code review 4253052: os, syscall: add ProcAttributes type. Change StartProce...

src/pkg/syscall/exec_unix.go

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Fork, exec, wait, etc.
 
 package syscall
 
 import (
         "sync"
@@ skipping 85 matching lines @@
 // no rescheduling, no malloc calls, and no new stack segments.
 // The calls to RawSyscall are okay because they are assembly
 // functions that do not grow the stack.
 func forkAndExecInChild(argv0 *byte, argv, envv []*byte, dir *byte, attr *ProcAttr, pipe int) (pid int, err int) {
         // Declare all variables at top in case any
         // declarations require heap allocation (e.g., err1).
         var r1, r2, err1 uintptr
         var nextfd int
         var i int
 
-        // we could copy this if we cared about the side effects, but this is syscall.
-        fd := attr.Files
+        // guard against side effects of shuffling fds below.
+        fd := append([]int(nil), attr.Files...)
 
         darwin := OS == "darwin"
 
         // About to call fork.
         // No more allocation or calls of non-assembly functions.
         r1, r2, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
         if err1 != 0 {
                 return 0, int(err1)
         }
 
@@ skipping 217 matching lines @@
 }
 
 // Ordinary exec.
 func Exec(argv0 string, argv []string, envv []string) (err int) {
         _, _, err1 := RawSyscall(SYS_EXECVE,
                 uintptr(unsafe.Pointer(StringBytePtr(argv0))),
                 uintptr(unsafe.Pointer(&StringArrayPtr(argv)[0])),
                 uintptr(unsafe.Pointer(&StringArrayPtr(envv)[0])))
         return int(err1)
 }