Deflake exec test.

- Only use MAXSYMLINKS/2+1 symlinks for each of the interpreter and script
  paths in SymlinkLimitRefreshedForInterpreter to tolerate cases where the
  original paths (/tmp, /bin, or /bin/echo) themselves contain symlinks.

- Ensure that UnshareFiles performs execve immediately after clone(CLONE_VFORK)
  (no heap allocation for ExecveArray/RunfilesPath).

- Use lstat() rather than stat() for the existence check in fs_util's Exists;
  the latter will fail if the symlink target does not exist, even if the
  symlink does.

PiperOrigin-RevId: 320110156

3 files changed, 9 insertions, 4 deletions

diff --git a/test/util/fs_util.cc b/test/util/fs_util.cc
index 052781445..5418948fe 100644
--- a/test/util/fs_util.cc
+++ b/test/util/fs_util.cc
@@ -125,12 +125,12 @@ PosixErrorOr<struct stat> Fstat(int fd) {
 
 PosixErrorOr<bool> Exists(absl::string_view path) {
   struct stat stat_buf;
-  int res = stat(std::string(path).c_str(), &stat_buf);
+  int res = lstat(std::string(path).c_str(), &stat_buf);
   if (res < 0) {
     if (errno == ENOENT) {
       return false;
     }
-    return PosixError(errno, absl::StrCat("stat ", path));
+    return PosixError(errno, absl::StrCat("lstat ", path));
   }
   return true;
 }
diff --git a/test/util/fs_util.h b/test/util/fs_util.h
index caf19b24d..8cdac23a1 100644
--- a/test/util/fs_util.h
+++ b/test/util/fs_util.h
@@ -44,9 +44,14 @@ PosixErrorOr<std::string> GetCWD();
 // can't be determined.
 PosixErrorOr<bool> Exists(absl::string_view path);
 
-// Returns a stat structure for the given path or an error.
+// Returns a stat structure for the given path or an error. If the path
+// represents a symlink, it will be traversed.
 PosixErrorOr<struct stat> Stat(absl::string_view path);
 
+// Returns a stat structure for the given path or an error. If the path
+// represents a symlink, it will not be traversed.
+PosixErrorOr<struct stat> Lstat(absl::string_view path);
+
 // Returns a stat struct for the given fd.
 PosixErrorOr<struct stat> Fstat(int fd);
 
diff --git a/test/util/temp_path.cc b/test/util/temp_path.cc
index 9c10b6674..e1bdee7fd 100644
--- a/test/util/temp_path.cc
+++ b/test/util/temp_path.cc
@@ -56,7 +56,7 @@ void TryDeleteRecursively(std::string const& path) {
     if (undeleted_dirs || undeleted_files || !status.ok()) {
       std::cerr << path << ": failed to delete " << undeleted_dirs
                 << " directories and " << undeleted_files
-                << " files: " << status;
+                << " files: " << status << std::endl;
     }
   }
 }