linux-kernel - Re: [PATCH v2] samples/bpf: Add a workaround for asm

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Date:   Wed, 2 Oct 2019 13:22:08 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Florent Revest <revest@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Florent Revest <revest@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v2] samples/bpf: Add a workaround for asm_inline

On Wed, Oct 2, 2019 at 12:17 PM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> This was added in:
>
>   commit eb111869301e ("compiler-types.h: add asm_inline definition")
>
> and breaks samples/bpf as clang does not support asm __inline.
>
> Co-developed-by: Florent Revest <revest@...gle.com>
> Signed-off-by: Florent Revest <revest@...gle.com>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---
>
> Changes since v1:
>
> - Dropped the rename from asm_workaround.h to asm_goto_workaround.h
> - Dropped the fix for task_fd_query_user.c as it is updated in
>   https://lore.kernel.org/bpf/20191001112249.27341-1-bjorn.topel@gmail.com/
>
>  samples/bpf/asm_goto_workaround.h | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/samples/bpf/asm_goto_workaround.h b/samples/bpf/asm_goto_workaround.h
> index 7409722727ca..7048bb3594d6 100644
> --- a/samples/bpf/asm_goto_workaround.h
> +++ b/samples/bpf/asm_goto_workaround.h
> @@ -3,7 +3,8 @@
>  #ifndef __ASM_GOTO_WORKAROUND_H
>  #define __ASM_GOTO_WORKAROUND_H
>
> -/* this will bring in asm_volatile_goto macro definition
> +/*
> + * This will bring in asm_volatile_goto and asm_inline macro definitions
>   * if enabled by compiler and config options.
>   */
>  #include <linux/types.h>
> @@ -13,5 +14,15 @@
>  #define asm_volatile_goto(x...) asm volatile("invalid use of asm_volatile_goto")
>  #endif
>
> +/*
> + * asm_inline is defined as asm __inline in "include/linux/compiler_types.h"
> + * if supported by the kernel's CC (i.e CONFIG_CC_HAS_ASM_INLINE) which is not
> + * supported by CLANG.
> + */
> +#ifdef asm_inline
> +#undef asm_inline
> +#define asm_inline asm
> +#endif

Would it be better to just #undef CONFIG_CC_HAS_ASM_INLINE for BPF programs?

> +
>  #define volatile(x...) volatile("")
>  #endif
> --
> 2.20.1
>