Implement argv0-less getMainExecutable for FreeBSD

[emaste]

Summary

The llvm-symbolizer patch in D5610 needs to call getMainExecutable without argv0.

Today this works on Linux, which reads /proc/self/exe, but does not on FreeBSD and other operating systems, which determine the exe name from argv0.

On FreeBSD the exe name can be found from the kern.proc.pathname sysctl. This probably works on other BSDs as well; others can confirm and update the #ifdefs.

[emaste]

Add NetBSD #ifdefs

[joerg]

I would prefer using dl_iterate_phdr for this, I think.

[emaste]

I would prefer using dl_iterate_phdr for this, I think.

Ahh, good point - for some reason I thought it did not include the executable itself, but a quick test confirms it behaves as expected on FreeBSD stable/10 at least. That said, I don't see a guarantee that the first result returned is the executable.

[joerg]

Hm. Right, it's not required to be. OK, I guess the sysctl is the best answer, __ps_strings might have a relative path or so.

[samsonov]

LGTM

[Eugene.Zelenko]

Looks like patch was not committed.

[jbeich]

lib/Support/Unix/Path.inc

51

Add || defined(__DragonFly__) as it has KERN_PROC_PATHNAME.

167–178

Add || defined(__DragonFly__) as its KERN_PROC_PATHNAME is similar to FreeBSD.

171

Not valid on NetBSD, see sysctl(7). Try instead:

#if defined(__NetBSD__)
  int name[4] = { CTL_KERN, KERN_PROC_ARGS, -1, KERN_PROC_PATHNAME};
#else
  int name[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };
#endif

173

getpid() can be optimized to -1. Other LLVM consumers of KERN_PROC_PATHNAME already use -1.

lib/Support/Unix/Path.inc

 # if HAVE_NDIR_H
 #  include <ndir.h>
 # endif
 #endif
 
 #ifdef __APPLE__
 #include <mach-o/dyld.h>
 #endif
+#if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+#include <sys/sysctl.h>
+#endif
 
 // Both stdio.h and cstdio are included via different pathes and
 // stdcxx's cstdio doesn't include stdio.h, so it doesn't #undef the macros
 // either.
 #undef ferror
 #undef feof
 
 // For GNU Hurd
#if defined(__APPLE__)
   // binaries with symbols.
   char exe_path[MAXPATHLEN];
   uint32_t size = sizeof(exe_path);
   if (_NSGetExecutablePath(exe_path, &size) == 0) {
     char link_path[MAXPATHLEN];
     if (realpath(exe_path, link_path))
       return link_path;
   }
-#elif defined(__FreeBSD__) || defined (__NetBSD__) || defined(__Bitrig__) || \
-      defined(__OpenBSD__) || defined(__minix) || defined(__DragonFly__) || \
-      defined(__FreeBSD_kernel__)
+#elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+  char exe_path[MAXPATHLEN];
+  size_t len = sizeof(exe_path);
+  int name[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME };
+
+  name[3] = getpid();
+  if (sysctl(name, 4, exe_path, &len, NULL, 0) == 0)
+    return exe_path;
+  else if (argv0 != nullptr && getprogpath(exe_path, argv0) != nullptr)
+    return exe_path;
+#elif defined(__NetBSD__) || defined(__Bitrig__) || \
+      defined(__OpenBSD__) || defined(__minix) || defined(__DragonFly__)
   char exe_path[PATH_MAX];
 
   if (getprogpath(exe_path, argv0) != NULL)
     return exe_path;
 #elif defined(__linux__) || defined(__CYGWIN__)
   char exe_path[MAXPATHLEN];
   StringRef aPath("/proc/self/exe");
   if (sys::fs::exists(aPath)) {