[PATCHv3 bpf-next 10/26] libbpf: Add elf_resolve_syms_offsets function

[Jiri Olsa <jolsa@kernel.org>]

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@kernel.org>
---
 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;
+
+	return strcmp(a->name, b->name);
+}
+
+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;
+		}
+
+		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",
+						sym->name, found->name, binary_path);
+					err = -LIBBPF_ERRNO__FORMAT;
+					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);
+			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