguard0 = g0.stack.lo + stackGuard 305 g0.stackguard1 = g0.stackguard0 306 } 307 308 // Call from C back to Go. fn must point to an ABIInternal Go entry-point. 309 // 310 //go:nosplit 311 func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) { 312 gp := getg() 313 if gp != gp.m.curg { 314 println("runtime: bad g in cgocallback") 315 exit(2) 316 } 317 318 sp := gp.m.g0.sched.sp // system sp saved by cgocallback. 319 oldStack := gp.m.g0.stack 320 oldAccurate := gp.m.g0StackAccurate 321 callbackUpdateSystemStack(gp.m, sp, false) 322 323 // The call from C is on gp.m's g0 stack, so we must ensure 324 // that we stay on that M. We have to do this before calling 325 // exitsyscall, since it would otherwise be free to move us to 326 // a different M. The call to unlockOSThread is in this function 327 // after cgocallbackg1, or in the case of panicking, in unwindm. 328 lockOSThread() 329 330 checkm := gp.m 331 332 // Save current syscall parameters, so m.winsyscall can be 333 // used again if callback decide to make syscall. 334 winsyscall := gp.m.winsyscall 335 336 // entersyscall saves the caller's SP to allow the GC to trace the Go 337 // stack. However, since we're returning to an earlier stack frame and 338 // need to pair with the entersyscall() call made by cgocall, we must 339 // save syscall* and let reentersyscall restore them. 340 // 341 // Note: savedsp and savedbp MUST be held in locals as an unsafe.Pointer. 342 // When we call into Go, the stack is free to be moved. If these locals 343 // aren't visible in the stack maps, they won't get updated properly, 344 // and will end up being stale when restored by reentersyscall. 345 savedsp := unsafe.Pointer(gp.syscallsp) 346 savedpc := gp.syscallpc 347 savedbp := unsafe.Pointer(gp.syscallbp) 348 exitsyscall() // coming out of cgo call 349 gp.m.incgo = false 350 if gp.m.isextra { 351 gp.m.isExtraInC = false 352 } 353 354 if gp.nocgocallback { 355 panic("runtime: function marked with #cgo nocallback called back into Go") 356 } 357 358 cgocallbackg1(fn, frame, ctxt) 359 360 // At this point we're about to call unlockOSThread. 361 // The following code must not change to a different m. 362 // This is enforced by checking incgo in the schedule function. 363 gp.m.incgo = true 364 unlockOSThread() 365 366 if gp.m.isextra && gp.m.ncgo == 0 { 367 // There are no active cgocalls above this frame (ncgo == 0), 368 // thus there can't be more Go frames above this frame. 369 gp.m.isExtraInC = true 370 } 371 372 if gp.m != checkm { 373 throw("m changed unexpectedly in cgocallbackg") 374 } 375 376 // going back to cgo call 377 reentersyscall(savedpc, uintptr(savedsp), uintptr(savedbp)) 378 379 gp.m.winsyscall = winsyscall 380 381 // Restore the old g0 stack bounds 382 gp.m.g0.stack = oldStack 383 gp.m.g0.stackguard0 = oldStack.lo + stackGuard 384 gp.m.g0.stackguard1 = gp.m.g0.stackguard0 385 gp.m.g0StackAccurate = oldAccurate 386 } 387 388 func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) { 389 gp := getg() 390 391 if gp.m.needextram || extraMWaiters.Load() > 0 { 392 gp.m.needextram = false 393 systemstack(newextram) 394 } 395 396 if ctxt != 0 { 397 s := append(gp.cgoCtxt, ctxt) 398 399 // Now we need to set gp.cgoCtxt = s, but we could get 400 // a SIGPROF signal while manipulating the slice, and 401 // the SIGPROF handler could pick up gp.cgoCtxt while 402 // tracing up the stack. We need to ensure that the 403 // handler always sees a valid slice, so set the 404 // values in an order such that it always does. 405 p := (*slice)(unsafe.Pointer(&gp.cgoCtxt)) 406 atomicstorep(unsafe.Pointer(&p.array), unsafe.Pointer(&s[0])) 407 p.cap = cap(s) 408 p.len = len(s) 409 410 defer func(gp *g) { 411 // Decrease the length of the slice by one, safely. 