diff options
Diffstat (limited to 'src/runtime/cgocall.go')
| -rw-r--r-- | src/runtime/cgocall.go | 166 |
1 files changed, 62 insertions, 104 deletions
diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go index 427ed0ffb9..9bca279318 100644 --- a/src/runtime/cgocall.go +++ b/src/runtime/cgocall.go @@ -35,47 +35,52 @@ // cgo writes a gcc-compiled function named GoF (not p.GoF, since gcc doesn't // know about packages). The gcc-compiled C function f calls GoF. // -// GoF calls crosscall2(_cgoexp_GoF, frame, framesize). Crosscall2 -// (in cgo/gcc_$GOARCH.S, a gcc-compiled assembly file) is a two-argument -// adapter from the gcc function call ABI to the 6c function call ABI. -// It is called from gcc to call 6c functions. In this case it calls -// _cgoexp_GoF(frame, framesize), still running on m->g0's stack -// and outside the $GOMAXPROCS limit. Thus, this code cannot yet -// call arbitrary Go code directly and must be careful not to allocate -// memory or use up m->g0's stack. +// GoF initializes "frame", a structure containing all of its +// arguments and slots for p.GoF's results. It calls +// crosscall2(_cgoexp_GoF, frame, framesize, ctxt) using the gcc ABI. // -// _cgoexp_GoF calls runtime.cgocallback(p.GoF, frame, framesize, ctxt). -// (The reason for having _cgoexp_GoF instead of writing a crosscall3 -// to make this call directly is that _cgoexp_GoF, because it is compiled -// with 6c instead of gcc, can refer to dotted names like -// runtime.cgocallback and p.GoF.) +// crosscall2 (in cgo/asm_$GOARCH.s) is a four-argument adapter from +// the gcc function call ABI to the gc function call ABI. At this +// point we're in the Go runtime, but we're still running on m.g0's +// stack and outside the $GOMAXPROCS limit. crosscall2 calls +// runtime.cgocallback(_cgoexp_GoF, frame, ctxt) using the gc ABI. +// (crosscall2's framesize argument is no longer used, but there's one +// case where SWIG calls crosscall2 directly and expects to pass this +// argument. See _cgo_panic.) // -// runtime.cgocallback (in asm_$GOARCH.s) switches from m->g0's -// stack to the original g (m->curg)'s stack, on which it calls -// runtime.cgocallbackg(p.GoF, frame, framesize). -// As part of the stack switch, runtime.cgocallback saves the current -// SP as m->g0->sched.sp, so that any use of m->g0's stack during the -// execution of the callback will be done below the existing stack frames. -// Before overwriting m->g0->sched.sp, it pushes the old value on the -// m->g0 stack, so that it can be restored later. +// runtime.cgocallback (in asm_$GOARCH.s) switches from m.g0's stack +// to the original g (m.curg)'s stack, on which it calls +// runtime.cgocallbackg(_cgoexp_GoF, frame, ctxt). As part of the +// stack switch, runtime.cgocallback saves the current SP as +// m.g0.sched.sp, so that any use of m.g0's stack during the execution +// of the callback will be done below the existing stack frames. +// Before overwriting m.g0.sched.sp, it pushes the old value on the +// m.g0 stack, so that it can be restored later. // // runtime.cgocallbackg (below) is now running on a real goroutine -// stack (not an m->g0 stack). First it calls runtime.exitsyscall, which will +// stack (not an m.g0 stack). First it calls runtime.exitsyscall, which will // block until the $GOMAXPROCS limit allows running this goroutine. // Once exitsyscall has returned, it is safe to do things like call the memory -// allocator or invoke the Go callback function p.GoF. runtime.cgocallbackg -// first defers a function to unwind m->g0.sched.sp, so that if p.GoF -// panics, m->g0.sched.sp will be restored to its old value: the m->g0 stack -// and the m->curg stack will be unwound in lock step. -// Then it calls p.GoF. Finally it pops but does not execute the deferred -// function, calls runtime.entersyscall, and returns to runtime.cgocallback. +// allocator or invoke the Go callback function. runtime.cgocallbackg +// first defers a function to unwind m.g0.sched.sp, so that if p.GoF +// panics, m.g0.sched.sp will be restored to its old value: the m.g0 stack +// and the m.curg stack will be unwound in lock step. +// Then it calls _cgoexp_GoF(frame). +// +// _cgoexp_GoF, which was generated by cmd/cgo, unpacks the arguments +// from frame, calls p.GoF, writes the results back to frame, and +// returns. Now we start unwinding this whole process. +// +// runtime.cgocallbackg pops but does not execute the deferred +// function to unwind m.g0.sched.sp, calls runtime.entersyscall, and +// returns to runtime.cgocallback. // // After it regains control, runtime.cgocallback switches back to -// m->g0's stack (the pointer is still in m->g0.sched.sp), restores the old -// m->g0.sched.sp value from the stack, and returns to _cgoexp_GoF. +// m.g0's stack (the pointer is still in m.g0.sched.sp), restores the old +// m.g0.sched.sp value from the stack, and returns to crosscall2. // -// _cgoexp_GoF immediately returns to crosscall2, which restores the -// callee-save registers for gcc and returns to GoF, which returns to f. +// crosscall2 restores the callee-save registers for gcc and returns +// to GoF, which unpacks any result values