linux-kernel - Re: [PATCH] tools: bpf_jit_disasm: Add option to dump JIT image to a file.

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Date:   Tue, 11 Apr 2017 16:11:17 -0700
From:   David Daney <ddaney@...iumnetworks.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        David Daney <david.daney@...ium.com>,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tools: bpf_jit_disasm: Add option to dump JIT image to a
 file.

On 04/11/2017 02:54 PM, Daniel Borkmann wrote:
> On 04/11/2017 11:30 PM, David Daney wrote:
>> When debugging the JIT on an embedded platform or cross build
>> environment, libbfd may not be available, making it impossible to run
>> bpf_jit_disasm natively.
>>
>> Add an option to emit a binary image of the JIT code to a file.  This
>> file can then be disassembled off line.  Typical usage in this case
>> might be (pasting mips64 dmesg output to cat command):
>>
>>     $ cat > jit.raw
>>     $ bpf_jit_disasm -f jit.raw -O jit.bin
>>     $ mips64-linux-gnu-objdump -D -b binary -m mips:isa64r2 -EB jit.bin
>>
>> Signed-off-by: David Daney <david.daney@...ium.com>
>
> Seems good, we could at some point also add an -I jit.bin option
> if needed for offline analysis/comparison instead of using -f
> plain text.
>

FWIW:  The objdump incantation in the changelog does just about the same 
disassembly as the bpf_jit_disasm internal implementation.

> Thanks!
>
> Acked-by: Daniel Borkmann <daniel@...earbox.net>