[llvm-dev] How data is laid out in default.profraw when doing profiling?

Eli Friedman via llvm-dev llvm-dev at lists.llvm.org
Thu May 16 11:43:54 PDT 2019

I would recommend reusing the existing code for writing those files, if possible. If atexit() doesn't work in your environment, you can still invoke the routines explicitly. https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#using-the-profiling-runtime-without-static-initializers describes this. 

If llvm-cov isn't working, the most likely cause is that there's something wrong with your ELF file.  Are you sure your ELF file matches the profile data, and has all the relevant __llvm_* sections?


> -----Original Message-----
> From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of xuruobin via
> llvm-dev
> Sent: Wednesday, May 15, 2019 8:27 PM
> To: llvm-dev at lists.llvm.org
> Cc: Yuchao (Michael) <michael.yuchao at huawei.com>
> Subject: [EXT] [llvm-dev] How data is laid out in default.profraw when doing
> profiling?
> Hi all,
>   I'm now working on llvm-cov for a new target and have a problem here.
>   Because of some reasons, users do not stub in the main function and  after
> running elf file, they cannot get a default profraw. Now they want to construct a
> default profraw manually but don't know how data is laid out in `default
> profraw` file.
>   We found a struct ProfDataIOVec in InstrProfilingWriter.c in compiler-rt and
> followed this layout.
> ```
>   ProfDataIOVec IOVec[] = {
>       {&Header, sizeof(__llvm_profile_header), 1},
>       {DataBegin, sizeof(__llvm_profile_data), DataSize},
>       {CountersBegin, sizeof(uint64_t), CountersSize},
>       {SkipNameDataWrite ? NULL : NamesBegin, sizeof(uint8_t), NamesSize},
>       {Zeroes, sizeof(uint8_t), Padding}};
> ```
>   This helped us successfully passed some small cases(not know for sure whether
> the coverage result is true, but we can see coverage report). But when we added
> more cases, `llvm-cov show -arch=xxx ...` gave us an assertion when entering
> fuction ` loadFunctionRecord ` in CoverageMapping.cpp. The OrigFuncName is
> empty when inserting into FunctionNames. Seems the llvm-cov cannot find a
> function name. I think it's because we didn't construct a correct default.profraw.
> So how data is laid out in default.profraw when doing profiling? Any help will be
> appreciated.
>   A small tip which may help. We are using coverage tool for a new target so
> when building compiler-rt, we use InstrProfilingPlatformOther.c
> Best,
> Ruobin
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