[all-commits] [llvm/llvm-project] 44aaca: [libFuzzer] Allow discarding output in ExecuteComm...

[Marco Vanotti via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 44aaca3de4f4918b6178a28d855b153ab335e6a3
      https://github.com/llvm/llvm-project/commit/44aaca3de4f4918b6178a28d855b153ab335e6a3
  Author: Marco Vanotti <mvanotti at google.com>
  Date:   2020-01-17 (Fri, 17 Jan 2020)

  Changed paths:
    M compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp

  Log Message:
  -----------
  [libFuzzer] Allow discarding output in ExecuteCommand in Fuchsia.

Summary:
This commit modifies the way `ExecuteCommand` works in fuchsia by adding
special logic to handle `/dev/null`.

The FuzzerCommand interface does not have a way to "discard" the output,
so other parts of the code just set the output file to `getDevNull()`.
The problem is that fuchsia does not have a named file that is
equivalent to `/dev/null`, so opening that file just fails.

This commit detects whether the specified output file is `getDevNull`,
and if that's the case, it will not copy the file descriptor for stdout
in the spawned process.

NOTE that modifying `FuzzerCommand` to add a "discardOutput" function
involves a significant refactor of all the other platforms, as they all
rely on the `toString()` method of `FuzzerCommand`.

This allows libfuzzer in fuchsia to run with `fork=1`, as the merge
process (`FuzzerMerge.cpp`) invoked `ExecuteCommand` with `/dev/null` as the
output.

Reviewers: aarongreen, phosek

Reviewed By: aarongreen

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D72894