netdev - Re: [PATCH bpf-next v3 10/10] tools: bpftool: add delimiters to multi-function JITed dumps

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Date:   Wed, 23 May 2018 19:29:08 +0530
From:   Sandipan Das <sandipan@...ux.vnet.ibm.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Jakub Kicinski <jakub.kicinski@...ronome.com>, ast@...nel.org,
        netdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        mpe@...erman.id.au, naveen.n.rao@...ux.vnet.ibm.com,
        Quentin Monnet <quentin.monnet@...ronome.com>
Subject: Re: [PATCH bpf-next v3 10/10] tools: bpftool: add delimiters to
 multi-function JITed dumps


On 05/23/2018 07:20 PM, Daniel Borkmann wrote:
> On 05/23/2018 12:37 PM, Sandipan Das wrote:
> [...]
>> Other than that, for powerpc64, there is a problem with the way the
>> binutils disassembler code (in "opcodes/ppc-dis.c") passes arguments
>> to the callback fprintf_json().
>>
>> In fprintf_json(), we always expect the va_list elements to resolve
>> to strings (char *). But for powerpc64, the register or immediate
>> operands are always passed as integers. So, when the code attempts
>> to resolve these operands using va_arg(ap, char *), bpftool crashes.
>> For now, I am using a workaround based on vsnprintf() but this does
>> not get the semantics correct for memory operands. You can probably
>> see that for the store instructions in the JSON dump above this.
>>
>> Daniel,
>>
>> Would it be okay if I send out a fix for this in a different series?
> 
> I'm fine either way with regards to the fix. Feels like a portability bug
> in the binutils disassembler?
> 
> We could probably have a feature test like in test-disassembler-four-args
> and select a workaround in bpftool based on that outcome.
> 
> Thanks Sandipan!
> 
>   [1] tools/build/feature/test-disassembler-four-args.c
> 

Cool. Thanks for the tip!

- Sandipan