[LLVMdev] Proposal: release MDNodes for source modules (LTO+debug info)

[Stephen Checkoway]

On Nov 15, 2013, at 10:19 AM, Rafael Espíndola <rafael.espindola at gmail.com> wrote:

> On 14 November 2013 18:01, Stephen Checkoway <s at pahtak.org> wrote:
>> 
>> On Nov 14, 2013, at 8:19 AM, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
>> 
>>> But gold has at most 2 objects loaded at any time.
>> 
>> Are you sure about that? I haven't looked into it but while building Chromium with LTO, I get:
>> 
>> ../../third_party/gold/gold64: fatal error: out of file descriptors and couldn't close any
>> clang: error: linker command failed with exit code 1 (use -v to see invocation)
>> ninja: build stopped: subcommand failed.
>> [secdev:~/chromium/src/out/Release] (master) s$ ulimit -Sn
>> 10000
>> 
>> Looking in /proc, it has 10013 open file descriptors. With only 2 objects loaded at a time, I'd expect many fewer file descriptors to be open. Maybe it only has 2 objects in memory at once but keeps all the file descriptors open?
> 
> That is odd. I will debug it in a sec, but we have in the claim_file_hook:
> 
>  if (code_gen) {
>    if (lto_codegen_add_module(code_gen, M)) {
>      (*message)(LDPL_ERROR, "Error linking module: %s",
>                 lto_get_error_message());
>      return LDPS_ERR;
>    }
>  }
> 
>  lto_module_dispose(M);
> 
> In fact, with current gold we call get_view, so the plugin uses the
> same fd as gold. It might actually be a bug with gold trying to cache
> too many open files.
> 
> How are you trying to build it?

The standard Chromium build system was modified to add -flto -Os to cflags (which I'm assuming in this case also gets passed to clang++) and -flto to ldflags in chromium/src/build/common.gypi and I think some of the build files for libraries that are built along with Chromium were modified to not use -flto because they didn't work. I'm not the one who did that work, unfortunately, so I can't say for sure exactly what all was modified.

-- 
Stephen Checkoway