linux-kernel - Re: undefined reference to `__aarch64_cas4

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Date: Thu, 11 Jan 2024 09:42:40 +0800
From: richard clark <richard.xnu.clark@...il.com>
To: Segher Boessenkool <segher@...nel.crashing.org>
Cc: Xi Ruoyao <xry111@...111.site>, Mark Rutland <mark.rutland@....com>, 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 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 cross-compiler 'aarch64-linux-gnu-gcc' doesn't complain
> > '__aarch64_cas1_sync' undefined reference, but the native compiler
> > will complain. As Mark mentioned, I double check that both cross and
> > native compiler should have  ''-moutline-atomics' option enabled, do
> > you know the reason for that?
>
> Ah, so you are requesting external functions.
>
> I am no aarch64 expert, but apparently there were some problems in
> GCC 11, maybe that is what you saw?  Or with some distros, anyway.
>
> It also matters if you have ARMv8.1-A enabled, the LSE instructions.
>
> Open a GCC bug report if you have more details?  Thanks,
>
>
> Segher