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

[xuruobin via llvm-dev]

Hi Eli,

    For the first problem, I will try reuse the existing code.
    For the second problem that my llvm-cov isn't working, I compared elf file with original one(no -fprofile-instr-generate  -fcoverage-mapping flag). 5 new sections were introduced. __llvm_prf_names, __llvm_prf_cnts, __llvm_prf_data, __llvm_prf_vnds and __llvm_covmap. Does the sequence of 5 sections matter or are there more sections I need to use?

Best,
Ruobin

> -----Original Message-----
> From: Eli Friedman [mailto:efriedma at quicinc.com]
> Sent: Friday, May 17, 2019 2:44 AM
> To: xuruobin <xuruobin at huawei.com>; llvm-dev <llvm-dev at lists.llvm.org>
> Cc: Yuchao (Michael) <michael.yuchao at huawei.com>
> Subject: RE: [llvm-dev] How data is laid out in default.profraw when doing
> profiling?
> 
> 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?
> 
> -Eli
> 
> > -----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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