linux-kernel - Re: [PATCH] powerpc: vdso: fix building with wrong-endian toolchain

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Date: Fri, 7 Jun 2024 10:41:33 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Michael Ellerman <mpe@...erman.id.au>
Cc: Arnd Bergmann <arnd@...nel.org>, Nicolas Schier <nicolas@...sle.eu>,
        Arnd Bergmann <arnd@...db.de>, linux-kbuild@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>, linux-kernel@...r.kernel.org,
        Nicholas Piggin <npiggin@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc: vdso: fix building with wrong-endian toolchain

On Fri, Jun 07, 2024 at 10:42:44PM +1000, Michael Ellerman wrote:
> I use the korg toolchains every day, and kisskb uses them too.
> 
> What commit / defconfig are you seeing the errors with?
> 
> Is it just the 12.3.0 toolchain or all of them? I just tested 12.3.0
> here and it built OK.
> 
> I guess you're building on x86 or arm64? I build on ppc64le, I wonder if
> that makes a difference.

The core problem of course is pre-processing a linker script with the
C preprocessor (although linker scripts themselves have much more
capable facilities for this), and by doing this as-if it was a piece of
assembler code that for some strange reason you want fed through the C
preprocessor (as .S file).

What is it the C preprocessor is wanted for here?  Is there nothing
better that can be done?

> The patch is probably OK regardless, but I'd rather understand what the
> actual problem is.

Yeah.  The problem was found later in the thread (the CPP env var, or
shell var anyway, not sure what it is here) was set.  Fun and
surprising!  If you do nnot like such fun all that much, reduce the
surface of eternal surprise?  (I don't like saying "attack surface", but
that is what it is as well).

Segher