Try to use /proc on FreeBSD for getExecutablePath

Currently, clang's libTooling passes this function a fake argv0, which
means that no libTooling tools can find the standard headers on FreeBSD.
With this change, these will now work on any FreeBSD systems that have
procfs mounted.  This isn't the right fix for the libTooling issue, but
it does bring the FreeBSD implementation of getExecutablePath closer to
the Linux and macOS implementations.

llvm-svn: 359427

1 files changed, 14 insertions, 1 deletions

diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
index 0e150d1ac26..fa5115bfd65 100644
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -185,8 +185,21 @@ std::string getMainExecutable(const char *argv0, void *MainAddr) {
 #elif defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) ||   \
     defined(__minix) || defined(__DragonFly__) ||                              \
     defined(__FreeBSD_kernel__) || defined(_AIX)
+  StringRef curproc("/proc/curproc/file");
   char exe_path[PATH_MAX];
-
+  // /proc is not mounted by default under FreeBSD, but gives more accurate
+  // information than argv[0] when it is.
+  if (sys::fs::exists(curproc)) {
+    ssize_t len = readlink(curproc.str().c_str(), exe_path, sizeof(exe_path));
+    if (len > 0) {
+      // Null terminate the string for realpath. readlink never null
+      // terminates its output.
+      len = std::min(len, ssize_t(sizeof(exe_path) - 1));
+      exe_path[len] = '\0';
+      return exe_path;
+    }
+  }
+  // If we don't have procfs mounted, fall back to argv[0]
   if (getprogpath(exe_path, argv0) != NULL)
     return exe_path;
 #elif defined(__linux__) || defined(__CYGWIN__)