[arch-dev-public] Changing compilation flags

Jan Alexander Steffens jan.steffens at gmail.com
Tue Dec 13 09:23:46 UTC 2016

On Mon, Oct 24, 2016 at 5:56 AM Allan McRae <allan at archlinux.org> wrote:

> Hi all,
> The results from the test-sec-flags [1] suite are in.  Many thanks to
> those that wrote this and those that submitted results.  I'm not going
> to list the summaries here, but the results show that at worst enabling
> a bunch of security flags in our packages will have a <1% impact on
> performance (and more likely a fraction of a percent).
> That means we will add all of these to our default CFLAGS/LDFLAGS etc.
> The changes are:
> 1) building gcc to enable PIE by default
> 2) add -z,now to LDFLAGS
> 3) and -fno-plt and -fstack-check to our CFLAGS
> Adding PIE means that programs get loaded at a random address,
> preventing an attacker from manipulating global data or hijacking
> control by reusing code.  Without this, ASLR is ineffective.  Enabling
> this by default in our compiler (there is a configure flag) means we
> will need to rebuild all packages with static libraries (which should be
> a fairly limited set).
> Adding -z,now to LDFLAGS disables lazy loading.  This means all function
> symbols are loaded at startup (with minor performance hit), but that
> means our RELRO support will make everything ro instead of some of the
> things.  Doing this enables us to use -fno-plt in our CFLAGS, which is a
> run-time optimisation allowing faster use of libraries.
> Adding -fstack-check to our CFLAGS guarantees stack overflows aren't
> exploitable.
> Note that any of these flags can be disabled in a PKGBUILD if really
> needed...  But if that is the case, bug reports should be filed.
> Given an assumed lack of objection, I will enable the build flags in our
> pacman.conf and rebuild gcc to enable pie and put them in [staging] at
> the end of this week (what better way to celebrate Halloween).  We will
> need a new devtools release then too.  Then the packages with static
> libraries will need rebuilt.
> After that, I would like to see [core] completely rebuilt, and audited
> to ensure our CFLAGS/LDFLAGS are actually being used in the build.
> Cheers,
> Allan

Will this affect i686 as well? According to this commit (
at least Ubuntu seems to have skipped that for now.

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