[lldb] Fix write only file action to truncate the file

lldb/source/Host/common/FileAction.cpp

@@ -41,7 +41,7 @@ bool FileAction::Open(int fd, const FileSpec &file_spec, bool read,
     else if (read)
       m_arg = O_NOCTTY | O_RDONLY;
     else
-      m_arg = O_NOCTTY | O_CREAT | O_WRONLY;
+      m_arg = O_NOCTTY | O_CREAT | O_WRONLY | O_TRUNC;
     m_file_spec = file_spec;
     return true;
   } else {

lldb/test/API/commands/settings/TestSettings.py

@@ -528,6 +528,59 @@ def test_set_error_output_path(self):
             output, exe=False, startstr="This message should go to standard out."
         )
 
+    @skipIfDarwinEmbedded  # <rdar://problem/34446098> debugserver on ios etc can't write files
+    def test_same_error_output_path(self):
+        """Test that setting target.error and output-path to the same file path for the launched process works."""
+        self.build()
+
+        exe = self.getBuildArtifact("a.out")
+        self.runCmd("file " + exe, CURRENT_EXECUTABLE_SET)
+
+        # Set the error-path and output-path and verify both are set.
+        self.runCmd(
+            "settings set target.error-path '{0}'".format(
+                lldbutil.append_to_process_working_directory(self, "output.txt")
+            )
+        )
+        self.runCmd(
+            "settings set target.output-path '{0}".format(
+                lldbutil.append_to_process_working_directory(self, "output.txt")
+            )
+        )
+        # And add hooks to restore the original settings during tearDown().
+        self.addTearDownHook(lambda: self.runCmd("settings clear target.output-path"))
+        self.addTearDownHook(lambda: self.runCmd("settings clear target.error-path"))
+
+        self.expect(
+            "settings show target.error-path",
+            SETTING_MSG("target.error-path"),
+            substrs=["target.error-path (file)", 'output.txt"'],
+        )
+
+        self.expect(
+            "settings show target.output-path",
+            SETTING_MSG("target.output-path"),
+            substrs=["target.output-path (file)", 'output.txt"'],
+        )
+
+        self.runCmd(
+            "process launch --working-dir '{0}'".format(
+                self.get_process_working_directory()
+            ),
+            RUN_SUCCEEDED,
+        )
+
+        output = lldbutil.read_file_from_process_wd(self, "output.txt")
+        err_message = "This message should go to standard error."
+        out_message = "This message should go to standard out."
+        # Error msg should get flushed by the output msg
+        self.expect(output, exe=False, substrs=[out_message])
+        self.assertNotIn(
+            err_message,
+            output,
+            "Race condition when both stderr/stdout redirects to the same file",
+        )
+
     def test_print_dictionary_setting(self):
         self.runCmd("settings clear target.env-vars")
         self.runCmd('settings set target.env-vars ["MY_VAR"]=some-value')

lldb/test/API/python_api/process/io/TestProcessIO.py

@@ -95,6 +95,36 @@ def test_stdout_stderr_redirection(self):
         error = self.read_error_file_and_delete()
         self.check_process_output(output, error)
 
+    @skipIfWindows  # stdio manipulation unsupported on Windows
+    @expectedFlakeyLinux(bugnumber="llvm.org/pr26437")
+    @skipIfDarwinEmbedded  # debugserver can't create/write files on the device
+    def test_stdout_stderr_redirection_to_existing_files(self):
+        """Exercise SBLaunchInfo::AddOpenFileAction() for STDOUT and STDERR without redirecting STDIN to output files already exist."""
+        self.setup_test()
+        self.build()
+        self.create_target()
+        self.write_file_with_placeholder(self.output_file)
+        self.write_file_with_placeholder(self.error_file)
+        self.redirect_stdout()
+        self.redirect_stderr()
+        self.run_process(True)
+        output = self.read_output_file_and_delete()
+        error = self.read_error_file_and_delete()
+        self.check_process_output(output, error)
+
+    def write_file_with_placeholder(self, target_file):
+        placeholder = "This content should be overwritten."
+        if lldb.remote_platform:
+            self.runCmd(
+                'platform file write "{target}" -d "{data}"'.format(
+                    target=target_file, data=placeholder
+                )
+            )
+        else:
+            f = open(target_file, "w")
+            f.write(placeholder)
+            f.close()
+
     # target_file - path on local file system or remote file system if running remote
     # local_file - path on local system
     def read_file_and_delete(self, target_file, local_file):

lldb/unittests/Host/FileActionTest.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include <fcntl.h>
+
 #include "lldb/Host/FileAction.h"
 #include "gtest/gtest.h"
 
@@ -17,3 +19,26 @@ TEST(FileActionTest, Open) {
   EXPECT_EQ(Action.GetAction(), FileAction::eFileActionOpen);
   EXPECT_EQ(Action.GetFileSpec(), FileSpec("/tmp"));
 }
+
+TEST(FileActionTest, OpenReadWrite) {
+  FileAction Action;
+  Action.Open(48, FileSpec("/tmp_0"), /*read*/ true, /*write*/ true);
+  EXPECT_TRUE(Action.GetActionArgument() & (O_NOCTTY | O_CREAT | O_RDWR));
+  EXPECT_FALSE(Action.GetActionArgument() & O_RDONLY);
+  EXPECT_FALSE(Action.GetActionArgument() & O_WRONLY);
+}
+
+TEST(FileActionTest, OpenReadOnly) {
+  FileAction Action;
+  Action.Open(49, FileSpec("/tmp_1"), /*read*/ true, /*write*/ false);
+  EXPECT_TRUE(Action.GetActionArgument() & (O_NOCTTY | O_RDONLY));
+  EXPECT_FALSE(Action.GetActionArgument() & O_WRONLY);
+}
+
+TEST(FileActionTest, OpenWriteOnly) {
+  FileAction Action;
+  Action.Open(50, FileSpec("/tmp_2"), /*read*/ false, /*write*/ true);
+  EXPECT_TRUE(Action.GetActionArgument() &
+              (O_NOCTTY | O_CREAT | O_WRONLY | O_TRUNC));
+  EXPECT_FALSE(Action.GetActionArgument() & O_RDONLY);
+}

llvm/docs/ReleaseNotes.md

@@ -273,6 +273,8 @@ Changes to LLDB
 * LLDB can now read the `fpmr` register from AArch64 Linux processes and core
   files.
 
+* Program stdout/stderr redirection will now open the file with O_TRUNC flag, make sure to truncate the file if path already exists.
+  * eg. `settings set target.output-path/target.error-path <path/to/file>`
 
 Changes to BOLT
 ---------------------------------