[PATCHv5 bpf-next 08/28] libbpf: Move elf_find_func_offset* functions to elf object

Jiri Olsa
2023-07-30T13:43:49Z

Adding new elf object that will contain elf related functions.
There's no functional change.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/lib/bpf/Build | 2 +-
tools/lib/bpf/elf.c | 197 ++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.c | 185 ------------------------------
tools/lib/bpf/libbpf_internal.h | 4 +
4 files changed, 202 insertions(+), 186 deletions(-)
create mode 100644 tools/lib/bpf/elf.c

diff --git a/tools/lib/bpf/Build b/tools/lib/bpf/Build
index b8b0a6369363..2d0c282c8588 100644
--- a/tools/lib/bpf/Build
+++ b/tools/lib/bpf/Build
@@ -1,4 +1,4 @@
libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o str_error.o \
netlink.o bpf_prog_linfo.o libbpf_probes.o hashmap.o \
btf_dump.o ringbuf.o strset.o linker.o gen_loader.o relo_core.o \
- usdt.o zip.o
+ usdt.o zip.o elf.o
diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
new file mode 100644
index 000000000000..735ef10093ac
--- /dev/null
+++ b/tools/lib/bpf/elf.c
@@ -0,0 +1,197 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+#include <libelf.h>
+#include <gelf.h>
+#include <fcntl.h>
+#include <linux/kernel.h>
+
+#include "libbpf_internal.h"
+#include "str_error.h"
+
+#define STRERR_BUFSIZE 128
+
+/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
+static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
+{
+ while ((scn = elf_nextscn(elf, scn)) != NULL) {
+ GElf_Shdr sh;
+
+ if (!gelf_getshdr(scn, &sh))
+ continue;
+ if (sh.sh_type == sh_type)
+ return scn;
+ }
+ return NULL;
+}
+
+/* Find offset of function name in the provided ELF object. "binary_path" is
+ * the path to the ELF binary represented by "elf", and only used for error
+ * reporting matters. "name" matches symbol name or name@@LIB for library
+ * functions.
+ */
+long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
+{
+ int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
+ bool is_shared_lib, is_name_qualified;
+ long ret = -ENOENT;
+ size_t name_len;
+ GElf_Ehdr ehdr;
+
+ if (!gelf_getehdr(elf, &ehdr)) {
+ pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
+ ret = -LIBBPF_ERRNO__FORMAT;
+ goto out;
+ }
+ /* for shared lib case, we do not need to calculate relative offset */
+ is_shared_lib = ehdr.e_type == ET_DYN;
+
+ name_len = strlen(name);
+ /* Does name specify "@@LIB"? */
+ is_name_qualified = strstr(name, "@@") != NULL;
+
+ /* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
+ * a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
+ * linked binary may not have SHT_DYMSYM, so absence of a section should not be
+ * reported as a warning/error.
+ */
+ for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
+ size_t nr_syms, strtabidx, idx;
+ Elf_Data *symbols = NULL;
+ Elf_Scn *scn = NULL;
+ int last_bind = -1;
+ const char *sname;
+ GElf_Shdr sh;
+
+ scn = elf_find_next_scn_by_type(elf, sh_types[i], NULL);
+ if (!scn) {
+ pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
+ binary_path);
+ continue;
+ }
+ if (!gelf_getshdr(scn, &sh))
+ continue;
+ strtabidx = sh.sh_link;
+ symbols = elf_getdata(scn, 0);
+ if (!symbols) {
+ pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
+ binary_path, elf_errmsg(-1));
+ ret = -LIBBPF_ERRNO__FORMAT;
+ goto out;
+ }
