On Linux, clear the signal mask of the launched inferior

Summary:
Due to fork()/execve(), the launched inferior inherits the signal mask of its parent (lldb-server). But because lldb-server modifies its signal mask (It blocks SIGCHLD, for example), the inferior starts with some signals being initially blocked.

One consequence is that TestCallThatRestarts.ExprCommandThatRestartsTestCase (test/expression_command/call-restarts) fails because sigchld_handler() in lotta-signals.c is not called, due to the SIGCHLD signal being blocked.

To prevent the signal masking done by lldb-server from affecting the created inferior, the signal mask of the inferior is now cleared before the execve().

Patch by: Yacine Belkadi

Reviewers: ovyalov, labath

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D12138

llvm-svn: 245436

lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp

@@ -554,7 +554,8 @@ NativeProcessLinux::Launch(LaunchArgs *args, Error &error)
         eDupStderrFailed,
         eChdirFailed,
         eExecFailed,
-        eSetGidFailed
+        eSetGidFailed,
+        eSetSigMaskFailed
     };
 
     // Child process.
@@ -632,6 +633,12 @@ NativeProcessLinux::Launch(LaunchArgs *args, Error &error)
             }
         }
 
+        // Clear the signal mask to prevent the child from being affected by
+        // any masking done by the parent.
+        sigset_t set;
+        if (sigemptyset(&set) != 0 || pthread_sigmask(SIG_SETMASK, &set, nullptr) != 0)
+            exit(eSetSigMaskFailed);
+
         // Execute.  We should never return...
         execve(argv[0],
                const_cast<char *const *>(argv),
@@ -689,6 +696,9 @@ NativeProcessLinux::Launch(LaunchArgs *args, Error &error)
             case eSetGidFailed:
                 error.SetErrorString("Child setgid failed.");
                 break;
+            case eSetSigMaskFailed:
+                error.SetErrorString("Child failed to set signal mask.");
+                break;
             default:
                 error.SetErrorString("Child returned unknown exit status.");
                 break;

lldb/test/expression_command/call-restarts/TestCallThatRestarts.py

@@ -29,7 +29,6 @@ class ExprCommandThatRestartsTestCase(TestBase):
 
     @dwarf_test
     @skipIfFreeBSD # llvm.org/pr19246: intermittent failure
-    @expectedFailureLinux("llvm.org/pr19246")
     @skipIfDarwin # llvm.org/pr19246: intermittent failure
     @skipIfWindows # Test relies on signals, unsupported on Windows
     def test_with_dwarf(self):