Re: [PATCH 2/2] kbuild: add -fno-PIE

From: Austin S. Hemmelgarn
Date: Fri Nov 04 2016 - 07:37:40 EST

On 2016-11-03 21:08, Al Viro wrote:
On Thu, Nov 03, 2016 at 04:50:55PM -0600, Ben Hutchings wrote:
On Wed, 2016-11-02 at 18:20 +0100, Sebastian Andrzej Siewior wrote:
Debian started to build the gcc with -fPIE by default so the kernel
build ends before it starts properly with:
|kernel/bounds.c:1:0: error: code model kernel does not support PIC mode

Also add to KBUILD_AFLAGSi due to:

|gcc -Wp,-MD,arch/x86/entry/vdso/vdso32/.note.o.d â -mfentry -DCC_USING_FENTRY â vdso/vdso32/note.S
|arch/x86/entry/vdso/vdso32/note.S:1:0: sorry, unimplemented: -mfentry isnât supported for 32-bit in c ombination with -fpic

Unfortunately this isn't sufficient:

Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong available but compiler is broken
/build/linux-4.9~rc3/Makefile:1069: recipe for target 'prepare-compiler-check' failed
make[5]: *** [prepare-compiler-check] Error 1

scripts/ has its own list of options
which will need to include -fno-PIE.

That shit should be fixed in debian; no amount of kbuild changes will help
on bisect going back to a state prior to those. IOW, no matter what we
do kernel-side, that fuckup by doku, balint, needs to be fixed in
debian gcc package.

Al, seriously disappointed by that mess - debian gcc packagers are generally
clued enough to have known better. Reassigning bug reports in question
from gcc-6 to linux is beyond stupid; Balint is either being deliberately
obtuse, or geniunely unable to imagine that somebody might be using the
compiler _not_ for debian package builds.

If it helps, you could point out that Gentoo's hardened profile's GCC builds use PIE by default and have absolutely zero issues building the Linux kernel without any special kernel patches to turn it off (and has been doing so for years).