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// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// +build libc_exec
package main
// #include <errno.h>
// #include <stdio.h>
// #include <stdlib.h>
// #include <string.h>
// #include <unistd.h>
// #include <sys/types.h>
// #include <sys/wait.h>
//
// int libc_exec(const char *pathname, char *const argv[], char *const envp[]) {
// // Since fork() brings us to one thread, we can only use async-signal-safe funcs below.
// pid_t pid = fork();
// if (pid == 0) {
// execve(pathname, argv, envp);
// fprintf(stderr, "exec failed (errno: %d)\n", errno);
// _exit(1);
// }
// if (pid < 0) {
// return errno;
// }
//
// int wstatus;
// pid_t waited = waitpid(pid, &wstatus, 0);
// if (waited == -1) {
// return errno;
// }
// exit(WEXITSTATUS(wstatus));
//}
import "C"
import (
"os/exec"
"unsafe"
)
// Replacement for syscall.Execve that uses the libc.
// This allows tools that rely on intercepting syscalls via
// LD_PRELOAD to work properly (e.g. gentoo sandbox).
// Note that this changes the go binary to be a dynamically linked one.
// See crbug.com/1000863 for details.
// To use this version of exec, please add '-tags libc_exec' when building Go binary.
// Without the tags, libc_exec.go will not be used.
func execCmd(env env, cmd *command) error {
freeList := []unsafe.Pointer{}
defer func() {
for _, ptr := range freeList {
C.free(ptr)
}
}()
goStrToC := func(goStr string) *C.char {
cstr := C.CString(goStr)
freeList = append(freeList, unsafe.Pointer(cstr))
return cstr
}
goSliceToC := func(goSlice []string) **C.char {
// len(goSlice)+1 as the c array needs to be null terminated.
cArray := C.malloc(C.size_t(len(goSlice)+1) * C.size_t(unsafe.Sizeof(uintptr(0))))
freeList = append(freeList, cArray)
// Convert the C array to a Go Array so we can index it.
// Note: Storing pointers to the c heap in go pointer types is ok
// (see https://golang.org/cmd/cgo/).
cArrayForIndex := (*[1<<30 - 1]*C.char)(cArray)
for i, str := range goSlice {
cArrayForIndex[i] = goStrToC(str)
}
cArrayForIndex[len(goSlice)] = nil
return (**C.char)(cArray)
}
execCmd := exec.Command(cmd.Path, cmd.Args...)
mergedEnv := mergeEnvValues(env.environ(), cmd.EnvUpdates)
if errno := C.libc_exec(goStrToC(execCmd.Path), goSliceToC(execCmd.Args), goSliceToC(mergedEnv)); errno != 0 {
return newErrorwithSourceLocf("exec error: %d", errno)
}
return nil
}
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