[PATCH bpf-next v4 1/3] libbpf: Resolve symbol conflicts at the same offset for uprobe

[Hengqi Chen <hengqi.chen@gmail.com>]

Dynamic symbols in shared library may have the same name, 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

Currently, users can't attach a uprobe to pthread_rwlock_wrlock because
there are two symbols named pthread_rwlock_wrlock and both are global
bind. And libbpf considers it as a conflict.

Since both of them are at the same offset we could accept one of them
harmlessly. Note that we already does this in elf_resolve_syms_offsets.

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
---
 tools/lib/bpf/elf.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
index 9d0296c1726a..5c9e588b17da 100644
--- a/tools/lib/bpf/elf.c
+++ b/tools/lib/bpf/elf.c
@@ -214,7 +214,10 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
 
 			if (ret > 0) {
 				/* handle multiple matches */
-				if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
+				if (elf_sym_offset(sym) == ret) {
+					/* same offset, no problem */
+					continue;
+				} else if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
 					/* Only accept one non-weak bind. */
 					pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
 						sym->name, name, binary_path);
-- 
2.34.1