netdev - Re: [PATCH bpf-next v4 6/8] bpftool: Implement btfgen()

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Date:   Wed, 12 Jan 2022 18:09:23 +0000
From:   Quentin Monnet <quentin@...valent.com>
To:     Mauricio Vásquez <mauricio@...volk.io>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Rafael David Tinoco <rafaeldtinoco@...il.com>,
        Lorenzo Fontana <lorenzo.fontana@...stic.co>,
        Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v4 6/8] bpftool: Implement btfgen()

2022-01-12 09:27 UTC-0500 ~ Mauricio Vásquez <mauricio@...volk.io>
> btfgen() receives the path of a source and destination BTF files and a
> list of BPF objects. This function records the relocations for all
> objects and then generates the BTF file by calling btfgen_get_btf()
> (implemented in the following commits).
> 
> btfgen_record_obj() loads the BTF and BTF.ext sections of the BPF
> objects and loops through all CO-RE relocations. It uses
> bpf_core_calc_relo_insn() from libbpf and passes the target spec to
> btfgen_record_reloc() that saves the types involved in such relocation.
> 
> Signed-off-by: Mauricio Vásquez <mauricio@...volk.io>
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@...asec.com>
> Signed-off-by: Lorenzo Fontana <lorenzo.fontana@...stic.co>
> Signed-off-by: Leonardo Di Donato <leonardo.didonato@...stic.co>
> ---
>  tools/bpf/bpftool/gen.c | 221 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 219 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 905ab0ee6542..cef0ea99d4d9 100644

> +static int btfgen(const char *src_btf, const char *dst_btf, const char *objspaths[])
> +{
> +	struct btfgen_info *info;
> +	struct btf *btf_new = NULL;
> +	int err;
> +
> +	info = btfgen_new_info(src_btf);
> +	if (!info) {
> +		p_err("failed to allocate info structure: %s", strerror(errno));
> +		err = -errno;
> +		goto out;
> +	}
> +
> +	for (int i = 0; objspaths[i] != NULL; i++) {
> +		printf("OBJ : %s\n", objspaths[i]);

p_info()

> +
> +		err = btfgen_record_obj(info, objspaths[i]);
> +		if (err)
> +			goto out;
> +	}
> +
> +	btf_new = btfgen_get_btf(info);
> +	if (!btf_new) {
> +		err = -errno;
> +		p_err("error generating btf: %s", strerror(errno));
> +		goto out;
> +	}
> +
> +	printf("DBTF: %s\n", dst_btf);

p_info()