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Re: gcc: -ftest-coverage and -auxbase


On Wed, Jun 12, 2019 at 10:17 PM <David.Taylor@dell.com> wrote:
>
> When doing a build, we use a pipe between GCC and GAS.
> And because we wish to do some analysis of the assembly code,
> we do not use -pipe but instead do '-S -c -'.  And this has worked
> fine for many years.

Can you please show us complete command-lines here?  -S -c -
will only assemble (and require source from standard input
and produce output in -.s).

> I was recently looking into collecting some coverage information.
> To that end, I added --coverage to the invocation line.  And it slowed
> things down by more than an order of magnitude!
>
> Investigating, it appears that the problem is the writing of the GCNO
> files.
>
> We do our builds on a build cluster with a lot of parallelism.
> With the result that a dozen machines are each doing a bunch
> of writes to the file '-.gcno' in an NFS mounted directory.
>
> Rather than have a full, not incremental, build take 5-10 minutes,
> It takes 4 hours.  And rather than have each of several thousand
> compiles produce their own GCNO file, they all get overwritten...
>
> Grep'ing around, I found '-auxbase'.  If I correctly understand it,
> when compiling
>
>     some/path/name.c
>
> into
>
>     bin/some-product/some/path/name.o,
>
> I could simply say
>
>     -auxbase $(@:%.o=%)
>
> The problem is that in common.opt, auxbase is marked RejectDriver.
>
> It looks like removing it would some my problem.  Anyone have a reason
> why removing that would be a bad idea?  Or have a different solution?
>
> Thanks.
>
> David


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