[llvm-dev] PGO, zlib and 'default.profraw'

[Justin Bogner via llvm-dev]

Can we improve the error message here? We should be able to check
zlib::isAvailable and give an error like "profile uses zlib compression
but the profile reader was built without zlib support" or so in this
case.

Xinliang David Li via llvm-dev <llvm-dev at lists.llvm.org> writes:
> The __llvm_prf_names section is compressed but your llvm-profdata tool is
> probably not built with zlib enabled.
>
> To disable compression, use option -mllvm -enable-name-compression=false
>  in your instrumentation build.
>
> David
>
> On Tue, Jul 18, 2017 at 7:05 AM, ORiordan, Martin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> We are trying to get PGO working for our embedded out-of-tree target, but
>> the utility ‘llvm-profdata’ does not like the data we are giving it.
>>
>>
>>
>> Because this is not a hosted environment, we have to off-chip the
>> profiling data ourselves, and although the data looks okay, ‘llvm-profdata’
>> reports the following error:
>>
>>
>>
>> *llvm-profdata show -all-functions -counts -detailed-summary -text
>> -static-func-full-module-prefix ~/Downloads/default.profraw*
>>
>> error: ~/Downloads/default.profraw: Failed to uncompress data (zlib)
>>
>>
>>
>> But even for a hosted system, it is not clear to me where ‘zlib’ gets
>> involved in compressing the data.  The start of our data looks like:
>>
>>
>>
>> *hexdump -C default.profraw*
>>
>> 00000000  81 52 66 6f 72 70 6c ff  04 00 00 00 00 00 00
>>
>> 00  |.Rforpl.........|
>>
>> 00000010  3c 00 00 00 00 00 00 00  28 01 00 00 00 00 00
>>
>> 00  |<.......(.......|
>>
>>
>>
>> Which looks valid for Little-Endian, 32-bit and LLVM v4.0.
>>
>>
>>
>> What do we need to do to prepare this raw data from the device into the
>> form that ‘llvm-profdata’ needs to see?
>>
>>
>>
>> Thanks,
>>
>>
>>
>>             MartinO
>>
>>
>>
>>
>>
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