Re: [PATCH bpf-next v4 5/8] libbpf: Support opening bpf objects of either endianness

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On Fri, Aug 30, 2024 at 12:30 AM Tony Ambardar <tony.ambardar@xxxxxxxxx> wrote:
>
> Allow bpf_object__open() to access files of either endianness, and convert
> included BPF programs to native byte-order in-memory for introspection.
> Loading BPF objects of non-native byte-order is still disallowed however.
>
> Signed-off-by: Tony Ambardar <tony.ambardar@xxxxxxxxx>
> ---
>  tools/lib/bpf/libbpf.c          | 49 +++++++++++++++++++++++++++------
>  tools/lib/bpf/libbpf_internal.h | 11 ++++++++
>  2 files changed, 52 insertions(+), 8 deletions(-)
>

[...]

>
> +       /* Validate ELF object endianness... */
> +       if (ehdr->e_ident[EI_DATA] != ELFDATA2LSB &&
> +           ehdr->e_ident[EI_DATA] != ELFDATA2MSB) {
> +               err = -LIBBPF_ERRNO__ENDIAN;
> +               pr_warn("elf: '%s' has unknown byte order\n", obj->path);
> +               goto errout;
> +       }
> +       /* and preserve outside lifetime of bpf_object_open() */

what does it mean "preserve outside lifetime" ?

> +       obj->byteorder = ehdr->e_ident[EI_DATA];
> +
> +
> +

why so many empty lines?..

>         if (elf_getshdrstrndx(elf, &obj->efile.shstrndx)) {
>                 pr_warn("elf: failed to get section names section index for %s: %s\n",
>                         obj->path, elf_errmsg(-1));

[...]

>         err = bpf_object__elf_init(obj);
> -       err = err ? : bpf_object__check_endianness(obj);
>         err = err ? : bpf_object__elf_collect(obj);
>         err = err ? : bpf_object__collect_externs(obj);
>         err = err ? : bpf_object_fixup_btf(obj);
> @@ -8500,6 +8529,10 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
>
>         if (obj->gen_loader)
>                 bpf_gen__init(obj->gen_loader, extra_log_level, obj->nr_programs, obj->nr_maps);

nit: add {} around if, both sides should either have or not have {}

> +       else if (!is_native_endianness(obj)) {
> +               pr_warn("object '%s' is not native endianness\n", obj->name);

"object '%s': load is not supported in non-native endianness\n"


> +               return libbpf_err(-LIBBPF_ERRNO__ENDIAN);
> +       }
>
>         err = bpf_object_prepare_token(obj);
>         err = err ? : bpf_object__probe_loading(obj);

[...]





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