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Subject: Re: [PATCH bpf-next] riscv, bpf: fix some compiler error
To:     =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn.topel@gmail.com>
References: <20211102145642.724820-1-tongtiangen@huawei.com>
 <CAJ+HfNg1Ki=1Zc+ThW-ynvtDo5=fNAUK-XV08-icz-nY9CNoUQ@mail.gmail.com>
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CC:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Palmer Dabbelt <palmerdabbelt@google.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
From:   tongtiangen <tongtiangen@huawei.com>
Message-ID: <f3ed7e48-c565-9147-eca0-6298a36b3d61@huawei.com>
Date:   Wed, 3 Nov 2021 15:26:48 +0800
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On 2021/11/3 14:10, Björn Töpel wrote:
> On Wed, 3 Nov 2021 at 04:06, tongtiangen <tongtiangen@huawei.com> wrote:
>>
> [...]
>>>
>> Hi Björn:
>>  From the perspective of development, introduce asm/extable.h is also prepare for the
>> subsequent modification of exception_table_entry, such as:
>>    1. https://lkml.org/lkml/2021/10/20/591
>>    2. https://lore.kernel.org/linux-arm-kernel/20211019160219.5202-11-mark.rutland@arm.com/
>>
>> Therefore, the prototype declarations and definitions related to kernel config are placed in head file,
>> which can avoid compiler error and simplify the rendering of functions.
>>
>
> Sure, but *this* patch is about getting the broken RV32 build to work,
> aimed for the bpf tree. Moving the extable.h is unrelated, and should
> not be done here. IMO it would be better to have this patch small/easy
> to read. I can't really see how this patch helps, when merging with
> Jisheng's work.
>
> ...and I still think that:
> --8<--
> diff --git a/arch/riscv/mm/extable.c b/arch/riscv/mm/extable.c
> index 18bf338303b6..ddb7d3b99e89 100644
> --- a/arch/riscv/mm/extable.c
> +++ b/arch/riscv/mm/extable.c
> @@ -11,7 +11,7 @@
>  #include <linux/module.h>
>  #include <linux/uaccess.h>
>
> -#ifdef CONFIG_BPF_JIT
> +#if defined(CONFIG_BPF_JIT) && defined(CONFIG_ARCH_RV64I)
>  int rv_bpf_fixup_exception(const struct exception_table_entry *ex,
> struct pt_regs *regs);
>  #endif
>
> @@ -23,7 +23,7 @@ int fixup_exception(struct pt_regs *regs)
>         if (!fixup)
>                 return 0;
>
> -#ifdef CONFIG_BPF_JIT
> +#if defined(CONFIG_BPF_JIT) && defined(CONFIG_ARCH_RV64I)
>         if (regs->epc >= BPF_JIT_REGION_START && regs->epc < BPF_JIT_REGION_END)
>                 return rv_bpf_fixup_exception(fixup, regs);
>  #endif
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 2ca345c7b0bf..6372a235522d 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -459,6 +459,8 @@ static int emit_call(bool fixed, u64 addr, struct
> rv_jit_context *ctx)
>  #define BPF_FIXUP_OFFSET_MASK   GENMASK(26, 0)
>  #define BPF_FIXUP_REG_MASK      GENMASK(31, 27)
>
> +int rv_bpf_fixup_exception(const struct exception_table_entry *ex,
> +                          struct pt_regs *regs);
>  int rv_bpf_fixup_exception(const struct exception_table_entry *ex,
>                                 struct pt_regs *regs)
>  {
> -->8--
>
> is much simpler.

Adding a function declaration in bpf_jit_comp64.c file cannot fix this compiler error:

....
when CONFIG_BPF_JIT and CONFIG_ARCH_64I is open, There is the following compiler error (W=1):
   error: no previous prototype for 'rv_bpf_fixup_exception'
....

To fix this compiler error, you need to make a declaration in a header file, which is also
the reason for introducing extable.h.

Before making this patch, I thought about this change, but on the whole, I think the modification
scheme of adding header files moved me.;-)

>
>
>
> Thoughts?
> Björn
>
>
>
>
>> Thanks.
>> Tong.
>>
>>>
>>> Björn
>>> .
>>>
> .
>