[gentoo-user] If I avaoided pic/PIC/pie; would it help/hurt?

[gentoo-user] If I avaoided pic/PIC/pie; would it help/hurt?

[Walter Dnes]

  I'm looking at going with...

CFLAGS="-O2 -march=native -mfpmath=sse -fomit-frame-pointer -pipe -fno-pic -fno-PIC -fno-pie -fno-unwind-tables -fno-asynchronous-unwind-tables"
CXXFLAGS="${CFLAGS}"

...and with -pic in USE.  This is the mirror image of the defaults.  Any
obvious problems, aside from losing a bit of security?  In case you're
wondering about the "pic" USE flag...

[d531][waltdnes][~] grep ":pic " /usr/portage/profiles/use.local.desc 
app-arch/gzip:pic - disable optimized assembly code that is not PIC friendly
app-benchmarks/ramspeed:pic - Force shared libraries to be built as PIC (this is slower)
app-emulation/open-vm-tools:pic - Force shared libraries to be built as PIC
dev-util/electron:pic - Disable optimized assembly code that is not PIC friendly
games-emulation/yabause:pic - disable optimized assembly code that is not PIC friendly
games-fps/duke3d:pic - disable optimized assembly code that is not PIC friendly
gnome-base/orbit:pic - Force libname-server-2 to be built as PIC; needed on hardened systems
media-libs/libpostproc:pic - Force shared libraries to be built as PIC (this is slower).
media-libs/mesa:pic - disable optimized assembly code that is not PIC friendly
media-libs/x264:pic - disable optimized assembly code that is not PIC friendly
media-libs/x265:pic - Disable optimized assembly code that is not PIC friendly
media-libs/xvid:pic - disable optimized assembly code that is not PIC friendly
media-video/ffmpeg:pic - Force shared libraries to be built as PIC (this is slower)
media-video/libav:pic - Force shared libraries to be built as PIC (this is slower).
media-video/transcode:pic - disable optimized assembly code that is not PIC friendly
www-client/chromium:pic - Disable optimized assembly code that is not PIC friendly

-- 
Walter Dnes <waltdnes@waltdnes.org>
I don't run "desktop environments"; I run useful applications

Re: [gentoo-user] If I avaoided pic/PIC/pie; would it help/hurt?

[Nils Holland]

On Tue, Dec 05, 2017 at 05:48:52PM -0500, Walter Dnes wrote:
>   I'm looking at going with...
> 
> CFLAGS="-O2 -march=native -mfpmath=sse -fomit-frame-pointer -pipe -fno-pic -fno-PIC -fno-pie -fno-unwind-tables -fno-asynchronous-unwind-tables"
> CXXFLAGS="${CFLAGS}"

Hmm ... is this really sufficient? In order to really not get a PIE
compiled, doesn't one also has to tell the linker about it? Testing on
a system that's already been upgraded to a GCC which produces PIEs by
default:

nils@boerne (GCC7) ~ $ gcc test.c
nils@boerne (GCC7) ~ $ file a.out
a.out: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, not stripped

-> As expected, this is a PIE ("ELF 32-bit LSB shared object").

ils@boerne (GCC7) ~ $ gcc -fno-pie test.c 
nils@boerne (GCC7) ~ $ file a.out 
a.out: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, not stripped

-> Despite "-fno-pie" being used, still a shared object / PIE.

ils@boerne (GCC7) ~ $ gcc -fno-pie -no-pie test.c
nils@boerne (GCC7) ~ $ file a.out
a.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, not stripped

-> Adding "-no-pie" to the game, and we get a normal "ELF 32-bit LSB
executable" (i.e. non-PIE).

So this might sound like you'd have to add "-no-pie" to your CFLAGS as
well, however, when I have a look at this bug report:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77464

I get the feeling that this is just asking for trouble.

Now, if I wanted to switch to a 17.0 profile, and still make sure
everything stays the way it was before PIE-wise (i.e. binaries get
compiled as non-PIE by default), I'd probably have a look instead at
overriding the "pie" USE flag that the new profile forces on GCC. It
should be able to set it to "-pie" in your local portage config. That
way, GCC should continue to be build with "--disable-default-pie",
which should make it emit normal non-PIE binaries by default, thus you
wouldn't have to specify anything PIE-related in your CFLAGS to
achieve just that. Might be the easier solution, I guess.

Greetings
Nils