bug#59365: make-dynamic-linker-cache OOMs for LLVM 15 on i686-linux

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi Ludovic,

Ludovic Courtès <ludo@gnu.org> writes:

> Hi,
>
> (Cc: Maxim and Greg for LLVM packaging questions below.)
>
> Marius Bakke <marius@gnu.org> skribis:
>
>> LLVM 15.0.4 fails on i686-linux:
>>
>>   https://ci.guix.gnu.org/build/1702995/details
>>
>> Because the 'make-dynamic-linker-cache' phase runs out of memory:
>>
>>   starting phase `make-dynamic-linker-cache'
>>   GC Warning: Repeated allocation of very large block (appr. size 268439552):
>> 	May lead to memory leak and poor performance
>>   GC Warning: Repeated allocation of very large block (appr. size 134221824):
>> 	May lead to memory leak and poor performance
>>   GC Warning: Repeated allocation of very large block (appr. size 268439552):
>>   	May lead to memory leak and poor performance
>>   GC Warning: Failed to expand heap by 285216768 bytes
>>   GC Warning: Failed to expand heap by 268439552 bytes
>>   GC Warning: Out of Memory! Heap size: 3620 MiB. Returning NULL!
>>   Warning: Unwind-only out of memory exception; skipping pre-unwind handler.
>>   Warning: Unwind-only out of memory exception; skipping pre-unwind handler.
>>   Warning: Unwind-only out of memory exception; skipping pre-unwind handler.
>>
>> (excerpt from https://ci.guix.gnu.org/build/1702995/log/raw)
>>
>> Not sure why this phase uses so much memory.  Ideas?
>
> Yes: the gremlin.scm code uses ‘file-dynamic-info’, which loads the
> whole file in memory.  Ridiculous.

If it loaded just that file, it should be fine, no?  It weighs 133 MiB,
as you've shown below:

> But the crux of the problem is that llvm@15 has a single huge shared
> library, unlike previous versions:
>
> $ du -hL  /gnu/store/bgqdvvi7k6l255332rfawgjmn2hpn13r-llvm-15.0.4/lib/*.so
> 133M    /gnu/store/bgqdvvi7k6l255332rfawgjmn2hpn13r-llvm-15.0.4/lib/libLLVM-15.0.4.so
> 96K     /gnu/store/bgqdvvi7k6l255332rfawgjmn2hpn13r-llvm-15.0.4/lib/libLTO.so
> 16K     /gnu/store/bgqdvvi7k6l255332rfawgjmn2hpn13r-llvm-15.0.4/lib/libRemarks.so
> (It also has tons of .a files, which shouldn’t be there.)

The static files are needed at least to build the clang runtime.  I had
tried to get rid of them without success.  Perhaps they could be moved
to a "static" output if they're needed only at that time.

> Is that big LLVM.so due to different build options on our side?  Or is
> it a radical upstream change (sounds unlikely, but who knows)?

It's caused by -DLLVM_LINK_LLVM_DYLIB=ON and -DLLVM_BUILD_LLVM_DYLIB=ON,
which is the supported configuration to build a shared library of LLVM
(-DBUILD_SHARED_LIBS=ON is obsolete/deprecated) [0].

It also makes things conveniently easy to link to LLVM; you just need to
link to '-lLLVM', and everything it needs is available.

[0]  https://llvm.org/docs/BuildingADistribution.html#special-notes-for-library-only-distributions

-- 
Thanks,
Maxim