netdev - Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

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Date:   Mon, 21 Oct 2019 16:16:00 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Andrii Nakryiko <andriin@...com>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

On Mon, 21 Oct 2019 16:02:27 +0200, Jiri Olsa wrote:
> > >  static int do_dump(int argc, char **argv)
> > >  {
> > >  	struct btf *btf = NULL;
> > > @@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
> > >  	__u32 btf_id = -1;
> > >  	const char *src;
> > >  	int fd = -1;
> > > -	int err;
> > > +	int err = 0;  
> > 
> > This change looks unnecessary.  
> 
> I'm getting confusing warnings from gcc about this,
> but there is a code path where do_dump would return
> untouched err:
> 
>   do_dump
>      int err;
> 
>      } else if (is_prefix(src, "file")) {
>        btf = btf__parse_elf(*argv, NULL);   // succeeds
> 
>      }
> 
>      while (argc) {
>        if (is_prefix(*argv, "format")) {
>        else {                                // in here
>           goto done;
>        }
> 
>      done:
>        return err;

ugh, right those look legit, although unrelated to you change.

err should always be set before jumping to 'done'. The error
setting in this function looks super messy :( Sometimes is returns
errno codes, sometimes positive values, sometimes negative, sometimes
just -1. Sometimes it jumps to 'done' for no good reason, ahh :/