Re: -ffile-prefix-map option and reproducibility
Hi!
On Tue, 2023-02-07 at 16:41:47 +0100, Stéphane Glondu wrote:
> When building packages, a -ffile-prefix-map option is automatically injected
> into CFLAGS. Where does it come from? Since when?
This is coming from dpkg-buildflags (in this case probably indirectly
via debhelper). AFAICS it was added in dpkg 1.19.1 disabled by default,
and then switched to enabled by default in dpkg 1.20.6 (see #974087).
> I suspect this was added to improve reproducibility. Ironically, it makes
> packages that capture this variable non reproducible, since the build path
> seems to be randomized (has it always been the case? since when?). It is the
> case of OCaml (see #1030785), and seemingly of R as well (found by grepping
> in my /etc). I wouldn't be surprised other packages are affected as well.
AFAIR this was considered at the time, yes. If the flag is effectively
not fixing anything for the set of packages involved, and is in fact
actually making them unreproducible when they would not then, you can
disable the fixfilepath feature in the reproducible build flags area,
via DEB_BUILD_MAINT_OPTIONS. Perhaps even "globally" from a language
specific packaging helper or similar?
> Is there a way to not get this option? More elegant than explicitly
> filtering it out of CFLAGS in debian/rules...
See above.
I just noticed that several of these build flag features do not have
information in the man page about when they got first introduced, so
I'll be adding that in dpkg 1.22.x, once development opens up again.
Thanks,
Guillem
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