[Lldb-commits] [lldb] 859052a - [lldb] Improve error message when we can't save core (#177496)

[via lldb-commits]

Author: Jonas Devlieghere
Date: 2026-01-22T22:32:03-08:00
New Revision: 859052a34ec5ad6c240366837fda12aa6801a560

URL: https://github.com/llvm/llvm-project/commit/859052a34ec5ad6c240366837fda12aa6801a560
DIFF: https://github.com/llvm/llvm-project/commit/859052a34ec5ad6c240366837fda12aa6801a560.diff

LOG: [lldb] Improve error message when we can't save core (#177496)

When you specify a filename to `process save core`, we'll write it in
the current working directory. In Xcode the CWD is `/` and you can't
generally write there.

```
(lldb) process save-core --style full foo
error: failed to save core file for process: Read-only file system
```

This PR improves the error message by including the output file when we
can't save core. However, just printing the filename isn't that much
more helpful, because FileSystem::Resolve only makes a path absolute if
it exists.

```
error: failed to save core file for process to 'foo': Read-only file system
```

Therefore I also modified the interface to add a flag to force resolve a
potentially non-exist path.

```
error: failed to save core file for process to '/foo': Read-only file system
```

Added: 
    

Modified: 
    lldb/include/lldb/Host/FileSystem.h
    lldb/source/Commands/CommandObjectProcess.cpp
    lldb/source/Host/common/FileSystem.cpp
    lldb/test/API/functionalities/process_save_core/TestProcessSaveCore.py

Removed: 
    


################################################################################
diff  --git a/lldb/include/lldb/Host/FileSystem.h b/lldb/include/lldb/Host/FileSystem.h
index 640f3846e448c..d0ac6edd2b286 100644
--- a/lldb/include/lldb/Host/FileSystem.h
+++ b/lldb/include/lldb/Host/FileSystem.h
@@ -137,9 +137,13 @@ class FileSystem {
   /// \}
 
   /// Resolve path to make it canonical.
+  ///
+  /// If force_make_absolute is specified, we'll make the path absolute even if
+  /// it does not exist.
   /// \{
-  void Resolve(llvm::SmallVectorImpl<char> &path);
-  void Resolve(FileSpec &file_spec);
+  void Resolve(llvm::SmallVectorImpl<char> &path,
+               bool force_make_absolute = false);
+  void Resolve(FileSpec &file_spec, bool force_make_absolute = false);
   /// \}
 
   /// Remove a single file.

diff  --git a/lldb/source/Commands/CommandObjectProcess.cpp b/lldb/source/Commands/CommandObjectProcess.cpp
index c17f12fae6e79..ca210e145d07e 100644
--- a/lldb/source/Commands/CommandObjectProcess.cpp
+++ b/lldb/source/Commands/CommandObjectProcess.cpp
@@ -1351,7 +1351,8 @@ class CommandObjectProcessSaveCore : public CommandObjectParsed {
     if (process_sp) {
       if (command.GetArgumentCount() == 1) {
         FileSpec output_file(command.GetArgumentAtIndex(0));
-        FileSystem::Instance().Resolve(output_file);
+        FileSystem::Instance().Resolve(output_file,
+                                       /*force_make_absolute=*/true);
         auto &core_dump_options = m_options.m_core_dump_options;
         core_dump_options.SetOutputFile(output_file);
         core_dump_options.SetProcess(process_sp);
@@ -1373,8 +1374,9 @@ class CommandObjectProcessSaveCore : public CommandObjectParsed {
           }
           result.SetStatus(eReturnStatusSuccessFinishResult);
         } else {
-          result.AppendErrorWithFormat(
-              "Failed to save core file for process: %s\n", error.AsCString());
+          result.AppendErrorWithFormatv(
+              "failed to save core file for process to '{0}': {1}\n",
+              output_file.GetPath(), error);
         }
       } else {
         result.AppendErrorWithFormat("'%s' takes one arguments:\nUsage: %s\n",

diff  --git a/lldb/source/Host/common/FileSystem.cpp b/lldb/source/Host/common/FileSystem.cpp
index 00919fe9a574d..5ca3b3640ce5f 100644
--- a/lldb/source/Host/common/FileSystem.cpp
+++ b/lldb/source/Host/common/FileSystem.cpp
@@ -222,7 +222,8 @@ std::error_code FileSystem::GetRealPath(const Twine &path,
   return m_fs->getRealPath(path, output);
 }
 
-void FileSystem::Resolve(SmallVectorImpl<char> &path) {
+void FileSystem::Resolve(SmallVectorImpl<char> &path,
+                         bool force_make_absolute) {
   if (path.empty())
     return;
 
@@ -237,14 +238,14 @@ void FileSystem::Resolve(SmallVectorImpl<char> &path) {
   MakeAbsolute(absolute);
 
   path.clear();
-  if (Exists(absolute)) {
+  if (force_make_absolute || Exists(absolute)) {
     path.append(absolute.begin(), absolute.end());
   } else {
     path.append(resolved.begin(), resolved.end());
   }
 }
 
-void FileSystem::Resolve(FileSpec &file_spec) {
+void FileSystem::Resolve(FileSpec &file_spec, bool force_make_absolute) {
   if (!file_spec)
     return;
 
@@ -253,7 +254,7 @@ void FileSystem::Resolve(FileSpec &file_spec) {
   file_spec.GetPath(path);
 
   // Resolve the path.
-  Resolve(path);
+  Resolve(path, force_make_absolute);
 
   // Update the FileSpec with the resolved path.
   if (file_spec.GetFilename().IsEmpty())

diff  --git a/lldb/test/API/functionalities/process_save_core/TestProcessSaveCore.py b/lldb/test/API/functionalities/process_save_core/TestProcessSaveCore.py
index cf7bd9787d649..98f143f15471b 100644
--- a/lldb/test/API/functionalities/process_save_core/TestProcessSaveCore.py
+++ b/lldb/test/API/functionalities/process_save_core/TestProcessSaveCore.py
@@ -4,6 +4,8 @@
 
 import os
 import lldb
+import tempfile
+import stat
 from lldbsuite.test.decorators import *
 from lldbsuite.test.lldbtest import *
 from lldbsuite.test import lldbutil
@@ -106,3 +108,30 @@ def test_help(self):
                 "stack",
             ],
         )
+
+    @skipIfRemote
+    def test_save_core_to_nonwritable_dir(self):
+        """Test that saving a core file to a non-writable directory produces a helpful error message."""
+        self.build()
+        exe = self.getBuildArtifact("a.out")
+
+        # Create a non-writable temporary directory.
+        temp_dir = tempfile.mkdtemp()
+        os.chmod(temp_dir, stat.S_IRUSR | stat.S_IXUSR)
+        self.addTearDownHook(lambda: os.rmdir(temp_dir))
+
+        target = self.dbg.CreateTarget(exe)
+        breakpoint = target.BreakpointCreateByName("bar")
+        process = target.LaunchSimple(None, None, self.get_process_working_directory())
+        self.assertState(process.GetState(), lldb.eStateStopped)
+
+        # Try to save a core file to the non-writable directory.
+        core_file = os.path.join(temp_dir, "core")
+        self.expect(
+            f"process save-core {core_file}",
+            error=True,
+            substrs=[
+                "failed to save core file for process to",
+                os.path.join(temp_dir, "core"),
+            ],
+        )