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Date:   Wed, 24 May 2023 15:28:46 +0200
From:   "Arnd Bergmann" <arnd@arndb.de>
To:     "Yonghong Song" <yhs@meta.com>, "Arnd Bergmann" <arnd@kernel.org>,
        "Alexei Starovoitov" <ast@kernel.org>,
        "Daniel Borkmann" <daniel@iogearbox.net>,
        "Andrii Nakryiko" <andrii@kernel.org>,
        "Song Liu" <song@kernel.org>,
        "Steven Rostedt" <rostedt@goodmis.org>,
        "Masami Hiramatsu" <mhiramat@kernel.org>
Cc:     stable@vger.kernel.org, "Martin KaFai Lau" <martin.lau@linux.dev>,
        "Yonghong Song" <yhs@fb.com>,
        "John Fastabend" <john.fastabend@gmail.com>,
        "KP Singh" <kpsingh@kernel.org>,
        "Stanislav Fomichev" <sdf@google.com>,
        "Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>,
        "Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
        "Dave Marchevsky" <davemarchevsky@fb.com>,
        "Joanne Koong" <joannelkoong@gmail.com>,
        "Delyan Kratunov" <delyank@fb.com>,
        "Peter Zijlstra" <peterz@infradead.org>, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] [v2] bpf: fix bpf_probe_read_kernel prototype mismatch
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On Wed, May 24, 2023, at 05:12, Yonghong Song wrote:
> On 5/23/23 12:43 PM, Arnd Bergmann wrote:

>> Aside from the warning, this addresses a bug on 32-bit architectures
>> from incorrect argument passing with the mismatched prototype.
>
> Could you explain what is this '32-bit architectures ... incorrect 
> argument passing' thing?

I've expanded that paragraph now:

| Aside from the warning, this addresses a bug on 32-bit architectures
| from incorrect argument passing with the mismatched prototype:
| BPF_CALL_x() functions use 64-bit arguments that are passed in
| pairs of register or on the stack on 32-bit architectures, while the
| normal function uses one register per argument.

Let me know if you think I should put more details in there.

>> @@ -1635,11 +1636,13 @@ bool bpf_opcode_in_insntable(u8 code)
>>   }
>>   
>>   #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>> -u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
>> +#ifndef CONFIG_BPF_EVENTS
>> +int bpf_probe_read_kernel_common(void * dst, u32 size, const void *unsafe_ptr)
>
> void * dst => void *dst
>

Fixed now.

Thanks,

     Arnd