From: Alan Maguire <alan.maguire@oracle.com>
To: Hengqi Chen <hengqi.chen@gmail.com>, bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
olsajiri@gmail.com
Subject: Re: [PATCH bpf-next v2 1/3] libbpf: Resolve symbol conflicts at the same offset for uprobe
Date: Fri, 8 Sep 2023 15:30:56 +0100 [thread overview]
Message-ID: <7c7f9cb8-2dfe-b4a3-92b6-9f69dff07218@oracle.com> (raw)
In-Reply-To: <20230905151257.729192-2-hengqi.chen@gmail.com>
On 05/09/2023 16:12, Hengqi Chen wrote:
> 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>
Reviewed-by: Alan Maguire <alan.maguire@oracle.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
next prev parent reply other threads:[~2023-09-08 14:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-05 15:12 [PATCH bpf-next v2 0/3] libbpf: Support symbol versioning for uprobe Hengqi Chen
2023-09-05 15:12 ` [PATCH bpf-next v2 1/3] libbpf: Resolve symbol conflicts at the same offset " Hengqi Chen
2023-09-08 14:30 ` Alan Maguire [this message]
2023-09-10 9:53 ` Jiri Olsa
2023-09-05 15:12 ` [PATCH bpf-next v2 2/3] libbpf: Support symbol versioning " Hengqi Chen
2023-09-08 15:07 ` Alan Maguire
2023-09-10 12:39 ` Hengqi Chen
2023-09-10 9:53 ` Jiri Olsa
2023-09-10 12:42 ` Hengqi Chen
2023-09-05 15:12 ` [PATCH bpf-next v2 3/3] selftests/bpf: Add tests for " Hengqi Chen
2023-09-08 14:40 ` Alan Maguire
2023-09-10 9:53 ` Jiri Olsa
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