linux-kernel - Re: [PATCH] tools/lib/bpf: add pr

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Date:   Fri, 08 Dec 2023 00:58:02 +0200
From:   Eduard Zingerman <eddyz87@...il.com>
To:     Sergei Trofimovich <slyich@...il.com>, bpf@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH] tools/lib/bpf: add pr_warn() to more -EINVAL cases

On Thu, 2023-12-07 at 18:09 +0000, Sergei Trofimovich wrote:
> Before the change on `i686-linux` `systemd` build failed as:
> 
>     $ bpftool gen object src/core/bpf/socket_bind/socket-bind.bpf.o src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o
>     Error: failed to link 'src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o': Invalid argument (22)
> 
> After the change it fails as:
> 
>     $ bpftool gen object src/core/bpf/socket_bind/socket-bind.bpf.o src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o
>     libbpf: ELF section #9 has inconsistent alignment in src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o
>     Error: failed to link 'src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o': Invalid argument (22)
> 
> Now it's slightly easier to figure out what is wrong with an ELF file.

Hi Sergei,

Thank you for adding these prints.
Could you please make a few adjustments, as noted below.
Also, please add "libbpf:" prefix in subject and mention
linker_sanity_check_elf in it, e.g.:

  libbpf: add pr_warn() for EINVAL cases in linker_sanity_check_elf
  
or something like that.

[...]

> diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
> index 5ced96d99f8c..71bb4916b762 100644
> --- a/tools/lib/bpf/linker.c
> +++ b/tools/lib/bpf/linker.c
> @@ -719,13 +719,22 @@ static int linker_sanity_check_elf(struct src_obj *obj)
>  			return -EINVAL;
>  		}
>  
> -		if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign))
> +		if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign)) {
> +			pr_warn("ELF section #%zu alignment is non pow-of-2 alignment in %s\n",
> +				sec->sec_idx, obj->filename);

Could you please also print values for shdr->sh_addralign here?
And also print shdr->sh_addralign/data->d_align, shdr->sh_size/data->d_size
in corresponding pr_warn() calls below.

>  			return -EINVAL;
> -		if (sec->shdr->sh_addralign != sec->data->d_align)
> +		}
> +		if (sec->shdr->sh_addralign != sec->data->d_align) {
> +			pr_warn("ELF section #%zu has inconsistent alignment in %s\n",
> +				sec->sec_idx, obj->filename);
>  			return -EINVAL;
> +		}
>  
> -		if (sec->shdr->sh_size != sec->data->d_size)
> +		if (sec->shdr->sh_size != sec->data->d_size) {
> +			pr_warn("ELF section #%zu has inconsistent section size in %s\n",
> +				sec->sec_idx, obj->filename);
>  			return -EINVAL;
> +		}
>  
>  		switch (sec->shdr->sh_type) {
>  		case SHT_SYMTAB:

A few lines below this one there is:

		case SHT_PROGBITS:
			if (sec->shdr->sh_flags & SHF_EXECINSTR) {
				if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0)
					return -EINVAL;
			}
			break;

Could you please add pr_warn() there as well?