On Fri, Aug 30, 2024 at 02:25:07PM -0700, Andrii Nakryiko wrote:
On Fri, Aug 30, 2024 at 12:30 AM Tony Ambardar tony.ambardar@gmail.com 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@gmail.com
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
I did a pass earlier to reorganize sanity checks and remove redundant ones, and realized linker_sanity_check_elf() already does what we want but overlooked dropping this from exec_sec_bswap(). Will do so now. Thanks for catching!
/* 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
Right, makes sense.
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