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 15:50:33 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Sandipan Das <sandipan@...ux.vnet.ibm.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     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 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