[LLVMdev] Non-deterministic builds

[Erik Cederstrand]

Hello LLVM'ers

I have noticed that two consecutive builds of clang, clang++ and tblgen don't produce identical binaries (as in md5 sums) on identical source code (I'm on FreeBSD). I ran strings(1) on the two clang binaries, and I get the following:

248400,248403c248400,248403
< N128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_36FAEB5D11PreVerifierE
< N128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_36FAEB5D8VerifierE
< N4llvm11InstVisitorIN128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_36FAEB5D8VerifierEvEE
< N128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_36FAEB5D7TypeSetE
---
> N128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_95F4F51B11PreVerifierE
> N128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_95F4F51B8VerifierE
> N4llvm11InstVisitorIN128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_95F4F51B8VerifierEvEE
> N128_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Verifier.cpp_00000000_95F4F51B7TypeSetE
248735,248736c248735,248736
< N135_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_PrintModulePass.cpp_00000000_E8B12D4D15PrintModulePassE
< N135_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_PrintModulePass.cpp_00000000_E8B12D4D17PrintFunctionPassE
---
> N135_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_PrintModulePass.cpp_00000000_BDCFB9C615PrintModulePassE
> N135_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_PrintModulePass.cpp_00000000_BDCFB9C617PrintFunctionPassE
248855c248855
< N131_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_PassManager.cpp_00000000_B138034413BBPassManagerE
---
> N131_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_PassManager.cpp_00000000_9C5AE4C313BBPassManagerE
249398c249398
< N124_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Pass.cpp_00000000_16144DA716GetCFGOnlyPassesE
---
> N124_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmcore_.._.._.._contrib_llvm_lib_VMCore_Pass.cpp_00000000_6C67211416GetCFGOnlyPassesE
251862c251862
< N4llvm3sys11ThreadLocalIKN144_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmsupport_.._.._.._contrib_llvm_lib_Support_CrashRecoveryContext.cpp_00000000_BFDB511124CrashRecoveryContextImplEEE
---
> N4llvm3sys11ThreadLocalIKN144_GLOBAL__N__usr_home_erik_freebsd_head_src_lib_clang_libllvmsupport_.._.._.._contrib_llvm_lib_Support_CrashRecoveryContext.cpp_00000000_A7307A7424CrashRecoveryContextImplEEE


clang++ and tblgen produce similar diffs.

I'm trying to build a system to detect the actual binary impact on specific commits to FreeBSD, so things like this is noise for me. Also, things like running ccache on top of clang is a lot easier if ccache can just use the checksum of /usr/bin/clang to verify that it can use the cache.

Would it be possible to unify the above output as to create deterministic builds of clang, clang++ and tblgen?

I believe the binaries are created with binutils-as and binutils-ld, if it matters.

Thanks,
Erik Cederstrand
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