[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

[RFC] The PIE unholy mess


I'd like to get some feedback from porters and package maintainers,
given that this affects at least both groups. Some background first.

One of the reasons PIE has in the past not been enabled by default in
dpkg-buildflags, is because it introduced some slowness on some arches,
although this has somewhat changed recently. But also because
unconditionally setting it, breaks at least PIC builds. So PIE got
enabled recently by default in gcc, as it could easily control when it
is relevant. Although this has been done only for release architectures.

At about the same time this was being considered, I realized that dpkg
could enable this "safely" by using gcc specs files. But this is in
any case also required to be able to disable PIE when it is implicitly
enabled by default in gcc. So we'll need specs files no matter what,
at least for now.

While adapting dpkg-buildflags to cover for the new gcc defaults, I
unintentionally enabled PIE by default on all architectures, and when
I noticed, it seemed to make sense to leave it like that, because:

  * All previous build flags from dpkg-buildflags have always been
    enabled globally and only blacklisted completely when they have
    been non-functional.
  * It's a more consistent interface for packages, as they get built
    with the same flags everywhere. Otherwise we'd get PIE enabled by
    default in release arches, disabled by default elsewhere, and
    enabled or disabled depending on the package requesting so.
  * It will mean that PIE coverage reporting will be shadowed in
    lintian, because the tags only cover i386 and amd64, so maintainers
    will probably stop enabling them globally.

Matthias Klose recently filed an unclear report (#848129) on dpkg-dev
requesting to not enable PIE globally from dpkg-buildflags, and pretty
much immediately added a patch into gcc [P] to ignore dpkg-buildflags
not enable PIE explicitly (I only fully understood the request after
seeing the gcc patch).

  [P] <https://anonscm.debian.org/viewvc/gcccvs/branches/sid/gcc-6/debian/patches/ignore-pie-specs-when-not-enabled.diff?revision=9202&view=markup>

Besides this being completely broken, as DEB_BUILD_MAINT_OPTIONS
does not even need to be exported from debian/rules, nor from the
dpkg architecture.mk fragment, or when dpkg-buildflags is used with its
--export=configure or --export=cmdline. It's also a layer violation.
It also breaks unrelated stuff as now gcc emits notes when it thinks
the -specs option should not be passed. And while I could certainly
have started an arms-race by adding counter-measures by randomizing
the filenames or something similarly ugly, that'd be pretty much silly
and childish.

For better or worse, this does not affect the release architectures,
so by extension it should not affect the release, but it still sucks.

So, I'd like to know how people feel about the requested interface
(i.e. not enabling PIE globally from dpkg-buildflags). If there's
consensus that porters and maintainers want that, I'll just change
dpkg-buildflags to do this, even though I think it's a very
suboptiomal behavior.

Alternatively, porters could as well request PIE be enabled by default
in gcc on their port, which could make this also globally enabled.


Reply to: