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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
Date: Tue, 22 Oct 2019 03:57:09 -0500	[thread overview]
Message-ID: <20191022085709.GI28442@gate.crashing.org> (raw)
In-Reply-To: <20191022051529.GA44041@ubuntu-m2-xlarge-x86>

On Mon, Oct 21, 2019 at 10:15:29PM -0700, Nathan Chancellor wrote:
> On Fri, Oct 18, 2019 at 03:02:10PM -0500, Segher Boessenkool wrote:
> > I think the proper solution is for the kernel to *do* use -ffreestanding,
> > and then somehow tell the kernel that memcpy etc. are the standard
> > functions.  A freestanding GCC already requires memcpy, memmove, memset,
> > memcmp, and sometimes abort to exist and do the standard thing; why cannot
> > programs then also rely on it to be the standard functions.
> > 
> > What exact functions are the reason the kernel does not use -ffreestanding?
> > Is it just memcpy?  Is more wanted?
> 
> I think Linus summarized it pretty well here:
> 
> https://lore.kernel.org/lkml/CAHk-=wi-epJZfBHDbKKDZ64us7WkF=LpUfhvYBmZSteO8Q0RAg@mail.gmail.com/

GCC recognises __builtin_memcpy (or any other __builtin) just fine even
with -ffreestanding.

So the kernel wants a warning (or error) whenever a call to one of these
library functions is generated by the compiler without the user asking
for it directly (via a __builtin)?  And that is all that is needed for
the kernel to use -ffreestanding?

That shouldn't be hard.  Anything missing here?


Segher

  reply	other threads:[~2019-10-22  8:57 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-11 18:20 [PATCH v3 0/3] LLVM/Clang fixes for pseries_defconfig Nathan Chancellor
2019-09-11 18:20 ` [PATCH v3 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
2019-09-11 18:20 ` [PATCH v3 2/3] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
2019-09-11 20:55   ` Nick Desaulniers
2019-09-11 18:20 ` [PATCH v3 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
2019-09-11 21:01   ` Nick Desaulniers
2019-09-12  5:43     ` Nathan Chancellor
2019-09-12 17:30       ` Nick Desaulniers
2019-10-14  2:50 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nathan Chancellor
2019-10-14  2:50   ` [PATCH v4 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
2019-10-14  2:51   ` [PATCH v4 2/3] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
2019-10-14  2:51   ` [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
2019-10-14  9:35     ` Segher Boessenkool
2019-10-14 15:56       ` Nick Desaulniers
2019-10-14 19:11         ` Segher Boessenkool
2019-10-18 19:00           ` Nathan Chancellor
2019-10-18 20:02             ` Segher Boessenkool
2019-10-22  5:15               ` Nathan Chancellor
2019-10-22  8:57                 ` Segher Boessenkool [this message]
2019-10-30  4:12                   ` Nathan Chancellor
2019-10-14 16:03   ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nick Desaulniers
2019-11-19  4:57   ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nathan Chancellor
2019-11-19  4:57     ` [PATCH v5 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
2019-11-26  1:13       ` Michael Ellerman
2019-11-19  4:57     ` [PATCH v5 2/3] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
2019-11-19  4:57     ` [PATCH v5 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
2019-11-25 20:15     ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nick Desaulniers
2019-11-28  4:59       ` Michael Ellerman
2019-11-28  7:45         ` Nathan Chancellor

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