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Re: [RFC] Change PCH "checksum"


On February 22, 2019 5:03:46 PM GMT+01:00, Jakub Jelinek <jakub@redhat.com> wrote:
>On Fri, Feb 22, 2019 at 08:47:09AM -0700, Jeff Law wrote:
>> > 2019-02-22  Richard Biener  <rguenther@suse.de>
>> > 
>> > 	c/
>> > 	* Make-lang.in (cc1-checksum.c): Checksum only gtype-desc.o.
>> > 
>> > 	cp/
>> > 	* Make-lang.in (cc1plus-checksum.c): Checksum only gtype-desc.o.
>> > 
>> > 	objc/
>> > 	* Make-lang.in (cc1obj-checksum.c): Checksum only gtype-desc.o.
>> > 
>> > 	objcp/
>> > 	* Make-lang.in (cc1objplus-checksum.c): Checksum only
>gtype-desc.o.
>> ISTM that gtype-desc effectively describes the structure of all the
>GC data.
>> 
>> Given we're summing the thin-archives, we're already missing things
>like
>> a change in static data.  So I don't think your patch is a
>degradation
>> over the current state.  I'm not 100% sure the current state is
>correct
>> though :-)
>
>Does it cover everything though?  I believe gtype-desc.c only covers a
>small
>portion, the rest is in all the gtype-*.h and gt-*.h headers that are
>included in the various object files.
>So, either we need to checksum all the object files that include gt-*.h
>or
>gtype-*.h headers in addition to gtype-desc.o, or perhaps checksum
>gtype.state ?  Though, that state wouldn't cover changes in ABI etc.

Gtype-desc.o does not cover everything indeed. But the current state doesn't cover Gtype-desc.o... Slightly better would be to Re-include frontend objects. 

Not sure why we checksummed build flags for example. Isn't it enough to handle gty walking changes?

Anyway, for suse I'm probably using the build-id thing. 

Richard. 

>	Jakub


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