+ nr_syms = symbols->d_size / sh.sh_entsize;
+
+ for (idx = 0; idx < nr_syms; idx++) {
+ int curr_bind;
+ GElf_Sym sym;
+ Elf_Scn *sym_scn;
+ GElf_Shdr sym_sh;
+
+ if (!gelf_getsym(symbols, idx, &sym))
+ continue;
+
+ if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
+ continue;
+
+ sname = elf_strptr(elf, strtabidx, sym.st_name);
+ if (!sname)
+ continue;
+
+ curr_bind = GELF_ST_BIND(sym.st_info);
+
+ /* User can specify func, func@@LIB or func@@LIB_VERSION. */
+ if (strncmp(sname, name, name_len) != 0)
+ continue;
+ /* ...but we don't want a search for "foo" to match 'foo2" also, so any
+ * additional characters in sname should be of the form "@@LIB".
+ */
+ if (!is_name_qualified && sname[name_len] != '\0' && sname[name_len] != '@')
+ continue;
+
+ if (ret >= 0) {
+ /* handle multiple matches */
+ if (last_bind != STB_WEAK && curr_bind != STB_WEAK) {
+ /* Only accept one non-weak bind. */
+ pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
+ sname, name, binary_path);
+ ret = -LIBBPF_ERRNO__FORMAT;
+ goto out;
+ } else if (curr_bind == STB_WEAK) {
+ /* already have a non-weak bind, and
+ * this is a weak bind, so ignore.
+ */
+ continue;
+ }
+ }
+
+ /* Transform symbol's virtual address (absolute for
+ * binaries and relative for shared libs) into file
+ * offset, which is what kernel is expecting for
+ * uprobe/uretprobe attachment.
+ * See Documentation/trace/uprobetracer.rst for more
+ * details.
+ * This is done by looking up symbol's containing
+ * section's header and using it's virtual address
+ * (sh_addr) and corresponding file offset (sh_offset)
+ * to transform sym.st_value (virtual address) into
+ * desired final file offset.
+ */
+ sym_scn = elf_getscn(elf, sym.st_shndx);
+ if (!sym_scn)
+ continue;
+ if (!gelf_getshdr(sym_scn, &sym_sh))
+ continue;
+
+ ret = sym.st_value - sym_sh.sh_addr + sym_sh.sh_offset;
+ last_bind = curr_bind;
+ }
+ if (ret > 0)
+ break;
+ }
+
+ if (ret > 0) {
+ pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
+ ret);
+ } else {
+ if (ret == 0) {
+ pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
+ is_shared_lib ? "should not be 0 in a shared library" :
+ "try using shared library path instead");
+ ret = -ENOENT;
+ } else {
+ pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
+ }
+ }
+out:
+ return ret;
+}
+
+/* Find offset of function name in ELF object specified by path. "name" matches
+ * symbol name or name@@LIB for library functions.
+ */
+long elf_find_func_offset_from_file(const char *binary_path, const char *name)
+{
+ char errmsg[STRERR_BUFSIZE];
+ long ret = -ENOENT;
+ Elf *elf;
+ int fd;
+
+ fd = open(binary_path, O_RDONLY | O_CLOEXEC);
+ if (fd < 0) {
+ ret = -errno;
+ pr_warn("failed to open %s: %s\n", binary_path,
+ libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
+ return ret;
+ }
+ elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+ if (!elf) {
+ pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
+ close(fd);
+ return -LIBBPF_ERRNO__FORMAT;
+ }
+
+ ret = elf_find_func_offset(elf, binary_path, name);
+ elf_end(elf);
+ close(fd);
+ return ret;
+}
+
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2fc98d857142..1bdda3f8c865 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10986,191 +10986,6 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe,
return err;
}

