Re: [PATCH] tools lib bpf: Use official ELF e_machine value

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Wang Nan <wangnan0@huawei.com>
Cc: acme@kernel.org, lizefan@huawei.com,
	linux-kernel@vger.kernel.org, pi3orama@163.com,
	Alexei Starovoitov <ast@kernel.org>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH] tools lib bpf: Use official ELF e_machine value
Date: Mon, 18 Jul 2016 14:37:00 -0700	[thread overview]
Message-ID: <20160718213658.GA44350@ast-mbp.thefacebook.com> (raw)
In-Reply-To: <1468821668-60088-1-git-send-email-wangnan0@huawei.com>

On Mon, Jul 18, 2016 at 06:01:08AM +0000, Wang Nan wrote:
> New LLVM will issue newly assigned EM_BPF machine code. The new code
> will be propogated to glibc and libelf.
> 
> This patch introduces the new machine code to libbpf.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Zefan Li <lizefan@huawei.com>
> Cc: pi3orama@163.com
> ---
>  tools/lib/bpf/libbpf.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 32e6b6b..b699aea 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -37,6 +37,10 @@
>  #include "libbpf.h"
>  #include "bpf.h"
>  
> +#ifndef EM_BPF
> +#define EM_BPF 247
> +#endif
> +
>  #define __printf(a, b)	__attribute__((format(printf, a, b)))
>  
>  __printf(1, 2)
> @@ -439,7 +443,8 @@ static int bpf_object__elf_init(struct bpf_object *obj)
>  	}
>  	ep = &obj->efile.ehdr;
>  
> -	if ((ep->e_type != ET_REL) || (ep->e_machine != 0)) {
> +	/* Old LLVM set e_machine to EM_NONE */
> +	if ((ep->e_type != ET_REL) || (ep->e_machine && (ep->e_machine != EM_BPF))) {

Thanks for the fix. Didn't realize we already check for zero here.
btw EM_BPF will be in llvm 3.9 release.

Acked-by: Alexei Starovoitov <ast@kernel.org>