[lfs-support] Use of gcc plugins in the kernel and entropy

[Pierre Labastie]

Hi list,

FWIW, the script 'scripts/gcc-plugin.sh', in the kernel tree
returns an error on Debian, if gcc-8-plugin-dev is not installed.
This results in HAVE_GCC_PLUGIN to be set to 'n', so that the
configuration step does not ask about (or show) the GCC plugin
menu.

The main result for me was that I got an error when compiling
the kernel during an LFS build, using a .config file generated
on Debian: on LFS, all gcc files are installed, and
HAVE_GCC_PLUGIN gets set to 'y' in this case. So now the
config step asks about GCC plugins, which is not defined
in .config (neither 'not set' nor 'y')and 'make oldconfig'
fails...

But I wanted also to mention that there seem to be a lot of
plugins about randomization and entropy. Maybe their
presence (or absence) might explain
Ken's difficulties (thread starting at
http://lists.linuxfromscratch.org/pipermail/blfs-support/2018-June/080154.html)
(or not)...

Regards
Pierre
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[Ken Moffat]

Post by Pierre Labastie
Hi list,
But I wanted also to mention that there seem to be a lot of
plugins about randomization and entropy. Maybe their
presence (or absence) might explain
Ken's difficulties (thread starting at
http://lists.linuxfromscratch.org/pipermail/blfs-support/2018-June/080154.html)
(or not)...

Hi Pierre,

according to Documentation/gcc-plugins.txt:

GCC plugins are loadable modules that provide extra features to the
compiler [1]_. They are useful for runtime instrumentation and static
analysis. We can analyse, change and add further code during
compilation via callbacks [2]_, GIMPLE [3]_, IPA [4]_ and RTL passes
[5]_.

(snipped the rest, and the references).

So, it is something for kernel developers. My issue seems to be due
to unspecified changes in the kernel's calculation of entropy (and
variations probably made bisection unreliable). I've accepted that
I'll need haveged on (at least) the low-end AMD box without an RNG,
and for the moment I'm now building it on all desktops. For 4.19 I
should be able to decide to trust the machine's RNG on those with
low entropy. For servers, at the moment no idea - my test server
build has a single spinning rust drive, seems ok for entropy with
the latest stable kernel (4.14.67) on 8.3.

ĸen
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