netdev - Re: [PATCH] tools bpftool: Fix json dump crash on powerpc

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Date:   Thu, 4 Jul 2019 13:42:10 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Michael Petlan <mpetlan@...hat.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH] tools bpftool: Fix json dump crash on powerpc

On Thu,  4 Jul 2019 10:58:56 +0200, Jiri Olsa wrote:
> Michael reported crash with by bpf program in json mode on powerpc:
> 
>   # bpftool prog -p dump jited id 14
>   [{
>         "name": "0xd00000000a9aa760",
>         "insns": [{
>                 "pc": "0x0",
>                 "operation": "nop",
>                 "operands": [null
>                 ]
>             },{
>                 "pc": "0x4",
>                 "operation": "nop",
>                 "operands": [null
>                 ]
>             },{
>                 "pc": "0x8",
>                 "operation": "mflr",
>   Segmentation fault (core dumped)
> 
> The code is assuming char pointers in format, which is not always
> true at least for powerpc. Fixing this by dumping the whole string
> into buffer based on its format.
> 
> Please note that libopcodes code does not check return values from
> fprintf callback, so there's no point to return error in case of
> allocation failure.

Well, it doesn't check it today, it may perhaps do it in the future?
Let's flip the question - since it doesn't check it today, why not
propagate the error? :)  We should stay close to how fprintf would
behave, IMHO.

Fixes: 107f041212c1 ("tools: bpftool: add JSON output for `bpftool prog dump jited *` command")

> Reported-by: Michael Petlan <mpetlan@...hat.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>