[sanitizer] Implement internal_fork and internal_forkpty for OS X

On Linux, we have internal_fork that forks without invoking user's pthread_atfork handlers, which is important for spawning external symbolizers. Let's implement this for OS X as well (using __fork). This patch also adds internal_forkpty which re-implements forkpty and uses __fork in it as well.

Differential Revision: http://reviews.llvm.org/D14869

llvm-svn: 253666

compiler-rt/lib/sanitizer_common/sanitizer_mac.cc

@@ -52,6 +52,7 @@ extern char **environ;
 #include <sys/sysctl.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <util.h>
 
 namespace __sanitizer {
 
@@ -147,9 +148,30 @@ uptr internal_sigprocmask(int how, __sanitizer_sigset_t *set,
   return sigprocmask(how, set, oldset);
 }
 
+// Doesn't call pthread_atfork() handlers.
+extern "C" pid_t __fork(void);
+
 int internal_fork() {
-  // TODO(glider): this may call user's pthread_atfork() handlers which is bad.
-  return fork();
+  return __fork();
+}
+
+int internal_forkpty(int *amaster) {
+  int master, slave;
+  if (openpty(&master, &slave, nullptr, nullptr, nullptr) == -1) return -1;
+  int pid = __fork();
+  if (pid == -1) {
+    close(master);
+    close(slave);
+    return -1;
+  }
+  if (pid == 0) {
+    close(master);
+    CHECK_EQ(login_tty(slave), 0);
+  } else {
+    *amaster = master;
+    close(slave);
+  }
+  return pid;
 }
 
 uptr internal_rename(const char *oldpath, const char *newpath) {

compiler-rt/lib/sanitizer_common/sanitizer_posix.h

@@ -54,6 +54,7 @@ uptr internal_ptrace(int request, int pid, void *addr, void *data);
 uptr internal_waitpid(int pid, int *status, int options);
 
 int internal_fork();
+int internal_forkpty(int *amaster);
 
 // These functions call appropriate pthread_ functions directly, bypassing
 // the interceptor. They are weak and may not be present in some tools.

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

@@ -75,7 +75,7 @@ bool SymbolizerProcess::StartSymbolizerSubprocess() {
 #if SANITIZER_MAC
     fd_t fd = kInvalidFd;
     // Use forkpty to disable buffering in the new terminal.
-    pid = forkpty(&fd, 0, 0, 0);
+    pid = internal_forkpty(&fd);
     if (pid == -1) {
       // forkpty() failed.
       Report("WARNING: failed to fork external symbolizer (errno: %d)\n",