llvm-ar writing huge empty file?

[Lee Morgan]

Hi

llvm-ar appears to be writing a huge and empty file when trying to build a library.

strace reports thousands of 4k writes of blank strings and I can zip the eventual output from 8Gb to 8Mb. 

Does anyone know why this could be?

Thanks!

(on ubuntu 14.4)

./emsdk list

The following individual tools exist:

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           clang-incoming-64bit     

           clang-master-32bit       INSTALLED

    (*)    clang-master-64bit       INSTALLED

           emscripten-1.25.0         INSTALLED

           emscripten-1.27.0        

           emscripten-incoming      

    (*)    emscripten-master         INSTALLED

The following Emscripten SDK versions are available:

         sdk-incoming-32bit       

         sdk-incoming-64bit       

         sdk-master-32bit         INSTALLED

    *    sdk-master-64bit         INSTALLED

Items marked with * are activated for the current user.

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To access the historical archived versions, type 'emsdk list --old'

[Alon Zakai]

That sounds strange. The output library is bigger than the input files, and contains lots of empty space? Is it functional otherwise though?

Do you have a testcase that shows the problem?

- Alon

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[Jukka Jylänki]

By any chance, are you running under VirtualBox or other virtual VM? I remember some years ago running into an issue where a program would try to write to a shared directory tree under VirtualBox, and replacing writes turned into appending writes, causing innocent small writes to get amplified to several gigs. If so, does that happen if running outside a virtualized environment?

That's just a long shot, but your description reminded me of that issue I had.

[Lee Morgan]

Thanks I'm not using a VM.

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[Lee Morgan]

Actually I've found it happens with the freetype test case 'python tests/runner.py test_freetype' as this invokes the linker.

Again it quickly creates an 8gb file and writes empty strings. If left running it will eventually start appending - I haven't left it long enough to finish - although the appending makes me suspect it will just fill the disk.

I last tried with sdk-master-64bit but the incoming sdk has the same behaviour. I've left settings.js alone assuming 'emsdk install xxx' will overwrite it from the repo so it should be sensible defaults.

The /tmp where the temporary library file is created is on a partition with 12G free space.

I'm stumped on what would cause it though.

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[Lee Morgan]

Ok I found it - .a archive files only have 6 digits for user Ids and lvm-ar.cpp isnt properly checking for overflow causing huge padding characters to be written.

I generated a pull request although I don't know why this hasn't been a problem for someone before now.

Thanks.

[b...@dropbox.com]

I'm experiencing the same problem on 1.29, 528KB object file in 8GB+ file out. Where is the pull request you mentioned?

[b...@dropbox.com]

Nevermind - found it: https://github.com/kripken/emscripten-fastcomp/pull/59

[Lee Morgan]

There was a fix in llvm but that's not made it to emscripten latest yet. However it is in the incoming sdk so try that toolset.

I closed the pull request fix as it's already on its way.

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