[Driver] Avoid invalidated iterator in insertTargetAndModeArgs

Doing an .insert() can potentially invalidate iterators by reallocating the
vector's storage. When all the stars align just right, this causes segfaults
or glibc aborts.

Gentoo Linux bug (crashes while building Chromium): https://bugs.gentoo.org/650082.

Patch by Hector Martin!

Differential Revision: https://reviews.llvm.org/D44607

llvm-svn: 327863

1 files changed, 5 insertions, 4 deletions

diff --git a/clang/tools/driver/driver.cpp b/clang/tools/driver/driver.cpp
index 611bff233e4..72d56a72873 100644
--- a/clang/tools/driver/driver.cpp
+++ b/clang/tools/driver/driver.cpp
@@ -212,20 +212,21 @@ static void insertTargetAndModeArgs(const ParsedClangName &NameParts,
   // Put target and mode arguments at the start of argument list so that
   // arguments specified in command line could override them. Avoid putting
   // them at index 0, as an option like '-cc1' must remain the first.
-  auto InsertionPoint = ArgVector.begin();
-  if (InsertionPoint != ArgVector.end())
+  int InsertionPoint = 0;
+  if (ArgVector.size() > 0)
     ++InsertionPoint;
 
   if (NameParts.DriverMode) {
     // Add the mode flag to the arguments.
-    ArgVector.insert(InsertionPoint,
+    ArgVector.insert(ArgVector.begin() + InsertionPoint,
                      GetStableCStr(SavedStrings, NameParts.DriverMode));
   }
 
   if (NameParts.TargetIsValid) {
     const char *arr[] = {"-target", GetStableCStr(SavedStrings,
                                                   NameParts.TargetPrefix)};
-    ArgVector.insert(InsertionPoint, std::begin(arr), std::end(arr));
+    ArgVector.insert(ArgVector.begin() + InsertionPoint,
+                     std::begin(arr), std::end(arr));
   }
 }