On Fri, Jun 30, 2023 at 1:35 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Adding elf_resolve_syms_offsets function that looks up
> offsets for symbols specified in syms array argument.
>
> Offsets are returned in allocated array with the 'cnt' size,
> that needs to be released by the caller.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> tools/lib/bpf/elf.c | 105 +++++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf_elf.h | 2 +
> 2 files changed, 107 insertions(+)
>
> diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
> index fcce4bd2478f..7e2f3b2e1fb6 100644
> --- a/tools/lib/bpf/elf.c
> +++ b/tools/lib/bpf/elf.c
> @@ -271,3 +271,108 @@ long elf_find_func_offset_from_file(const char *binary_path, const char *name)
> elf_close(&elf_fd);
> return ret;
> }
> +
> +struct symbol {
> + const char *name;
> + int bind;
> + int idx;
> +};
> +
> +static int symbol_cmp(const void *_a, const void *_b)
> +{
> + const struct symbol *a = _a;
> + const struct symbol *b = _b;
please, let's not (over)use leading underscores, x/y, s1/s2, whatever
> +
> + return strcmp(a->name, b->name);
> +}
> +
probably worth leaving a comment that the caller should free offsets on success?
> +int elf_resolve_syms_offsets(const char *binary_path, int cnt,
> + const char **syms, unsigned long **poffsets)
> +{
> + int sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
> + int err = 0, i, cnt_done = 0;
> + unsigned long *offsets;
> + struct symbol *symbols;
> + struct elf_fd elf_fd;
> +
> + err = elf_open(binary_path, &elf_fd);
> + if (err)
> + return err;
> +
> + offsets = calloc(cnt, sizeof(*offsets));
> + symbols = calloc(cnt, sizeof(*symbols));
> +
> + if (!offsets || !symbols) {
> + err = -ENOMEM;
> + goto out;
> + }
> +
> + for (i = 0; i < cnt; i++) {
> + symbols[i].name = syms[i];
> + symbols[i].idx = i;
> + }
> +
> + qsort(symbols, cnt, sizeof(*symbols), symbol_cmp);
> +
> + for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
> + struct elf_sym_iter iter;
> + struct elf_sym *sym;
> +
> + err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
> + if (err) {
> + if (err == -ENOENT)
> + continue;
> + goto out;
> + }
same nit, no need for nested ifs
> +
> + while ((sym = elf_sym_iter_next(&iter))) {
> + int bind = GELF_ST_BIND(sym->sym.st_info);
> + struct symbol *found, tmp = {
> + .name = sym->name,
> + };
> + unsigned long *offset;
> +
> + found = bsearch(&tmp, symbols, cnt, sizeof(*symbols), symbol_cmp);
> + if (!found)
> + continue;
> +
> + offset = &offsets[found->idx];
> + if (*offset > 0) {
> + /* same offset, no problem */
> + if (*offset == elf_sym_offset(sym))
> + continue;
> + /* handle multiple matches */
> + if (found->bind != STB_WEAK && bind != STB_WEAK) {
> + /* Only accept one non-weak bind. */
> + pr_warn("elf: ambiguous match foundr '%s', '%s' in '%s'\n",
typo: found
but also wouldn't sym->name and found->name be always the same? Maybe
log sym->name, previous *offset and newly calculated
elf_sym_offset(sym) instead?
> + sym->name, found->name, binary_path);
> + err = -LIBBPF_ERRNO__FORMAT;
I'd minimize using those custom libbpf-only errors, why not -ESRCH here?
> + goto out;
> + } else if (bind == STB_WEAK) {
> + /* already have a non-weak bind, and
> + * this is a weak bind, so ignore.
> + */
> + continue;
> + }
> + } else {
> + cnt_done++;
> + }
> + *offset = elf_sym_offset(sym);
maybe remember elf_sym_offset() result in a variable? you are using it
in two (and with my suggestion above it will be three) places already
> + found->bind = bind;
> + }
> + }
> +
> + if (cnt != cnt_done) {
> + err = -ENOENT;
> + goto out;
> + }
> +
> + *poffsets = offsets;
> +
> +out:
> + free(symbols);
> + if (err)
> + free(offsets);
> + elf_close(&elf_fd);
> + return err;
> +}
> diff --git a/tools/lib/bpf/libbpf_elf.h b/tools/lib/bpf/libbpf_elf.h
> index c763ac35a85e..026c7b378727 100644
> --- a/tools/lib/bpf/libbpf_elf.h
> +++ b/tools/lib/bpf/libbpf_elf.h
> @@ -16,4 +16,6 @@ void elf_close(struct elf_fd *elf_fd);
> long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name);
> long elf_find_func_offset_from_file(const char *binary_path, const char *name);
>
> +int elf_resolve_syms_offsets(const char *binary_path, int cnt,
> + const char **syms, unsigned long **poffsets);
> #endif /* *__LIBBPF_LIBBPF_ELF_H */
> --
> 2.41.0
>
