Commit 7257cee6 authored Sep 18, 2023 by Hengqi Chen Committed by Andrii Nakryiko Sep 22, 2023

libbpf: Resolve symbol conflicts at the same offset for uprobe



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.

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20230918024813.237475-2-hengqi.chen@gmail.com

parent ac0691c7

tools/lib/bpf/elf.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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);