412 p := (*slice)(unsafe.Pointer(&gp.cgoCtxt)) 413 p.len-- 414 }(gp) 415 } 416 417 if gp.m.ncgo == 0 { 418 // The C call to Go came from a thread not currently running 419 // any Go. In the case of -buildmode=c-archive or c-shared, 420 // this call may be coming in before package initialization 421 // is complete. Don't proceed until it is. 422 // 423 // We check a bool first for speed, and wait on a channel 424 // if it's not ready. 425 // 426 // In race mode, skip the optimization and always use the 427 // channel, which has the race instrumentation. 428 if raceenabled || !mainInitDone.Load() { 429 <-mainInitDoneChan 430 } 431 } 432 433 // Check whether the profiler needs to be turned on or off; this route to 434 // run Go code does not use runtime.execute, so bypasses the check there. 435 hz := sched.profilehz 436 if gp.m.profilehz != hz { 437 setThreadCPUProfiler(hz) 438 } 439 440 // Add entry to defer stack in case of panic. 441 restore := true 442 defer unwindm(&restore) 443 444 var ditStateM, ditStateG bool 445 if debug.dataindependenttiming == 1 && gp.m.isextra { 446 // We only need to enable DIT for threads that were created by C, as it 447 // should already by enabled on threads that were created by Go. 448 ditStateM = sys.EnableDIT() 449 } else if sys.DITSupported && debug.dataindependenttiming != 1 { 450 // C code may have enabled or disabled DIT on this thread. Set the flag 451 // on the M and G accordingly, saving their previous state to restore 452 // on return from the callback. 453 ditStateM, ditStateG = gp.m.ditEnabled, gp.ditWanted 454 ditEnabled := sys.DITEnabled() 455 gp.ditWanted = ditEnabled 456 gp.m.ditEnabled = ditEnabled 457 } 458 459 if raceenabled { 460 raceacquire(unsafe.Pointer(&racecgosync)) 461 } 462 463 // Invoke callback. This function is generated by cmd/cgo and 464 // will unpack the argument frame and call the Go function. 465 var cb func(frame unsafe.Pointer) 466 cbFV := funcval{uintptr(fn)} 467 *(*unsafe.Pointer)(unsafe.Pointer(&cb)) = noescape(unsafe.Pointer(&cbFV)) 468 cb(frame) 469 470 if raceenabled { 471 racereleasemerge(unsafe.Pointer(&racecgosync)) 472 } 473 474 if debug.dataindependenttiming == 1 && !ditStateM { 475 // Only unset DIT if it wasn't already enabled when cgocallback was called. 476 sys.DisableDIT() 477 } else if sys.DITSupported && debug.dataindependenttiming != 1 { 478 // Restore DIT state on M and G. 479 gp.ditWanted = ditStateG 480 gp.m.ditEnabled = ditStateM 481 if !ditStateM { 482 sys.DisableDIT() 483 } 484 } 485 486 // Do not unwind m->g0->sched.sp. 487 // Our caller, cgocallback, will do that. 488 restore = false 489 } 490 491 func unwindm(restore *bool) { 492 if *restore { 493 // Restore sp saved by cgocallback during 494 // unwind of g's stack (see comment at top of file). 495 mp := acquirem() 496 sched := &mp.g0.sched 497 sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + alignUp(sys.MinFrameSize, sys.StackAlign))) 498 499 // Do the accounting that cgocall will not have a chance to do 500 // during an unwind. 501 // 502 // In the case where a Go call originates from C, ncgo is 0 503 // and there is no matching cgocall to end. 504 if mp.ncgo > 0 { 505 mp.incgo = false 506 mp.ncgo-- 507 } 508 509 // Undo the call to lockOSThread in cgocallbackg, only on the 510 // panicking path. In normal return case cgocallbackg will call 511 // unlockOSThread, ensuring no preemption point after the unlock. 512 // Here we don't need to worry about preemption, because we're 513 // panicking out of the callback and unwinding the g0 stack, 514 // instead of reentering cgo (which requires the same thread). 515 unlockOSThread() 516 517 releasem(mp) 518 } 519 } 520 521 // called from assembly. 