In current implementation, we assume that symbol found in .dynsym section
would have a version suffix and use it to compare with symbol user supplied.
According to the spec ([0]), this assumption is incorrect, the version info
of dynamic symbols are stored in .gnu.version and .gnu.version_d sections
of ELF objects. For example:
$ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5
$ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
706: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 __pthread_rwlock_wrlock@GLIBC_2.2.5
2568: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@@GLIBC_2.34
2571: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@GLIBC_2.2.5
In this case, specify pthread_rwlock_wrlock@@GLIBC_2.34 or
pthread_rwlock_wrlock@GLIBC_2.2.5 in bpf_uprobe_opts::func_name won't work.
Because the qualified name does NOT match `pthread_rwlock_wrlock` (without
version suffix) in .dynsym sections.
This commit implements the symbol versioning for dynsym and allows user to
specify symbol in the following forms:
- func
- func@LIB_VERSION
- func@@LIB_VERSION
In case of symbol conflicts, error out and users should resolve it by
specifying a qualified name.
[0]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>
---
tools/lib/bpf/elf.c | 134 +++++++++++++++++++++++++++++++++++++----
tools/lib/bpf/libbpf.c | 2 +-
2 files changed, 124 insertions(+), 12 deletions(-)
diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
index 5c9e588b17da..f7ad7a7acc29 100644
--- a/tools/lib/bpf/elf.c
+++ b/tools/lib/bpf/elf.c
@@ -1,5 +1,8 @@
// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
#include <libelf.h>
#include <gelf.h>
#include <fcntl.h>
@@ -10,6 +13,17 @@
#define STRERR_BUFSIZE 128
+/* A SHT_GNU_versym section holds 16-bit words. This bit is set if
+ * the symbol is hidden and can only be seen when referenced using an
+ * explicit version number. This is a GNU extension.
+ */
+#define VERSYM_HIDDEN 0x8000
+
+/* This is the mask for the rest of the data in a word read from a
+ * SHT_GNU_versym section.
+ */
+#define VERSYM_VERSION 0x7fff
+
int elf_open(const char *binary_path, struct elf_fd *elf_fd)
{
char errmsg[STRERR_BUFSIZE];
@@ -64,13 +78,18 @@ struct elf_sym {
const char *name;
GElf_Sym sym;
GElf_Shdr sh;
+ int ver;
+ bool hidden;
};
struct elf_sym_iter {
Elf *elf;
Elf_Data *syms;
+ Elf_Data *versyms;
+ Elf_Data *verdefs;
size_t nr_syms;
size_t strtabidx;
+ size_t verdef_strtabidx;
size_t next_sym_idx;
struct elf_sym sym;
int st_type;
@@ -111,6 +130,29 @@ static int elf_sym_iter_new(struct elf_sym_iter *iter,
iter->nr_syms = iter->syms->d_size / sh.sh_entsize;
iter->elf = elf;
iter->st_type = st_type;
+
+ /* Version symbol table is meaningful to dynsym only */
+ if (sh_type != SHT_DYNSYM)
+ return 0;
+
+ scn = elf_find_next_scn_by_type(elf, SHT_GNU_versym, NULL);
+ if (!scn)
+ return 0;
+ if (!gelf_getshdr(scn, &sh))
+ return -EINVAL;
+ iter->versyms = elf_getdata(scn, 0);
+
+ scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
+ if (!scn) {
+ pr_debug("elf: failed to find verdef ELF sections in '%s'\n",
+ binary_path);
+ return -ENOENT;
+ }
+ if (!gelf_getshdr(scn, &sh))
+ return -EINVAL;
+ iter->verdef_strtabidx = sh.sh_link;
+ iter->verdefs = elf_getdata(scn, 0);
+
return 0;
}
@@ -119,6 +161,7 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
struct elf_sym *ret = &iter->sym;
GElf_Sym *sym = &ret->sym;
const char *name = NULL;
+ GElf_Versym versym;
Elf_Scn *sym_scn;
size_t idx;
