From: Tony Ambardar tony.ambardar@gmail.com
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 | 106 ++++++++++++++++++++++++++++++++++------- 1 file changed, 90 insertions(+), 16 deletions(-)
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c index 7489306cd6f7..9bf218db443e 100644 --- a/tools/lib/bpf/linker.c +++ b/tools/lib/bpf/linker.c @@ -135,6 +135,7 @@ struct bpf_linker { int fd; Elf *elf; Elf64_Ehdr *elf_hdr; + bool swapped_endian;
/* Output sections metadata */ struct dst_sec *secs; @@ -324,13 +325,8 @@ static int init_output_elf(struct bpf_linker *linker, const char *file)
linker->elf_hdr->e_machine = EM_BPF; linker->elf_hdr->e_type = ET_REL; -#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ - linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2LSB; -#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ - linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2MSB; -#else -#error "Unknown __BYTE_ORDER__" -#endif + /* Set unknown ELF endianness, assign later from input files */ + linker->elf_hdr->e_ident[EI_DATA] = ELFDATANONE;
/* STRTAB */ /* initialize strset with an empty string to conform to ELF */ @@ -541,19 +537,21 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, const struct bpf_linker_file_opts *opts, struct src_obj *obj) { -#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ - const int host_endianness = ELFDATA2LSB; -#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ - const int host_endianness = ELFDATA2MSB; -#else -#error "Unknown __BYTE_ORDER__" -#endif int err = 0; Elf_Scn *scn; Elf_Data *data; Elf64_Ehdr *ehdr; Elf64_Shdr *shdr; struct src_sec *sec; + unsigned char obj_byteorder; + unsigned char *link_byteorder = &linker->elf_hdr->e_ident[EI_DATA]; +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ + const unsigned char host_byteorder = ELFDATA2LSB; +#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ + const unsigned char host_byteorder = ELFDATA2MSB; +#else +#error "Unknown __BYTE_ORDER__" +#endif
pr_debug("linker: adding object file '%s'...\n", filename);
@@ -579,11 +577,25 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, pr_warn_elf("failed to get ELF header for %s", filename); return err; } - if (ehdr->e_ident[EI_DATA] != host_endianness) { + + /* Linker output endianness set by first input object */ + obj_byteorder = ehdr->e_ident[EI_DATA]; + if (obj_byteorder != ELFDATA2LSB && obj_byteorder != ELFDATA2MSB) { err = -EOPNOTSUPP; - pr_warn_elf("unsupported byte order of ELF file %s", filename); + pr_warn("linker: unknown byte order of ELF file %s\n", filename); return err; } + if (*link_byteorder == ELFDATANONE) { + *link_byteorder = obj_byteorder; + linker->swapped_endian = obj_byteorder != host_byteorder; + pr_debug("linker: set %s-endian output byte order\n", + obj_byteorder == ELFDATA2MSB ? "big" : "little"); + } else if (*link_byteorder != obj_byteorder) { + err = -EOPNOTSUPP; + pr_warn("linker: byte order mismatch with ELF file %s\n", filename); + return err; + } + if (ehdr->e_type != ET_REL || ehdr->e_machine != EM_BPF || ehdr->e_ident[EI_CLASS] != ELFCLASS64) { @@ -1111,6 +1123,27 @@ static bool sec_content_is_same(struct dst_sec *dst_sec, struct src_sec *src_sec return true; }
+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; + 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 +1203,16 @@ 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); + + /* convert added bpf insns to native byte-order */ + if (linker->swapped_endian && is_exec_sec(dst)) { + err = exec_sec_bswap(dst->raw_data + dst_align_sz, + src->shdr->sh_size); + if (err) { + pr_warn("%s: error changing insns endianness\n", __func__); + return err; + } + } }
dst->sec_sz = dst_final_sz; @@ -2630,6 +2673,14 @@ int bpf_linker__finalize(struct bpf_linker *linker) if (!sec->scn) continue;
+ /* restore sections with bpf insns to target byte-order */ + if (linker->swapped_endian && is_exec_sec(sec)) { + err = exec_sec_bswap(sec->raw_data, sec->sec_sz); + if (err) { + pr_warn("error finalizing insns endianness\n"); + return libbpf_err(err); + } + } sec->data->d_buf = sec->raw_data; }
@@ -2696,6 +2747,13 @@ static int emit_elf_data_sec(struct bpf_linker *linker, const char *sec_name, return 0; }
+static enum btf_endianness +linker_btf_endianness(const struct bpf_linker *linker) +{ + unsigned char byteorder = linker->elf_hdr->e_ident[EI_DATA]; + return byteorder == ELFDATA2MSB ? BTF_BIG_ENDIAN : BTF_LITTLE_ENDIAN; +} + static int finalize_btf(struct bpf_linker *linker) { LIBBPF_OPTS(btf_dedup_opts, opts); @@ -2742,6 +2800,22 @@ static int finalize_btf(struct bpf_linker *linker) return err; }
+ /* Set .BTF and .BTF.ext output byte order */ + err = btf__set_endianness(linker->btf, + linker_btf_endianness(linker)); + if (err) { + pr_warn("failed to set .BTF output endianness: %d\n", err); + return err; + } + if (linker->btf_ext) { + err = btf_ext__set_endianness(linker->btf_ext, + linker_btf_endianness(linker)); + 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)