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

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Message-ID: <E7A6B893-9E4B-4C22-A0CC-833AF45AF460@fb.com>
Date:   Wed, 2 Oct 2019 21:05:12 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     KP Singh <kpsingh@...omium.org>,
        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 Lau" <kafai@...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 Oct 2, 2019, at 1:22 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> 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?

I guess that is still useful when gcc fully support BPF?

Thanks,
Song