fakecgo: C functions require nosplit (#295)

* fakecgo: C functions require nosplit

fakecgo runs on systemstack so we shouldn't ever split the stack.

Fixes #287

.github/workflows/test.yml

@@ -96,7 +96,7 @@ jobs:
           # Compile without optimization to check potential stack overflow.
           # The option '-gcflags=all=-N -l' is often used at Visual Studio Code.
           # See also https://go.googlesource.com/vscode-go/+/HEAD/docs/debugging.md#launch.
-          # TODO: CGO_ENABLED=0 might cause SEGV. Fix this issue.
+          env CGO_ENABLED=0 go test "-gcflags=all=-N -l" -v ./...
           env CGO_ENABLED=1 go test "-gcflags=all=-N -l" -v ./...
 
       - name: go test (Linux arm64)

internal/fakecgo/gen.go

@@ -36,6 +36,7 @@ func setg_trampoline(setg uintptr, G uintptr)
 func call5(fn, a1, a2, a3, a4, a5 uintptr) uintptr
 
 {{ range . -}}
+//go:nosplit
 func {{.Name}}(
 {{- range .Args -}}
 	{{- if .Name -}}

internal/fakecgo/go_libinit.go

@@ -50,17 +50,20 @@ func _cgo_try_pthread_create(thread *pthread_t, attr *pthread_attr_t, pfn unsafe
 	var err int
 
 	for tries = 0; tries < 20; tries++ {
-		err = int(pthread_create(thread, attr, pfn, unsafe.Pointer(arg)))
+		// inlined this call because it ran out of stack when inlining was disabled
+		err = int(call5(pthread_createABI0, uintptr(unsafe.Pointer(thread)), uintptr(unsafe.Pointer(attr)), uintptr(pfn), uintptr(unsafe.Pointer(arg)), 0))
 		if err == 0 {
-			pthread_detach(*thread)
+			// inlined this call because it ran out of stack when inlining was disabled
+			call5(pthread_detachABI0, uintptr(*thread), 0, 0, 0, 0)
 			return 0
 		}
 		if err != int(syscall.EAGAIN) {
 			return err
 		}
 		ts.Sec = 0
 		ts.Nsec = (tries + 1) * 1000 * 1000 // Milliseconds.
-		nanosleep(&ts, nil)
+		// inlined this call because it ran out of stack when inlining was disabled
+		call5(nanosleepABI0, uintptr(unsafe.Pointer(&ts)), 0, 0, 0, 0)
 	}
 	return int(syscall.EAGAIN)
 }

internal/fakecgo/libcgo.go

@@ -6,7 +6,11 @@
 package fakecgo
 
 type (
-	size_t         uintptr
+	size_t uintptr
+	// Sources:
+	// Darwin (32 bytes) - https://github.com/apple/darwin-xnu/blob/2ff845c2e033bd0ff64b5b6aa6063a1f8f65aa32/bsd/sys/_types.h#L74
+	// FreeBSD (32 bytes) - https://github.com/DoctorWkt/xv6-freebsd/blob/d2a294c2a984baed27676068b15ed9a29b06ab6f/include/signal.h#L98C9-L98C21
+	// Linux (128 bytes) - https://github.com/torvalds/linux/blob/ab75170520d4964f3acf8bb1f91d34cbc650688e/arch/x86/include/asm/signal.h#L25
 	sigset_t       [128]byte
 	pthread_attr_t [64]byte
 	pthread_t      int