linux-kernel - Re: undefined reference to `__aarch64_cas4

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Message-ID: <20240110141005.GL19790@gate.crashing.org>
Date: Wed, 10 Jan 2024 08:10:05 -0600
From: Segher Boessenkool <segher@...nel.crashing.org>
To: richard clark <richard.xnu.clark@...il.com>
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 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.

> 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