[PATCH] D68774: [libFuzzer] Don't prefix absolute paths in fuchsia.

[Marco Vanotti via Phabricator via llvm-commits]

charco created this revision.
charco added reviewers: mcgrathr, jakehehrlich, phosek, kcc, aarongreen.
Herald added projects: Sanitizers, LLVM.
Herald added subscribers: llvm-commits, Sanitizers.

The ExecuteCommand function in fuchsia used to prefix the
`getOutputFile` for each command run with the `artifact_prefix` flag if
it was available, because fuchsia components don't have a writable working
directory. However, if a file with a global path is provided, fuchsia
should honor that.

An example of this is using the global `/tmp` directory to store stuff.
In fuchsia it ended up being translated to `data///tmp`, whereas we want
to make sure it is using `/tmp` (which is available to components using the
`isolated-temp` feature).

To test this I made the change, compiled fuchsia with this toolchain and
ran a fuzzer with the `-fork=1` flag (that mode makes use of the `/tmp`
directory). I also tested that normal fuzzing workflow was not affected
by this.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D68774

Files:
  compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp


Index: compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
+++ compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
@@ -407,13 +407,14 @@
   // that lacks a mutable working directory. Fortunately, when this is the case
   // a mutable output directory must be specified using "-artifact_prefix=...",
   // so write the log file(s) there.
+  // However, we don't want to apply this logic for absolute paths.
   int FdOut = STDOUT_FILENO;
   if (Cmd.hasOutputFile()) {
-    std::string Path;
-    if (Cmd.hasFlag("artifact_prefix"))
-      Path = Cmd.getFlagValue("artifact_prefix") + "/" + Cmd.getOutputFile();
-    else
-      Path = Cmd.getOutputFile();
+    std::string Path = Cmd.getOutputFile();
+    bool IsAbsolutePath = Path.length() > 1 && Path[0] == '/';
+    if (!IsAbsolutePath && Cmd.hasFlag("artifact_prefix")) {
+      Path = Cmd.getFlagValue("artifact_prefix") + "/" + Path;
+    }
     FdOut = open(Path.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0);
     if (FdOut == -1) {
       Printf("libFuzzer: failed to open %s: %s\n", Path.c_str(),


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