linux-kernel - Re: -fno-PIE, take #3

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Message-ID: <20161107063015.s7j6wpimj5himjp2@thunk.org>
Date:   Mon, 7 Nov 2016 01:30:15 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Michal Marek <mmarek@...e.com>,
        linux-kbuild@...r.kernel.org, x86@...nel.org,
        Al Viro <viro@...IV.linux.org.uk>,
        Ben Hutchings <ben@...adent.org.uk>,
        Sven Joachim <svenjoac@....de>,
        "Austin S. Hemmelgarn" <ahferroin7@...il.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: -fno-PIE, take #3

On Fri, Nov 04, 2016 at 07:39:37PM +0100, Sebastian Andrzej Siewior wrote:
> Debian gcc's is nowdays compiled with --enable-default-pie which means it does
> -fPIE by default. This breaks atleast x86-64 compiles.
> This is the third attempt to fix it, this time by using runtime detection of
> the -fno-PIE compiler switch (it was introduced in gcc 3.4, min required gcc is
> currently 3.2) so it can be backported to the stable kernels.
> As noted by Al this won't fix `git bisect' of stable kernels prio this commit.
> However using always a wrapper around gcc which adds -fno-PIE is not sollution
> I want to rely in future.

A wrapper around gcc which adds -fno-PIE doesn't work for the HOSTCC
builds, anyway:

% gcc -fno-PIE -o /tmp/hello /tmp/hello.c
/usr/bin/ld: /tmp/cckzDf9X.o: relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: Nonrepresentable section on output
collect2: error: ld returned 1 exit status

Alas, the only workaround I've found which doesn't involve bisecting
the kernel is to add "CC=gcc-5" to the Makefile invocation (assuming
gcc-5 is installed of course).

					- Ted