@@ -138,12 +181,80 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
iter->next_sym_idx = idx + 1;
ret->name = name;
+ ret->ver = 0;
+ ret->hidden = false;
+
+ if (iter->versyms) {
+ if (!gelf_getversym(iter->versyms, idx, &versym))
+ continue;
+ ret->ver = versym & VERSYM_VERSION;
+ ret->hidden = versym & VERSYM_HIDDEN;
+ }
return ret;
}
return NULL;
}
+static const char *elf_get_vername(struct elf_sym_iter *iter, int ver)
+{
+ GElf_Verdaux verdaux;
+ GElf_Verdef verdef;
+ int offset;
+
+ offset = 0;
+ while (gelf_getverdef(iter->verdefs, offset, &verdef)) {
+ if (verdef.vd_ndx != ver) {
+ if (!verdef.vd_next)
+ break;
+
+ offset += verdef.vd_next;
+ continue;
+ }
+
+ if (!gelf_getverdaux(iter->verdefs, offset + verdef.vd_aux, &verdaux))
+ break;
+
+ return elf_strptr(iter->elf, iter->verdef_strtabidx, verdaux.vda_name);
+
+ }
+ return NULL;
+}
+
+static bool symbol_match(struct elf_sym_iter *iter, int sh_type, struct elf_sym *sym,
+ const char *name, size_t name_len, const char *lib_ver)
+{
+ const char *ver_name;
+
+ /* Symbols are in forms of func, func@LIB_VER or func@@LIB_VER
+ * make sure the func part matches the user specified name
+ */
+ if (strncmp(sym->name, name, name_len) != 0)
+ return false;
+
+ /* ...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 (sym->name[name_len] != '\0' && sym->name[name_len] != '@')
+ return false;
+
+ /* If user does not specify symbol version, then we got a match */
+ if (!lib_ver)
+ return true;
+
+ /* If user specifies symbol version, for dynamic symbols,
+ * get version name from ELF verdef section for comparison.
+ */
+ if (sh_type == SHT_DYNSYM) {
+ ver_name = elf_get_vername(iter, sym->ver);
+ if (!ver_name)
+ return false;
+ return !strcmp(ver_name, lib_ver);
+ }
+
+ /* For normal symbols, it is already in form of func@LIB_VER */
+ return !strcmp(sym->name, name);
+}
/* Transform symbol's virtual address (absolute for binaries and relative
* for shared libs) into file offset, which is what kernel is expecting
@@ -166,7 +277,8 @@ static unsigned long elf_sym_offset(struct elf_sym *sym)
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;
+ const char *at_symbol, *lib_ver;
+ bool is_shared_lib;
long ret = -ENOENT;
size_t name_len;
GElf_Ehdr ehdr;
@@ -179,9 +291,15 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
/* 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;
+ /* Does name specify "@@LIB_VER" or "@LIB_VER" ? */
+ at_symbol = strchr(name, '@');
+ if (at_symbol) {
+ name_len = at_symbol - name;
+ lib_ver = strrchr(name, '@') + 1;
+ } else {
+ name_len = strlen(name);
+ lib_ver = 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
@@ -201,13 +319,7 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
goto out;
while ((sym = elf_sym_iter_next(&iter))) {
- /* User can specify func, func@@LIB or func@@LIB_VERSION. */
- if (strncmp(sym->name, 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 && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
+ if (!symbol_match(&iter, sh_types[i], sym, name, name_len, lib_ver))
continue;
cur_bind = GELF_ST_BIND(sym->sym.st_info);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3a6108e3238b..b4758e54a815 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11630,7 +11630,7 @@ static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf
*link = NULL;
- n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%li",
+ n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.@]+%li",
&probe_type, &binary_path, &func_name, &offset);
switch (n) {
case 1:
--
2.34.1
