[clang] fceaf86 - [clang] Fix UB when string.front() is used for the empty string

[Dmitry Polukhin via cfe-commits]

Author: Dmitry Polukhin
Date: 2021-06-30T01:07:47-07:00
New Revision: fceaf8621179aa758c44f3eaee02d789abfd455b

URL: https://github.com/llvm/llvm-project/commit/fceaf8621179aa758c44f3eaee02d789abfd455b
DIFF: https://github.com/llvm/llvm-project/commit/fceaf8621179aa758c44f3eaee02d789abfd455b.diff

LOG: [clang] Fix UB when string.front() is used for the empty string

Compilation database might have empty string as a command line argument.
But ExpandResponseFilesDatabase::expand doesn't expect this and assumes
that string.front() can be used for any argument. It is undefined behaviour if
string is empty. With debug build mode it causes crash in clangd.

Test Plan: check-clang

Differential Revision: https://reviews.llvm.org/D105120

Added: 
    

Modified: 
    clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
    clang/unittests/Tooling/CompilationDatabaseTest.cpp

Removed: 
    


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diff  --git a/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp b/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
index a825370afcf56..29787b8a88942 100644
--- a/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
+++ b/clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
@@ -54,7 +54,8 @@ class ExpandResponseFilesDatabase : public CompilationDatabase {
       Argv.reserve(Cmd.CommandLine.size());
       for (auto &Arg : Cmd.CommandLine) {
         Argv.push_back(Arg.c_str());
-        SeenRSPFile |= Arg.front() == '@';
+        if (!Arg.empty())
+          SeenRSPFile |= Arg.front() == '@';
       }
       if (!SeenRSPFile)
         continue;

diff  --git a/clang/unittests/Tooling/CompilationDatabaseTest.cpp b/clang/unittests/Tooling/CompilationDatabaseTest.cpp
index 9a04de32c852d..218a352f86f06 100644
--- a/clang/unittests/Tooling/CompilationDatabaseTest.cpp
+++ b/clang/unittests/Tooling/CompilationDatabaseTest.cpp
@@ -700,6 +700,10 @@ class MemDBTest : public ::testing::Test {
     SmallVector<StringRef, 8> Argv = {Clang, File, "-D", File};
     llvm::SplitString(Flags, Argv);
 
+    // Trim double quotation from the argumnets if any.
+    for (auto *It = Argv.begin(); It != Argv.end(); ++It)
+      *It = It->trim("\"");
+
     SmallString<32> Dir;
     llvm::sys::path::system_temp_directory(false, Dir);
 
@@ -962,5 +966,12 @@ TEST_F(ExpandResponseFilesTest, ExpandResponseFiles) {
   EXPECT_EQ(getCommand("bar.cpp"), "clang bar.cpp -D bar.cpp -Dflag");
 }
 
+TEST_F(ExpandResponseFilesTest, ExpandResponseFilesEmptyArgument) {
+  addFile(path(StringRef("rsp1.rsp")), "-Dflag");
+
+  add("foo.cpp", "clang", "@rsp1.rsp \"\"");
+  EXPECT_EQ(getCommand("foo.cpp"), "clang foo.cpp -D foo.cpp -Dflag ");
+}
+
 } // end namespace tooling
 } // end namespace clang