linux-kernel - Re: undefined reference to `__aarch64_cas4

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Message-ID: <ZZ_QaIrlKlFNdDbG@FVFF77S0Q05N>
Date: Thu, 11 Jan 2024 11:26:32 +0000
From: Mark Rutland <mark.rutland@....com>
To: richard clark <richard.xnu.clark@...il.com>
Cc: Segher Boessenkool <segher@...nel.crashing.org>,
	Xi Ruoyao <xry111@...111.site>, gcc-help@....gnu.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: undefined reference to `__aarch64_cas4_sync' error on arm64
 native build

On Thu, Jan 11, 2024 at 09:42:40AM +0800, richard clark wrote:
> On Wed, Jan 10, 2024 at 10:12 PM Segher Boessenkool
> <segher@...nel.crashing.org> wrote:
> >
> > On Wed, Jan 10, 2024 at 01:59:53PM +0800, richard clark wrote:
> > > A ported driver in linux kernel calls '__sync_val_compare_and_swap',
> >
> > That is a builtin function.  It does not necessarily expand to an actual
> > function call.  aarch64 will typically expand it to inline code.
> >
> native gcc version:
> gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
> cross-compiler gcc version:
> aarch64-linux-gnu-gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
> 
> Interesting, the same '__sync_val_compare_and_swap' in the .c file
> will be 'U __aarch64_cas4_sync' in the .o file compiled by native,
> will be 't __cmpxchg_case_mb_32' in the .o file compiled by
> aarch64-linux-gnu-gcc... don't know what the reason is

The __cmpxchg_case_mb_32() function is kernel code from
arch/arm64/include/asm/cmpxchg.h, so I do not believe that's being generated by
the compiler from __sync_val_compare_and_swap().

Are you certain that's being built from the exact same C file?

Are you able to share the code in question? Where has it come from in the first
place?

Thanks,
Mark.