linux-kernel - Re: [PATCH v2] powerpc: fix EDEADLOCK redefinition error in uapi/asm/errno.h

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Date:   Thu, 17 Sep 2020 21:55:04 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Tony Ambardar <tony.ambardar@...il.com>
Cc:     Tony Ambardar <Tony.Ambardar@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, Rosen Penev <rosenp@...il.com>,
        linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2] powerpc: fix EDEADLOCK redefinition error in uapi/asm/errno.h

[ Cc += linux-arch & Arnd ]

Hi Tony,

This looks OK to me, but I'm always a bit nervous about changes in uapi.
I've Cc'ed linux-arch and Arnd who look after the asm-generic headers,
which this is slightly related to, just in case.

One minor comment below.

Tony Ambardar <tony.ambardar@...il.com> writes:
> A few archs like powerpc have different errno.h values for macros
> EDEADLOCK and EDEADLK. In code including both libc and linux versions of
> errno.h, this can result in multiple definitions of EDEADLOCK in the
> include chain. Definitions to the same value (e.g. seen with mips) do
> not raise warnings, but on powerpc there are redefinitions changing the
> value, which raise warnings and errors (if using "-Werror").
>
> Guard against these redefinitions to avoid build errors like the following,
> first seen cross-compiling libbpf v5.8.9 for powerpc using GCC 8.4.0 with
> musl 1.1.24:
>
>   In file included from ../../arch/powerpc/include/uapi/asm/errno.h:5,
>                    from ../../include/linux/err.h:8,
>                    from libbpf.c:29:
>   ../../include/uapi/asm-generic/errno.h:40: error: "EDEADLOCK" redefined [-Werror]
>    #define EDEADLOCK EDEADLK
>
>   In file included from toolchain-powerpc_8540_gcc-8.4.0_musl/include/errno.h:10,
>                    from libbpf.c:26:
>   toolchain-powerpc_8540_gcc-8.4.0_musl/include/bits/errno.h:58: note: this is the location of the previous definition
>    #define EDEADLOCK       58
>
>   cc1: all warnings being treated as errors
>
> Fixes: 95f28190aa01 ("tools include arch: Grab a copy of errno.h for arch's supported by perf")
> Fixes: c3617f72036c ("UAPI: (Scripted) Disintegrate arch/powerpc/include/asm")

I suspect that's not the right commit to tag. It just moved errno.h from
arch/powerpc/include/asm to arch/powerpc/include/uapi/asm. It's content
was almost identical, and entirely identical as far as EDEADLOCK was
concerned.

Prior to that the file lived in asm-powerpc/errno.h, eg:

$ git cat-file -p b8b572e1015f^:include/asm-powerpc/errno.h

Before that it was include/asm-ppc64/errno.h, content still the same.

To go back further we'd have to look at the historical git trees, which
is probably overkill. I'm pretty sure it's always had this problem.

So we should probably drop the Fixes tags and just Cc: stable, that
means please backport it as far back as possible.

cheers


> Reported-by: Rosen Penev <rosenp@...il.com>
> Signed-off-by: Tony Ambardar <Tony.Ambardar@...il.com>
> ---
> v1 -> v2:
>  * clean up commit description formatting
> ---
>  arch/powerpc/include/uapi/asm/errno.h       | 1 +
>  tools/arch/powerpc/include/uapi/asm/errno.h | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/include/uapi/asm/errno.h b/arch/powerpc/include/uapi/asm/errno.h
> index cc79856896a1..4ba87de32be0 100644
> --- a/arch/powerpc/include/uapi/asm/errno.h
> +++ b/arch/powerpc/include/uapi/asm/errno.h
> @@ -2,6 +2,7 @@
>  #ifndef _ASM_POWERPC_ERRNO_H
>  #define _ASM_POWERPC_ERRNO_H
>  
> +#undef	EDEADLOCK
>  #include <asm-generic/errno.h>
>  
>  #undef	EDEADLOCK
> diff --git a/tools/arch/powerpc/include/uapi/asm/errno.h b/tools/arch/powerpc/include/uapi/asm/errno.h
> index cc79856896a1..4ba87de32be0 100644
> --- a/tools/arch/powerpc/include/uapi/asm/errno.h
> +++ b/tools/arch/powerpc/include/uapi/asm/errno.h
> @@ -2,6 +2,7 @@
>  #ifndef _ASM_POWERPC_ERRNO_H
>  #define _ASM_POWERPC_ERRNO_H
>  
> +#undef	EDEADLOCK
>  #include <asm-generic/errno.h>
>  
>  #undef	EDEADLOCK
> -- 
> 2.25.1