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Date: Tue, 26 Feb 2019 17:02:00 -0000
From: Richard Biener <rguenther@suse.de>
To: Michael Matz <matz@suse.de>
cc: Mark Wielaard <mark@klomp.org>, gcc@gcc.gnu.org
Subject: Re: [RFC] Change PCH "checksum"
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On Tue, 26 Feb 2019, Michael Matz wrote:

> Hi,
> 
> On Tue, 26 Feb 2019, Richard Biener wrote:
> 
> > get_build_id_1 (struct dl_phdr_info *info, size_t, void *data)
> > { 
> 
> Isn't this all a bit silly?  We could simply encode the svn revision, or 
> maybe even just some random bytes generated once in stage1 at build time 
> as "checksum" and be done with.  In the latter case PCHs will then not 
> work across different compiler builds, but so what?

Yes, a random number would work for PCH purposes but of course not
for reproducible builds.  Somehow even compile-options are relevant
though so I'm not really sure how volatile the PCH format is.
That is, whether for example checksumming sources would work.

But yeah, I considered a --with-pch-checksum=XYZ to make this
configurable (where we could for example checksum the rpm
changes - iff PCHs of two different builds - say, one with checking
enabled and one with checking disabled - really interoperate).

Still, using the build-id looks so "obvious" ...

Richard.