linux-kernel - Re: undefined reference to `__aarch64_cas4

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Message-ID: <ZZb2f0U4qTWDjCGj@FVFF77S0Q05N.cambridge.arm.com>
Date: Thu, 4 Jan 2024 18:18:39 +0000
From: Mark Rutland <mark.rutland@....com>
To: richard clark <richard.xnu.clark@...il.com>
Cc: 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 Tue, Jan 02, 2024 at 04:53:53PM +0800, richard clark wrote:
> Ah, the driver is trying to use the native gcc built atomic ops like:
> __sync_val_compare_and_swap, but it seems the native aarch64 doesn't
> provide these builtin atomic primitives while they are in the cross
> compile toolchain.
> The issue can be resolved by replacing the
> **__sync_val_compare_and_swap** with **atomic_cmpxchg**.

Yup, that's the right thing to do; drivers *shouldn't* use the builtins
directly, and *should* use the kernel's native atomic*() API.

> But don't know why the native aarch64 toolchain doesn't have those
> builtin atomic functions...

I suspect this is down to your toolchain enabling -moutline-atomics by default;
that expands the builtins into calls to out-of-line functions. I suspect your
cross-compile toolchain doesn't enable that by default.

As above, since nothing should be using the builtins, we don't implement
out-of-line versions nor do we override the option.

Mark.

> On Tue, Jan 2, 2024 at 11:29 AM richard clark
> <richard.xnu.clark@...il.com> wrote:
> >
> > Hi,
> >
> > I have a strong power arm64 box, and the linux distro is ubuntu 22.04,
> > the native gcc version is:
> >
> > $ gcc --version
> > gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
> > Copyright (C) 2021 Free Software Foundation, Inc.
> > This is free software; see the source for copying conditions.  There is NO
> > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> >
> > It will abort the kernel build with the complaint by 'make Image':
> > ld: Unexpected GOT/PLT entries detected!
> > ld: Unexpected run-time procedure linkages detected!
> > ld: ID map text too big or misaligned
> > ld: drivers/net/nvidia_eth.o: in function `osi_lock_irq_enabled':
> > osi_hal.c:(.text+0x3cc): undefined reference to `__aarch64_cas4_sync'
> > ...
> >
> > But the cross-compile with aarch64-linux-gnu-gcc on the x86 box
> > doesn't show the above error message.
> > Any comments/suggestions? Thanks very much!
> >
> > Richard
>