522 func badcgocallback() { 523 throw("misaligned stack in cgocallback") 524 } 525 526 // called from (incomplete) assembly. 527 func cgounimpl() { 528 throw("cgo not implemented") 529 } 530 531 var racecgosync uint64 // represents possible synchronization in C code 532 533 // Pointer checking for cgo code. 534 535 // We want to detect all cases where a program that does not use 536 // unsafe makes a cgo call passing a Go pointer to memory that 537 // contains an unpinned Go pointer. Here a Go pointer is defined as a 538 // pointer to memory allocated by the Go runtime. Programs that use 539 // unsafe can evade this restriction easily, so we don't try to catch 540 // them. The cgo program will rewrite all possibly bad pointer 541 // arguments to call cgoCheckPointer, where we can catch cases of a Go 542 // pointer pointing to an unpinned Go pointer. 543 544 // Complicating matters, taking the address of a slice or array 545 // element permits the C program to access all elements of the slice 546 // or array. In that case we will see a pointer to a single element, 547 // but we need to check the entire data structure. 548 549 // The cgoCheckPointer call takes additional arguments indicating that 550 // it was called on an address expression. An additional argument of 551 // true means that it only needs to check a single element. An 552 // additional argument of a slice or array means that it needs to 553 // check the entire slice/array, but nothing else. Otherwise, the 554 // pointer could be anything, and we check the entire heap object, 555 // which is conservative but safe. 556 557 // When and if we implement a moving garbage collector, 558 // cgoCheckPointer will pin the pointer for the duration of the cgo 559 // call. (This is necessary but not sufficient; the cgo program will 560 // also have to change to pin Go pointers that cannot point to Go 561 // pointers.) 562 563 // cgoCheckPointer checks if the argument contains a Go pointer that 564 // points to an unpinned Go pointer, and panics if it does. 565 func cgoCheckPointer(ptr any, arg any) { 566 if !goexperiment.CgoCheck2 && debug.cgocheck == 0 { 567 return 568 } 569 570 ep := efaceOf(&ptr) 571 t := ep._type 572 573 top := true 574 if arg != nil && (t.Kind() == abi.Pointer || t.Kind() == abi.UnsafePointer) { 575 p := ep.data 576 if !t.IsDirectIface() { 577 p = *(*unsafe.Pointer)(p) 578 } 579 if p == nil || !cgoIsGoPointer(p) { 580 return 581 } 582 aep := efaceOf(&arg) 583 switch aep._type.Kind() { 584 case abi.Bool: 585 if t.Kind() == abi.UnsafePointer { 586 // We don't know the type of the element. 587 break 588 } 589 pt := (*ptrtype)(unsafe.Pointer(t)) 590 cgoCheckArg(pt.Elem, p, true, false, cgoCheckPointerFail) 591 return 592 case abi.Slice: 593 // Check the slice rather than the pointer. 594 ep = aep 595 t = ep._type 596 case abi.Array: 597 // Check the array rather than the pointer. 598 // Pass top as false since we have a pointer 599 // to the array. 600 ep = aep 601 t = ep._type 602 top = false 603 case abi.Pointer: 604 // The Go code is indexing into a pointer to an array, 605 // and we have been passed the pointer-to-array. 606 // Check the array rather than the pointer. 607 pt := (*abi.PtrType)(unsafe.Pointer(aep._type)) 608 t = pt.Elem 609 if t.Kind() != abi.Array { 610 throw("can't happen") 611 } 612 ep = aep 613 top = false 614 default: 615 throw("can't happen") 616 } 617 } 618 619 cgoCheckArg(t, ep.data, !t.IsDirectIface(), top, cgoCheckPointerFail) 620 } 621 622 type cgoErrorMsg int 623 624 const ( 625 cgoCheckPointerFail cgoErrorMsg = iota 626 cgoResultFail 627 ) 628 629 // cgoCheckArg is the real work of cgoCheckPointer and cgoCheckResult. 