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.ambar...@gmail.com>
---
tools/lib/bpf/linker.c | 78 +++++++++++++++++++++++++++++++++---------
1 file changed, 62 insertions(+), 16 deletions(-)
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 6985ab0f1ca9..81dbbdd79a7c 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("unknown byte order of ELF file %s\n", filename);
+ return err;
+ }
+ if (link_byteorder == ELFDATANONE) {
+ linker->elf_hdr->e_ident[EI_DATA] = 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_elf("unsupported byte order of ELF file %s", filename);
+ pr_warn("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 +1123,24 @@ 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 void 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;
+
+ for (i = 0; i < insn_cnt; i++, insn++)
+ bpf_insn_bswap(insn);
+}
+
static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct
src_sec *src)
{
void *tmp;
@@ -1170,6 +1200,10 @@ 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);
+
+ /* 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 +2664,10 @@ 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))
+ exec_sec_bswap(sec->raw_data, sec->sec_sz);
+
sec->data->d_buf = sec->raw_data;
}
@@ -2698,6 +2736,7 @@ 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 +2781,13 @@ 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;
+ btf__set_endianness(linker->btf, link_endianness);
+ if (linker->btf_ext)
+ btf_ext__set_endianness(linker->btf_ext, link_endianness);
+
/* Emit .BTF section */
raw_data = btf__raw_data(linker->btf, &raw_sz);
if (!raw_data)
--
2.34.1
