[lldb] Fix an asan error from 27df2d9

This error is caused by a combination of a couple of factors:
- the test accidentally creating a list with a single (empty) FileSpec
  instead of an empty list
- lldb overzeleously converting empty strings into nullptrs
- asan overzeleously validating symlink(2) arguments (the real symlink
  call would just fail with EFAULT)

I fix this by using FileSpec::GetPath instead of GetCString. This avoids
the nullptr and also avoids inserting the path into the global string
pool.

I also enhance the test case to test both empty paths and empty lists.

Author: labath

lldb/packages/Python/lldbsuite/test/functionalities/breakpoint/comp_dir_symlink/TestCompDirSymLink.py

@@ -46,6 +46,18 @@ def test_symlink_paths_set_procselfcwd(self):
 
     @skipIf(hostoslist=["windows"])
     def test_symlink_paths_unset(self):
+        pwd_symlink = self.create_src_symlink()
+        self.doBuild(pwd_symlink, None)
+        src_path = self.getBuildArtifact(_SRC_FILE)
+        self.assertRaises(
+            AssertionError,
+            lldbutil.run_break_set_by_file_and_line,
+            self,
+            src_path,
+            self.line)
+
+    @skipIf(hostoslist=["windows"])
+    def test_symlink_paths_empty(self):
         pwd_symlink = self.create_src_symlink()
         self.doBuild(pwd_symlink, "")
         src_path = self.getBuildArtifact(_SRC_FILE)
@@ -67,9 +79,11 @@ def create_src_symlink(self):
     def doBuild(self, pwd_symlink, setting_value):
         self.build(None, None, {'PWD': pwd_symlink})
 
-        self.runCmd(
-            "settings set %s '%s'" %
-            (_COMP_DIR_SYM_LINK_PROP, setting_value))
+        if setting_value:
+            cmd = "settings set %s '%s'" % (_COMP_DIR_SYM_LINK_PROP, setting_value)
+        else:
+            cmd = "settings clear %s"%_COMP_DIR_SYM_LINK_PROP
+        self.runCmd(cmd)
 
         exe = self.getBuildArtifact(_EXE_NAME)
         self.runCmd('file ' + exe, CURRENT_EXECUTABLE_SET)

lldb/source/Host/posix/FileSystemPosix.cpp

@@ -43,7 +43,7 @@ Status FileSystem::Symlink(const FileSpec &src, const FileSpec &dst) {
 Status FileSystem::Readlink(const FileSpec &src, FileSpec &dst) {
   Status error;
   char buf[PATH_MAX];
-  ssize_t count = ::readlink(src.GetCString(), buf, sizeof(buf) - 1);
+  ssize_t count = ::readlink(src.GetPath().c_str(), buf, sizeof(buf) - 1);
   if (count < 0)
     error.SetErrorToErrno();
   else {