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toolchain/40972: add support to ar for 'deterministic mode'



>Number:         40972
>Category:       toolchain
>Synopsis:       add support to ar for 'deterministic mode'
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    toolchain-manager
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 06 08:00:00 +0000 2009
>Originator:     Chris Demetriou
>Release:        NetBSD-current sources as of 2009-03-05
>Organization:
Toolchain Hackers 'r' Us
>Environment:
irrelevant
>Description:
It's useful for 'ar' to support a deterministic mode of operation, in which ar 
uses well-known uids, gids, timestamps, file modes, etc., when creating 
archives.  This allows rebuilds to produce identical .a files.

I've wanted this feature for a while, and I know Perry has too.

The best way I've found to use this to build 'random' software is to create two 
shell scripts:
 * a wrapper for 'ar' which adds the 'D' flag into the options, and
 * a wrapper for 'ranlib' which is just #!/bin/true

(if people call ranlib to update the archive map timestamp, that'll screw up 
the nice determinism.)  For use in building NetBSD, it should be sufficient to 
just set 'D' in the system makefiles' ar flags where appropriate, and stub out 
uses of ranlib.

I coded the attached patch up based on NetBSD's gnu/dist/binutils sources as of 
the evening (US/Pacific) 2009-03-05.  I'm putting the uuencoded bzip2'd patch 
in the 'fix' section, below.  (Let me know if you run into problems decoding 
it.)
>How-To-Repeat:
ar cv archive1.a obj1.o obj2.o
sleep 5
touch obj1.o obj2.o
ar cv archive2.a obj1.o obj2.o
cmp -l archive1.a archive2.a

lame!
>Fix:
begin 644 netbsd_deterministic_archives.patch.bz2
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`
end



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