-/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
-static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
-{
- while ((scn = elf_nextscn(elf, scn)) != NULL) {
- GElf_Shdr sh;
-
- if (!gelf_getshdr(scn, &sh))
- continue;
- if (sh.sh_type == sh_type)
- return scn;
- }
- return NULL;
-}
-
-/* Find offset of function name in the provided ELF object. "binary_path" is
- * the path to the ELF binary represented by "elf", and only used for error
- * reporting matters. "name" matches symbol name or name@@LIB for library
- * functions.
- */
-static long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
-{
- int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
- bool is_shared_lib, is_name_qualified;
- long ret = -ENOENT;
- size_t name_len;
- GElf_Ehdr ehdr;
-
- if (!gelf_getehdr(elf, &ehdr)) {
- pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
- ret = -LIBBPF_ERRNO__FORMAT;
- goto out;
- }
- /* for shared lib case, we do not need to calculate relative offset */
- is_shared_lib = ehdr.e_type == ET_DYN;
-
- name_len = strlen(name);
- /* Does name specify "@@LIB"? */
- is_name_qualified = strstr(name, "@@") != NULL;
-
- /* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
- * a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
- * linked binary may not have SHT_DYMSYM, so absence of a section should not be
- * reported as a warning/error.
- */
- for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
- size_t nr_syms, strtabidx, idx;
- Elf_Data *symbols = NULL;
- Elf_Scn *scn = NULL;
- int last_bind = -1;
- const char *sname;
- GElf_Shdr sh;
-
- scn = elf_find_next_scn_by_type(elf, sh_types[i], NULL);
- if (!scn) {
- pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
- binary_path);
- continue;
- }
- if (!gelf_getshdr(scn, &sh))
- continue;
- strtabidx = sh.sh_link;
- symbols = elf_getdata(scn, 0);
- if (!symbols) {
- pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
- binary_path, elf_errmsg(-1));
- ret = -LIBBPF_ERRNO__FORMAT;
- goto out;
- }
- nr_syms = symbols->d_size / sh.sh_entsize;
-
- for (idx = 0; idx < nr_syms; idx++) {
- int curr_bind;
- GElf_Sym sym;
- Elf_Scn *sym_scn;
- GElf_Shdr sym_sh;
-
- if (!gelf_getsym(symbols, idx, &sym))
- continue;
-
- if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
- continue;
-
- sname = elf_strptr(elf, strtabidx, sym.st_name);
- if (!sname)
- continue;
-
- curr_bind = GELF_ST_BIND(sym.st_info);
-
- /* User can specify func, func@@LIB or func@@LIB_VERSION. */
- if (strncmp(sname, name, name_len) != 0)
- continue;
- /* ...but we don't want a search for "foo" to match 'foo2" also, so any
- * additional characters in sname should be of the form "@@LIB".
- */
- if (!is_name_qualified && sname[name_len] != '\0' && sname[name_len] != '@')
- continue;
-
- if (ret >= 0) {
- /* handle multiple matches */
- if (last_bind != STB_WEAK && curr_bind != STB_WEAK) {
- /* Only accept one non-weak bind. */
- pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
- sname, name, binary_path);
- ret = -LIBBPF_ERRNO__FORMAT;
- goto out;
- } else if (curr_bind == STB_WEAK) {
- /* already have a non-weak bind, and
- * this is a weak bind, so ignore.
- */
- continue;
- }
- }
-
- /* Transform symbol's virtual address (absolute for
- * binaries and relative for shared libs) into file
- * offset, which is what kernel is expecting for
- * uprobe/uretprobe attachment.
- * See Documentation/trace/uprobetracer.rst for more
- * details.
- * This is done by looking up symbol's containing
- * section's header and using it's virtual address
- * (sh_addr) and corresponding file offset (sh_offset)
- * to transform sym.st_value (virtual address) into
- * desired final file offset.
- */
- sym_scn = elf_getscn(elf, sym.st_shndx);
- if (!sym_scn)
- continue;
- if (!gelf_getshdr(sym_scn, &sym_sh))
- continue;
-
- ret = sym.st_value - sym_sh.sh_addr + sym_sh.sh_offset;
- last_bind = curr_bind;
- }
- if (ret > 0)
- break;
- }
-
- if (ret > 0) {
- pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
- ret);
- } else {
- if (ret == 0) {
- pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
- is_shared_lib ? "should not be 0 in a shared library" :
- "try using shared library path instead");
- ret = -ENOENT;
- } else {
- pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
- }
- }
-out:
- return ret;
-}
-
-/* Find offset of function name in ELF object specified by path. "name" matches
- * symbol name or name@@LIB for library functions.
- */
-static long elf_find_func_offset_from_file(const char *binary_path, const char *name)
-{
- char errmsg[STRERR_BUFSIZE];
- long ret = -ENOENT;
- Elf *elf;
- int fd;
-
- fd = open(binary_path, O_RDONLY | O_CLOEXEC);
- if (fd < 0) {
- ret = -errno;
- pr_warn("failed to open %s: %s\n", binary_path,
- libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
- return ret;
- }
- elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
- if (!elf) {
- pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
- close(fd);
- return -LIBBPF_ERRNO__FORMAT;
- }
-
- ret = elf_find_func_offset(elf, binary_path, name);
- elf_end(elf);
- close(fd);
- return ret;
-}
-
/* Find offset of function name in archive specified by path. Currently
* supported are .zip files that do not compress their contents, as used on
* Android in the form of APKs, for example. "file_name" is the name of the ELF
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index e4d05662a96c..44eb63541507 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -15,6 +15,7 @@
#include <linux/err.h>
#include <fcntl.h>
#include <unistd.h>
+#include <libelf.h>
#include "relo_core.h"

/* make sure libbpf doesn't use kernel-only integer typedefs */
@@ -577,4 +578,7 @@ static inline bool is_pow_of_2(size_t x)
#define PROG_LOAD_ATTEMPTS 5
int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int attempts);

+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);
+
#endif /* __LIBBPF_LIBBPF_INTERNAL_H */
--
2.41.0