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

On Fri, Aug 30, 2024 at 12:30 AM Tony Ambardar tony.ambardar@gmail.com 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@gmail.com

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);
  

[...]