Re: [xz-devel] Re: xz-utils: make the selected POSIX shell stable accross build environments

[Ximin Luo]

+bugs-gnulib, reproducible-builds

Lasse Collin:
> On 2016-06-07 Ximin Luo wrote:
>> I've attached a patch that makes m4/posix-shell.m4 try constant paths
>> first. This should fix the issue.
>>
>> Upstream should also apply it - see more-stable-shell.patch.
> 
> Thanks!
> 
> posix-shell.m4 comes from gnulib so it would be nice if you could send
> the patch there and discuss the issue with gnulib developers. Perhaps
> there is a reason why the shells are tested in that order, although the
> gnulib commit messages don't have any reasoning. A guess is that
> someone might prefer if the same shell is used for running
> configure and the test suite scripts. Anyway, getting it fixed in gnulib
> would get it fixed in projects other than XZ Utils too.
> 

Thanks, yes this wasn't clear to me. We'd still need to contact projects that 
have already copied posix-shell.m4 into their source tree, but I suppose at 
least future projects will benefit.

bugs-gnulib, do you see any issue with this patch? The context is that some 
projects embed POSIX_SHELL into build products, so for build reproducibility it 
is better to have this detection script first try constant paths.

(Yes, if /bin/sh is not POSIX for one of the build machines, then we still have 
unreproducibility. But that's much less likely to happen. This is an "effort vs 
correctness" trade-off that I'm making.)

Regarding "someone might prefer if the same shell" as Lasse theorised, I'm not 
sure this will ever be an issue: if they prefer "the same shell", they would 
just use $SHELL or $CONFIG_SHELL instead of $POSIX_SHELL, so the only useful 
scenario is if somehow they wanted a shell that was POSIX-compatible but for 
some reason (I can't imagine why) needed this selection to favour 
$SHELL/$CONFIG_SHELL but still for it to be OK to fall back to the other 
constant values.

> One can force the POSIX shell to a specific value on the configure
> command line by passing, for example, "gl_cv_posix_shell=/bin/sh" as an
> argument. It's not documented in the --help output but it's mentioned
> in INSTALL section 3.1. That is an alternative to patching to get
> reproducible builds.
> 

Yeah, I saw that too, but thought this approach was a bit cleaner.

X

-- 
GPG: ed25519/56034877E1F87C35
GPG: rsa4096/1318EFAC5FBBDBCE
git://github.com/infinity0/pubkeys.git

more-stable-shell
Description: Text document