[CFI] Compilation error in Windows

[llvmbot]

Bugzilla Link	41779
Version	8.0
OS	Windows NT
Attachments	A C++ program that makes function calls through function pointers
Reporter	LLVM Bugzilla Contributor
CC	@efriedma-quic,@rnk

Extended Description

I was testing LLVM Control Flow Integrity (CFI) on x64 Windows 10. The c++ source code attached makes a function call through a function pointer in an intensive loop. Which function will be called is based on the parity of a random integer. With CFI enabled (using flags -fsanitize=cfi and -flto), such function calls should be compiled to indirect calls. This works perfectly in Linux, but I got a compilation error in Windows using the same command:

C:\Users\Xiaoyang\Dropbox\CFIBenchmarks\fptr>clang++ -fsanitize=cfi -flto -o fptr.exe fptr.cpp
C:\Users\Xiaoyang\AppData\Local\Temp\fptr-3c8ec9.o : fatal error LNK1107: invalid or corrupt file: cannot read at 0x1CB0
clang++.exe: error: linker command failed with exit code 1107 (use -v to see invocation)

If I remove the CFI and link-time optimization flags, I can successfully compile and run this program:

C:\Users\Xiaoyang\Dropbox\CFIBenchmarks\fptr>clang++ fptr.cpp -o fptr.exe
C:\Users\Xiaoyang\Dropbox\CFIBenchmarks\fptr>fptr.exe
49893 odd numbers
50107 even numbers

I got this error in both LLVM 8.0.0 and 7.0.1.

[efriedma-quic]

It looks like clang is trying to perform LTO using link.exe, which is never going to work. The Microsoft linker doesn't support plugins like binutils.

"-fuse-ld=lld-link" should get you past that error. I guess it's a clang driver bug that -flto doesn't imply that.

Not sure if you'll run into any other issues.