and returns to f. package runtime @@ -89,6 +94,22 @@ import ( // Length must match arg.Max in x_cgo_callers in runtime/cgo/gcc_traceback.c. type cgoCallers [32]uintptr +// argset matches runtime/cgo/linux_syscall.c:argset_t +type argset struct { + args unsafe.Pointer + retval uintptr +} + +// wrapper for syscall package to call cgocall for libc (cgo) calls. +//go:linkname syscall_cgocaller syscall.cgocaller +//go:nosplit +//go:uintptrescapes +func syscall_cgocaller(fn unsafe.Pointer, args ...uintptr) uintptr { + as := argset{args: unsafe.Pointer(&args[0])} + cgocall(fn, unsafe.Pointer(&as)) + return as.retval +} + // Call from Go to C. // // This must be nosplit because it's used for syscalls on some @@ -176,7 +197,7 @@ func cgocall(fn, arg unsafe.Pointer) int32 { // Call from C back to Go. //go:nosplit -func cgocallbackg(ctxt uintptr) { +func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) { gp := getg() if gp != gp.m.curg { println("runtime: bad g in cgocallback") @@ -204,7 +225,7 @@ func cgocallbackg(ctxt uintptr) { osPreemptExtExit(gp.m) - cgocallbackg1(ctxt) + cgocallbackg1(fn, frame, ctxt) // At this point unlockOSThread has been called. // The following code must not change to a different m. @@ -219,7 +240,7 @@ func cgocallbackg(ctxt uintptr) { gp.m.syscall = syscall } -func cgocallbackg1(ctxt uintptr) { +func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) { gp := getg() if gp.m.needextram || atomic.Load(&extraMWaiters) > 0 { gp.m.needextram = false @@ -263,79 +284,16 @@ func cgocallbackg1(ctxt uintptr) { raceacquire(unsafe.Pointer(&racecgosync)) } - type args struct { - fn *funcval - arg unsafe.Pointer - argsize uintptr - } - var cb *args - - // Location of callback arguments depends on stack frame layout - // and size of stack frame of cgocallback_gofunc. - sp := gp.m.g0.sched.sp - switch GOARCH { - default: - throw("cgocallbackg is unimplemented on arch") - case "arm": - // On arm, stack frame is two words and there's a saved LR between - // SP and the stack frame and between the stack frame and the arguments. - cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) - case "arm64": - // On arm64, stack frame is four words and there's a saved LR between - // SP and the stack frame and between the stack frame and the arguments. - // Additional two words (16-byte alignment) are for saving FP. - cb = (*args)(unsafe.Pointer(sp + 7*sys.PtrSize)) - case "amd64": - // On amd64, stack frame is two words, plus caller PC and BP. - cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) - case "386": - // On 386, stack frame is three words, plus caller PC. - cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) - case "ppc64", "ppc64le", "s390x": - // On ppc64 and s390x, the callback arguments are in the arguments area of - // cgocallback's stack frame. The stack looks like this: - // +--------------------+------------------------------+ - // | | ... | - // | cgoexp_$fn +------------------------------+ - // | | fixed frame area | - // +--------------------+------------------------------+ - // | | arguments area | - // | cgocallback +------------------------------+ <- sp + 2*minFrameSize + 2*ptrSize - // | | fixed frame area | - // +--------------------+------------------------------+ <- sp + minFrameSize + 2*ptrSize - // | | local variables (2 pointers) | - // | cgocallback_gofunc +------------------------------+ <- sp + minFrameSize - // | | fixed frame area | - // +--------------------+------------------------------+ <- sp - cb = (*args)(unsafe.Pointer(sp + 2*sys.MinFrameSize + 2*sys.PtrSize)) - case "mips64", "mips64le": - // On mips64x, stack frame is two words and there's a saved LR between - // SP and the stack frame and between the stack frame and the arguments. - cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) - case "mips", "mipsle": - // On mipsx, stack frame is two words and there's a saved LR between - // SP and the stack frame and between the stack frame and the arguments. - cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) - } - - // Invoke callback. - // NOTE(rsc): passing nil for argtype means that the copying of the - // results back into cb.arg happens without any corresponding write barriers. - // For cgo, cb.arg points into a C stack frame and therefore doesn't - // hold any pointers that the GC can find anyway - the write barrier - // would be a no-op. - reflectcall(nil, unsafe.Pointer(cb.fn), cb.arg, uint32(cb.argsize), 0) + // Invoke callback. This function is generated by cmd/cgo and + // will unpack the argument frame and call the Go function. + var cb func(frame unsafe.Pointer) + cbFV := funcval{uintptr(fn)} + *(*unsafe.Pointer)(unsafe.Pointer(&cb)) = noescape(unsafe.Pointer(&cbFV)) + cb(frame) if raceenabled { racereleasemerge(unsafe.Pointer(&racecgosync)) } - if msanenabled { - // Tell msan that we wrote to the entire argument block. - // This tells msan that we set the results. - // Since we have already called the function it doesn't - // matter that we are writing to the non-result parameters. - msanwrite(cb.arg, cb.argsize) - } // Do not unwind m->g0->sched.sp. // Our caller, cgocallback, will do that. |