630 // The argument p is either a pointer to the value (of type t), or the value 631 // itself, depending on indir. The top parameter is whether we are at the top 632 // level, where Go pointers are allowed. Go pointers to pinned objects are 633 // allowed as long as they don't reference other unpinned pointers. 634 func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg cgoErrorMsg) { 635 if !t.Pointers() || p == nil { 636 // If the type has no pointers there is nothing to do. 637 return 638 } 639 640 switch t.Kind() { 641 default: 642 throw("can't happen") 643 case abi.Array: 644 at := (*arraytype)(unsafe.Pointer(t)) 645 if !indir { 646 if at.Len != 1 { 647 throw("can't happen") 648 } 649 cgoCheckArg(at.Elem, p, !at.Elem.IsDirectIface(), top, msg) 650 return 651 } 652 for i := uintptr(0); i < at.Len; i++ { 653 cgoCheckArg(at.Elem, p, true, top, msg) 654 p = add(p, at.Elem.Size_) 655 } 656 case abi.Chan, abi.Map: 657 // These types contain internal pointers that will 658 // always be allocated in the Go heap. It's never OK 659 // to pass them to C. 660 panic(cgoFormatErr(msg, t.Kind())) 661 case abi.Func: 662 if indir { 663 p = *(*unsafe.Pointer)(p) 664 } 665 if !cgoIsGoPointer(p) { 666 return 667 } 668 panic(cgoFormatErr(msg, t.Kind())) 669 case abi.Interface: 670 it := *(**_type)(p) 671 if it == nil { 672 return 673 } 674 // A type known at compile time is OK since it's 675 // constant. A type not known at compile time will be 676 // in the heap and will not be OK. 677 if inheap(uintptr(unsafe.Pointer(it))) { 678 panic(cgoFormatErr(msg, t.Kind())) 679 } 680 p = *(*unsafe.Pointer)(add(p, goarch.PtrSize)) 681 if !cgoIsGoPointer(p) { 682 return 683 } 684 if !top && !isPinned(p) { 685 panic(cgoFormatErr(msg, t.Kind())) 686 } 687 cgoCheckArg(it, p, !it.IsDirectIface(), false, msg) 688 case abi.Slice: 689 st := (*slicetype)(unsafe.Pointer(t)) 690 s := (*slice)(p) 691 p = s.array 692 if p == nil || !cgoIsGoPointer(p) { 693 return 694 } 695 if !top && !isPinned(p) { 696 panic(cgoFormatErr(msg, t.Kind())) 697 } 698 if !st.Elem.Pointers() { 699 return 700 } 701 for i := 0; i < s.cap; i++ { 702 cgoCheckArg(st.Elem, p, true, false, msg) 703 p = add(p, st.Elem.Size_) 704 } 705 case abi.String: 706 ss := (*stringStruct)(p) 707 if !cgoIsGoPointer(ss.str) { 708 return 709 } 710 if !top && !isPinned(ss.str) { 711 panic(cgoFormatErr(msg, t.Kind())) 712 } 713 case abi.Struct: 714 st := (*structtype)(unsafe.Pointer(t)) 715 if !indir { 716 if len(st.Fields) != 1 { 717 throw("can't happen") 718 } 719 cgoCheckArg(st.Fields[0].Typ, p, !st.Fields[0].Typ.IsDirectIface(), top, msg) 720 return 721 } 722 for _, f := range st.Fields { 723 if !f.Typ.Pointers() { 724 continue 725 } 726 cgoCheckArg(f.Typ, add(p, f.Offset), true, top, msg) 727 } 728 case abi.Pointer, abi.UnsafePointer: 729 if indir { 730 p = *(*unsafe.Pointer)(p) 731 if p == nil { 732 return 733 } 734 } 735 736 if !cgoIsGoPointer(p) { 737 return 738 } 739 if !top && !isPinned(p) { 740 panic(cgoFormatErr(msg, t.Kind())) 741 } 742 743 cgoCheckUnknownPointer(p, msg) 744 } 745 } 746 747 // cgoCheckUnknownPointer is called for an arbitrary pointer into Go 748 // memory. It checks whether that Go memory contains any other 749 // pointer into unpinned Go memory. If it does, we panic. 750 // The return values are unused but useful to see in panic tracebacks. 751 func cgoCheckUnknownPointer(p unsafe.Pointer, msg cgoErrorMsg) (base, i uintptr) { 752 if inheap(uintptr(p)) { 753 b, span, _ := findObject(uintptr(p), 0, 0) 754 base = b 755 if base == 0 { 756 return 757 } 758 tp := span.typePointersOfUnchecked(base) 759 for { 760 var addr uintptr 761 if tp, addr = tp.next(base + span.elemsize); addr == 0 { 762 break 763 } 764 pp := *(*unsafe.Pointer)(unsafe.Pointer(addr)) 765 if cgoIsGoPointer(pp) && !isPinned(pp) { 766 panic(cgoFormatErr(msg, abi.Pointer)) 767 } 768 } 769 return 770 } 771 772 for _, datap := range activeModules() { 773 if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) { 774 // We have no way to know the size of the object. 