netdev - Re: [PATCHv2] bpftool: Try to read btf as raw data if elf read fails

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Message-ID: <20191025163228.GB10170@krava>
Date:   Fri, 25 Oct 2019 18:32:28 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Andrii Nakryiko <andriin@...com>, Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Yonghong Song <yhs@...com>, Martin Lau <kafai@...com>,
        "andrii.nakryiko@...il.com" <andrii.nakryiko@...il.com>
Subject: Re: [PATCHv2] bpftool: Try to read btf as raw data if elf read fails

On Fri, Oct 25, 2019 at 09:31:16AM -0700, Jakub Kicinski wrote:
> On Fri, 25 Oct 2019 05:01:17 +0000, Andrii Nakryiko wrote:
> > >> +static bool is_btf_raw(const char *file)
> > >> +{
> > >> +	__u16 magic = 0;
> > >> +	int fd;
> > >> +
> > >> +	fd = open(file, O_RDONLY);
> > >> +	if (fd < 0)
> > >> +		return false;
> > >> +
> > >> +	read(fd, &magic, sizeof(magic));
> > >> +	close(fd);
> > >> +	return magic == BTF_MAGIC;  
> > > 
> > > Isn't it suspicious to read() 2 bytes into an u16 and compare to a
> > > constant like endianness doesn't matter? Quick grep doesn't reveal
> > > BTF_MAGIC being endian-aware..  
> > 
> > Right now we support only loading BTF in native endianness, so I think 
> > this should do. If we ever add ability to load non-native endianness, 
> > then we'll have to adjust this.
> 
> This doesn't do native endianness, this does LE-only. It will not work
> on BE machines.

hum, let me try.. I thought it would

jirka