Messages in this thread | | | Date | Fri, 12 Mar 2021 14:24:47 -0800 | From | Fangrui Song <> | Subject | Re: [PATCH] gcov: fix clang-11+ support |
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On 2021-03-12, Nick Desaulniers wrote: >On Fri, Mar 12, 2021 at 12:25 PM 'Fangrui Song' via Clang Built Linux ><clang-built-linux@googlegroups.com> wrote: >> >> function_name can be unconditionally deleted. It is not used by llvm-cov >> gcov. You'll need to delete a few assignments to gcov_info_free but you >> can then unify the gcov_fn_info_dup and gcov_info_free implementations. >> >> LG. On big-endian systems, clang < 11 emitted .gcno/.gcda files do not >> work with llvm-cov gcov < 11. To fix it and make .gcno/.gcda work with >> gcc gcov I chose to break compatibility (and make all the breaking >> changes like deleting some CC1 options) in a short window. At that time >> I was not aware that there is the kernel implementation. Later on I was >> CCed on a few https://github.com/ClangBuiltLinux/linux/ gcov issues but >> I forgot to mention the interface change. > >These are all good suggestions. Since in v2 I'll drop support for >clang < 11, I will skip additional patches to disable GCOV when using >older clang for BE, and the function_name cleanup.
Only llvm_gcda_start_file & llvm_gcda_emit_function need version dispatch. In that case (since there will just be two #if in the file) we don't even need
depends on CC_IS_GCC || CLANG_VERSION >= 110000
>> Now in clang 11 onward, clang --coverage defaults to the gcov 4.8 >> compatible format. You can specify the CC1 option (internal option, >> subject to change) -coverage-version to make it compatible with other >> versions' gcov. >> >> -Xclang -coverage-version='407*' => 4.7 >> -Xclang -coverage-version='704*' => 7.4 >> -Xclang -coverage-version='B02*' => 10.2 (('B'-'A')*10 = 10) > >How come LLVM doesn't default to 10.2 format, if it can optionally >produce it? We might be able to reuse more code in the kernel between >the two impelementations, though I expect the symbols the runtime is >expected to provide will still differ. Seeing the `B` in `B02*` is >also curious. > >Thanks for the review, will include your tag in v2.
4.8 has the widest range of compiler support. gcov 4.8~7.* use the same format.
clang instrumentation does not support the column field (useless in my opinion) introduced in gcov 9, so it just writes zeros.
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