[llvm] r219170 - Support: Add a utility to remap std{in, out, err} to /dev/null if closed
David Majnemer
david.majnemer at gmail.com
Mon Oct 6 16:16:18 PDT 2014
Author: majnemer
Date: Mon Oct 6 18:16:18 2014
New Revision: 219170
URL: http://llvm.org/viewvc/llvm-project?rev=219170&view=rev
Log:
Support: Add a utility to remap std{in,out,err} to /dev/null if closed
It's possible to start a program with one (or all) of the standard file
descriptors closed. Subsequent open system calls will give the program
a low-numbered file descriptor.
This is problematic because we may believe we are writing to standard
out instead of a file.
Introduce Process::FixupStandardFileDescriptors, a helper function to
remap standard file descriptors to /dev/null if they were closed before
the program started.
Modified:
llvm/trunk/include/llvm/Support/Process.h
llvm/trunk/lib/Support/Unix/Process.inc
llvm/trunk/lib/Support/Windows/Process.inc
Modified: llvm/trunk/include/llvm/Support/Process.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Process.h?rev=219170&r1=219169&r2=219170&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/Process.h (original)
+++ llvm/trunk/include/llvm/Support/Process.h Mon Oct 6 18:16:18 2014
@@ -186,6 +186,12 @@ public:
ArrayRef<const char *> ArgsFromMain,
SpecificBumpPtrAllocator<char> &ArgAllocator);
+ // This functions ensures that the standard file descriptors (input, output,
+ // and error) are properly mapped to a file descriptor before we use any of
+ // them. This should only be called by standalone programs, library
+ // components should not call this.
+ static std::error_code FixupStandardFileDescriptors();
+
/// This function determines if the standard input is connected directly
/// to a user's input (keyboard probably), rather than coming from a file
/// or pipe.
Modified: llvm/trunk/lib/Support/Unix/Process.inc
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Unix/Process.inc?rev=219170&r1=219169&r2=219170&view=diff
==============================================================================
--- llvm/trunk/lib/Support/Unix/Process.inc (original)
+++ llvm/trunk/lib/Support/Unix/Process.inc Mon Oct 6 18:16:18 2014
@@ -18,6 +18,9 @@
#include "llvm/Support/Mutex.h"
#include "llvm/Support/MutexGuard.h"
#include "llvm/Support/TimeValue.h"
+#if HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
@@ -199,6 +202,62 @@ Process::GetArgumentVector(SmallVectorIm
return std::error_code();
}
+namespace {
+class FDCloser {
+public:
+ FDCloser(int &FD) : FD(FD), KeepOpen(false) {}
+ void keepOpen() { KeepOpen = true; }
+ ~FDCloser() {
+ if (!KeepOpen && FD >= 0)
+ ::close(FD);
+ }
+
+private:
+ FDCloser(const FDCloser &) LLVM_DELETED_FUNCTION;
+ void operator=(const FDCloser &) LLVM_DELETED_FUNCTION;
+
+ int &FD;
+ bool KeepOpen;
+};
+}
+
+std::error_code Process::FixupStandardFileDescriptors() {
+ int NullFD = -1;
+ FDCloser FDC(NullFD);
+ const int StandardFDs[] = {STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO};
+ for (int StandardFD : StandardFDs) {
+ struct stat st;
+ errno = 0;
+ while (fstat(StandardFD, &st) < 0) {
+ assert(errno && "expected errno to be set if fstat failed!");
+ // fstat should return EBADF if the file descriptor is closed.
+ if (errno == EBADF)
+ break;
+ // retry fstat if we got EINTR, otherwise bubble up the failure.
+ if (errno != EINTR)
+ return std::error_code(errno, std::generic_category());
+ }
+ // if fstat succeeds, move on to the next FD.
+ if (!errno)
+ continue;
+ assert(errno == EBADF && "expected errno to have EBADF at this point!");
+
+ if (NullFD < 0) {
+ while ((NullFD = open("/dev/null", O_RDWR)) < 0) {
+ if (errno == EINTR)
+ continue;
+ return std::error_code(errno, std::generic_category());
+ }
+ }
+
+ if (NullFD == StandardFD)
+ FDC.keepOpen();
+ else if (dup2(NullFD, StandardFD) < 0)
+ return std::error_code(errno, std::generic_category());
+ }
+ return std::error_code();
+}
+
bool Process::StandardInIsUserInput() {
return FileDescriptorIsDisplayed(STDIN_FILENO);
}
Modified: llvm/trunk/lib/Support/Windows/Process.inc
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Windows/Process.inc?rev=219170&r1=219169&r2=219170&view=diff
==============================================================================
--- llvm/trunk/lib/Support/Windows/Process.inc (original)
+++ llvm/trunk/lib/Support/Windows/Process.inc Mon Oct 6 18:16:18 2014
@@ -273,6 +273,10 @@ Process::GetArgumentVector(SmallVectorIm
return ec;
}
+std::error_code Process::FixupStandardFileDescriptors() {
+ return std::error_code();
+}
+
bool Process::StandardInIsUserInput() {
return FileDescriptorIsDisplayed(0);
}
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