linux-kernel - Re: linux-next: build warning after merge of Linus' tree

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Message-ID: <CAHk-=wjsMVpEvwq=+wAx20RWe_25LDoiMd34Msd4Mrww_-Z3Fw@mail.gmail.com>
Date: Tue, 22 Apr 2025 08:59:00 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: build warning after merge of Linus' tree

On Tue, 22 Apr 2025 at 03:47, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>
> These builds were done with a gcc 11.1.0 cross compiler.

That sounds like there might be some issue with the cross-compiler
logic somewhere, because the Makefile logic is using the standard

    KBUILD_CFLAGS += $(call cc-option, xyzzy)

pattern.  We literally have seven other occurrences of that same logic
just in that same Makefile above it (and many more in other
makefiles).

IOW, it's *supposed* to only actually use the flag if the compiler
supports it, so having the compiler then say "I don't recognize that
option" is kind of odd. We've explicitly tested that the compiler
supports it.

Does the warning happen for all files that get built, or just some
specific ones? I wonder if we have some issue where we end up using
two different compilers (I'd assume native and cross-built), and we
use KBUILD_CFLAGS for the wrong compiler (or we use cc-option with the
wrong compiler, but I'd expect that to affect *everything* - that
'cc-option' thing is not some kind of unusual pattern).

It may be that the other options we check for have been around for so
long that they just don't show the issue (ie the 'cc-option' for the
other cases may also be using the wrong compiler, but then it's hidden
by the fact that both compiler versions just happen to support all the
other options anyway).

                    Linus