linux-kernel - Re: [PATCH v1 2/5] powerpc/32: Don't always pass -mcpu=powerpc to the compiler

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 11 Jul 2022 11:50:53 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Pali Rohár <pali@...nel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v1 2/5] powerpc/32: Don't always pass -mcpu=powerpc to the compiler

On Mon, Jul 11, 2022 at 04:19:30PM +0200, Christophe Leroy wrote:
> Since commit 4bf4f42a2feb ("powerpc/kbuild: Set default generic
> machine type for 32-bit compile"), when building a 32 bits kernel
> with a bi-arch version of GCC, or when building a book3s/32 kernel,
> the option -mcpu=powerpc is passed to GCC at all time, relying on it
> being eventually overriden by a subsequent -mcpu=xxxx.
> 
> But when building the same kernel with a 32 bits only version of GCC,
> that is not done, relying on gcc being built with the expected default
> CPU.
> 
> This logic has two problems. First, it is a bit fragile to rely on
> whether the GCC version is bi-arch or not, because today we can have
> bi-arch versions of GCC configured with a 32 bits default. Second,
> there are some versions of GCC which don't support -mcpu=powerpc,
> for instance for e500 SPE-only versions.

More fundamentally, the *only* thing you should check biarch for is
for determining if you can use both -m32 and -m64 with the same
compiler.  Everything behaves identically in a biarch and a non-biarch
compiler, other than the latter screams bloody murder if you try to
change the architecture from 32 to 64 bit or vice versa.

> So, stop relying on this approximative logic and allow the user to
> decide whether he/she wants to use the toolchain's default CPU or if
> he/she wants to set one, and allow only possible CPUs based on the
> selected target.
> 
> Reported-by: Pali Rohár <pali@...nel.org>
> Tested-by: Pali Rohár <pali@...nel.org>
> Reviewed-by: Arnd Bergmann <arnd@...db.de>
> Cc: Segher Boessenkool <segher@...nel.crashing.org>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

Reviewed-by: Segher Boessenkool <segher@...nel.crashing.org>

Looks good to me.  This untangles/demystifies quite some code :-)


Segher