Re: [PATCH bpf-next v5 5/8] libbpf: Support opening bpf objects of either endianness

On Tue, Sep 3, 2024 at 12:33 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 | 52 +++++++++++++++++++++++++++------ tools/lib/bpf/libbpf_internal.h | 11 +++++++ 2 files changed, 54 insertions(+), 9 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 0226d3b50709..46f41ea5e74d 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -694,6 +694,8 @@ struct bpf_object { /* Information when doing ELF related work. Only valid if efile.elf is not NULL */ struct elf_state efile;

•   unsigned char byteorder;
  

•   struct btf *btf;
    struct btf_ext *btf_ext;
  
  

@@ -940,6 +942,21 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data, return 0; }

+static void bpf_object_bswap_progs(struct bpf_object *obj) +{

•   struct bpf_program *prog = obj->programs;
  

•   struct bpf_insn *insn;
  

•   int p, i;
  

•   for (p = 0; p < obj->nr_programs; p++, prog++) {
  

•           insn = prog->insns;
  

•           for (i = 0; i < prog->insns_cnt; i++, insn++)
  

•                   bpf_insn_bswap(insn);
  

•   }
  

•   pr_debug("converted %zu BPF programs to native byte order\n",
  

•            obj->nr_programs);
  

Does it fit in 100 characters? If yes, it stays on single line. That's the rule for all code, don't wrap lines unnecessarily.

+}

static const struct btf_member * find_member_by_offset(const struct btf_type *t, __u32 bit_offset) { @@ -1506,6 +1523,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)

    elf_end(obj->efile.elf);
    obj->efile.elf = NULL;

•   obj->efile.ehdr = NULL;
    obj->efile.symbols = NULL;
    obj->efile.arena_data = NULL;
  
  

@@ -1571,6 +1589,16 @@ static int bpf_object__elf_init(struct bpf_object *obj) goto errout; }

•   /* 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 save after bpf_object_open() frees ELF data */
  

•   obj->byteorder = ehdr->e_ident[EI_DATA];
  

•   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));
  

@@ -1599,19 +1627,15 @@ static int bpf_object__elf_init(struct bpf_object *obj) return err; }

-static int bpf_object__check_endianness(struct bpf_object *obj) +static bool is_native_endianness(struct bpf_object *obj) { #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__

•   if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2LSB)
  

•           return 0;
  

•   return obj->byteorder == ELFDATA2LSB;
  

#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__

•   if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
  

•           return 0;
  

•   return obj->byteorder == ELFDATA2MSB;
  

#else # error "Unrecognized __BYTE_ORDER__" #endif

•   pr_warn("elf: endianness mismatch in %s.\n", obj->path);
  

•   return -LIBBPF_ERRNO__ENDIAN;
  

}

static int @@ -3953,6 +3977,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj) return -LIBBPF_ERRNO__FORMAT; }

•   /* change BPF program insns to native endianness for introspection */
  

•   if (!is_native_endianness(obj))
  

•           bpf_object_bswap_progs(obj);
  

•   /* sort BPF programs by section name and in-section instruction offset
     * for faster search
     */
  

@@ -7992,7 +8020,6 @@ static struct bpf_object *bpf_object_open(const char *path, const void *obj_buf, }

    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);
  

@@ -8498,8 +8525,15 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch return libbpf_err(-EINVAL); }

•   if (obj->gen_loader)
  

•   /* Disallow kernel loading programs of non-native endianness but
  

•    * permit cross-endian creation of "light skeleton".
  

•    */
  

•   if (obj->gen_loader) {
            bpf_gen__init(obj->gen_loader, extra_log_level, obj->nr_programs, obj->nr_maps);
  

•   } else if (!is_native_endianness(obj)) {
  

•           pr_warn("object '%s': loading non-native endianness is unsupported\n", obj->name);
  

•           return libbpf_err(-LIBBPF_ERRNO__ENDIAN);
  

•   }
  
    err = bpf_object_prepare_token(obj);
    err = err ? : bpf_object__probe_loading(obj);
  

diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h index a8531195acd4..eda7a0cc2b8c 100644 --- a/tools/lib/bpf/libbpf_internal.h +++ b/tools/lib/bpf/libbpf_internal.h @@ -11,6 +11,7 @@

#include <stdlib.h> #include <limits.h> +#include <byteswap.h> #include <errno.h> #include <linux/err.h> #include <fcntl.h> @@ -616,6 +617,16 @@ static inline bool is_ldimm64_insn(struct bpf_insn *insn) return insn->code == (BPF_LD | BPF_IMM | BPF_DW); }

+static inline void bpf_insn_bswap(struct bpf_insn *insn) +{

•   __u8 tmp_reg = insn->dst_reg;
  

•   insn->dst_reg = insn->src_reg;
  

•   insn->src_reg = tmp_reg;
  

•   insn->off = bswap_16(insn->off);
  

•   insn->imm = bswap_32(insn->imm);
  

+}

/* Unconditionally dup FD, ensuring it doesn't use [0, 2] range.

• Original FD is not closed or altered in any other way.
• Preserves original FD value, if it's invalid (negative).

-- 2.34.1