775 // We have to assume that it might contain a pointer. 776 panic(cgoFormatErr(msg, abi.Pointer)) 777 } 778 // In the text or noptr sections, we know that the 779 // pointer does not point to a Go pointer. 780 } 781 782 return 783 } 784 785 // cgoIsGoPointer reports whether the pointer is a Go pointer--a 786 // pointer to Go memory. We only care about Go memory that might 787 // contain pointers. 788 // 789 //go:nosplit 790 //go:nowritebarrierrec 791 func cgoIsGoPointer(p unsafe.Pointer) bool { 792 if p == nil { 793 return false 794 } 795 796 if inHeapOrStack(uintptr(p)) { 797 return true 798 } 799 800 for _, datap := range activeModules() { 801 if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) { 802 return true 803 } 804 } 805 806 return false 807 } 808 809 // cgoInRange reports whether p is between start and end. 810 // 811 //go:nosplit 812 //go:nowritebarrierrec 813 func cgoInRange(p unsafe.Pointer, start, end uintptr) bool { 814 return start <= uintptr(p) && uintptr(p) < end 815 } 816 817 // cgoCheckResult is called to check the result parameter of an 818 // exported Go function. It panics if the result is or contains any 819 // other pointer into unpinned Go memory. 820 func cgoCheckResult(val any) { 821 if !goexperiment.CgoCheck2 && debug.cgocheck == 0 { 822 return 823 } 824 825 ep := efaceOf(&val) 826 t := ep._type 827 if t == nil { 828 return 829 } 830 cgoCheckArg(t, ep.data, !t.IsDirectIface(), false, cgoResultFail) 831 } 832 833 // cgoFormatErr is called by cgoCheckArg and cgoCheckUnknownPointer 834 // to format panic error messages. 835 func cgoFormatErr(error cgoErrorMsg, kind abi.Kind) errorString { 836 var msg, kindname string 837 var cgoFunction string = "unknown" 838 var offset int 839 var buf [20]byte 840 841 // We expect one of these abi.Kind from cgoCheckArg 842 switch kind { 843 case abi.Chan: 844 kindname = "channel" 845 case abi.Func: 846 kindname = "function" 847 case abi.Interface: 848 kindname = "interface" 849 case abi.Map: 850 kindname = "map" 851 case abi.Pointer: 852 kindname = "pointer" 853 case abi.Slice: 854 kindname = "slice" 855 case abi.String: 856 kindname = "string" 857 case abi.Struct: 858 kindname = "struct" 859 case abi.UnsafePointer: 860 kindname = "unsafe pointer" 861 default: 862 kindname = "pointer" 863 } 864 865 // The cgo function name might need an offset to be obtained 866 if error == cgoResultFail { 867 offset = 21 868 } 869 870 // Relatively to cgoFormatErr, this is the stack frame: 871 // 0. cgoFormatErr 872 // 1. cgoCheckArg or cgoCheckUnknownPointer 873 // 2. cgoCheckPointer or cgoCheckResult 874 // 3. cgo function 875 pc, path, line, ok := Caller(3) 876 if ok && error == cgoResultFail { 877 function := FuncForPC(pc) 878 879 if function != nil { 880 // Expected format of cgo function name: 881 // - caller: _cgoexp_3c910ddb72c4_foo 882 if offset > len(function.Name()) { 883 cgoFunction = function.Name() 884 } else { 885 cgoFunction = function.Name()[offset:] 886 } 887 } 888 } 889 890 switch error { 891 case cgoResultFail: 892 msg = path + ":" + string(itoa(buf[:], uint64(line))) 893 msg += ": result of Go function " + cgoFunction + " called from cgo" 894 msg += " is unpinned Go " + kindname + " or points to unpinned Go " + kindname 895 case cgoCheckPointerFail: 896 msg += "argument of cgo function has Go pointer to unpinned Go " + kindname 897 } 898 899 return errorString(msg) 900 } 901