Currently, with -fsanitize=address, the driver appends libclang_rt.asan.a to

the link command. This all works fine when the driver is also responsible for
adding -lstdc++ to the link command. But, if -lstdc++ (or libstdc++.a, etc) is
passed explicitly to the driver, the ASan runtime will appear in the link
command after the standard library, leading to multiple-definition errors for
the global 'operator new' and 'operator delete'. Fix this in a painfully
simple way, by inserting libclang_rt.asan.a at the start of the link command
instead of the end.

If we need to do something more clever, we can walk the link command looking
for something that resembles libstdc++ and insert libclang_rt.asan.a as late
as possible, but the simple solution works for now.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169310 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index ab00118244..92f41063e2 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1512,7 +1512,7 @@ static void addAsanRTLinux(const ToolChain &TC, const ArgList &Args,
     llvm::sys::path::append(LibAsan, "lib", "linux",
         (Twine("libclang_rt.asan-") +
             TC.getArchName() + "-android.so"));
-    CmdArgs.push_back(Args.MakeArgString(LibAsan));
+    CmdArgs.insert(CmdArgs.begin(), Args.MakeArgString(LibAsan));
   } else {
     if (!Args.hasArg(options::OPT_shared)) {
       // LibAsan is "libclang_rt.asan-<ArchName>.a" in the Linux library
@@ -1521,7 +1521,11 @@ static void addAsanRTLinux(const ToolChain &TC, const ArgList &Args,
       llvm::sys::path::append(LibAsan, "lib", "linux",
                               (Twine("libclang_rt.asan-") +
                                TC.getArchName() + ".a"));
-      CmdArgs.push_back(Args.MakeArgString(LibAsan));
+      // The ASan runtime needs to come before -lstdc++ (or -lc++, libstdc++.a,
+      // etc.) so that the linker picks ASan's versions of the global 'operator
+      // new' and 'operator delete' symbols. We take the extreme (but simple)
+      // strategy of inserting it at the front of the link command.
+      CmdArgs.insert(CmdArgs.begin(), Args.MakeArgString(LibAsan));
       CmdArgs.push_back("-lpthread");
       CmdArgs.push_back("-ldl");
       CmdArgs.push_back("-export-dynamic");