On Fri, Aug 30, 2024 at 12:30 AM Tony Ambardar <tony.ambardar@xxxxxxxxx> wrote:
>
> Allow static linking object files of either endianness, checking that input
> files have consistent byte-order, and setting output endianness from input.
>
> Linking requires in-memory processing of programs, relocations, sections,
> etc. in native endianness, and output conversion to target byte-order. This
> is enabled by built-in ELF translation and recent BTF/BTF.ext endianness
> functions. Further add local functions for swapping byte-order of sections
> containing BPF insns.
>
> Signed-off-by: Tony Ambardar <tony.ambardar@xxxxxxxxx>
> ---
> tools/lib/bpf/linker.c | 90 ++++++++++++++++++++++++++++++++++--------
> 1 file changed, 74 insertions(+), 16 deletions(-)
>
[...]
>
> +static bool is_exec_sec(struct dst_sec *sec)
> +{
> + if (!sec || sec->ephemeral)
> + return false;
> + return (sec->shdr->sh_type == SHT_PROGBITS) &&
> + (sec->shdr->sh_flags & SHF_EXECINSTR);
> +}
> +
> +static int exec_sec_bswap(void *raw_data, int size)
> +{
> + const int insn_cnt = size / sizeof(struct bpf_insn);
> + struct bpf_insn *insn = raw_data;
> + int i;
> +
> + if (size % sizeof(struct bpf_insn))
> + return -EINVAL;
this shouldn't be checked here, it should be assumed this is valid and
was ensured by the caller. And make exec_sec_bswap() a void function,
please.
> + for (i = 0; i < insn_cnt; i++, insn++)
> + bpf_insn_bswap(insn);
> + return 0;
> +}
> +
> static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct src_sec *src)
> {
> void *tmp;
> @@ -1170,6 +1203,10 @@ static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct src
> memset(dst->raw_data + dst->sec_sz, 0, dst_align_sz - dst->sec_sz);
> /* now copy src data at a properly aligned offset */
> memcpy(dst->raw_data + dst_align_sz, src->data->d_buf, src->shdr->sh_size);
> +
the check for size % sizeof(struct bpf_insn) should be somewhere here
(if is_exec_sec()), right?
> + /* convert added bpf insns to native byte-order */
> + if (linker->swapped_endian && is_exec_sec(dst))
> + exec_sec_bswap(dst->raw_data + dst_align_sz, src->shdr->sh_size);
> }
>
> dst->sec_sz = dst_final_sz;
> @@ -2630,6 +2667,10 @@ int bpf_linker__finalize(struct bpf_linker *linker)
> if (!sec->scn)
> continue;
>
but no need to check here, we know it's correct, if we got all the way here
> + /* restore sections with bpf insns to target byte-order */
> + if (linker->swapped_endian && is_exec_sec(sec))
> + exec_sec_bswap(sec->raw_data, sec->sec_sz);
> +
> sec->data->d_buf = sec->raw_data;
> }
>
> @@ -2698,6 +2739,7 @@ static int emit_elf_data_sec(struct bpf_linker *linker, const char *sec_name,
>
> static int finalize_btf(struct bpf_linker *linker)
> {
> + enum btf_endianness link_endianness;
> LIBBPF_OPTS(btf_dedup_opts, opts);
> struct btf *btf = linker->btf;
> const void *raw_data;
> @@ -2742,6 +2784,22 @@ static int finalize_btf(struct bpf_linker *linker)
> return err;
> }
>
> + /* Set .BTF and .BTF.ext output byte order */
> + link_endianness = linker->elf_hdr->e_ident[EI_DATA] == ELFDATA2MSB ?
> + BTF_BIG_ENDIAN : BTF_LITTLE_ENDIAN;
> + err = btf__set_endianness(linker->btf, link_endianness);
> + if (err) {
> + pr_warn("failed to set .BTF output endianness: %d\n", err);
> + return err;
> + }
link_endianness is always well-formed enum, there is no need to check
errors, here and for btf_ext__set_endianness, please drop both
> + if (linker->btf_ext) {
> + err = btf_ext__set_endianness(linker->btf_ext, link_endianness);
> + if (err) {
> + pr_warn("failed to set .BTF.ext output endianness: %d\n", err);
> + return err;
> + }
> + }
> +
> /* Emit .BTF section */
> raw_data = btf__raw_data(linker->btf, &raw_sz);
> if (!raw_data)
> --
> 2.34.1
>
