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From: Hengqi Chen <hengqi.chen@gmail.com>
To: bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
	hengqi.chen@gmail.com
Subject: [PATCH bpf-next 1/2] libbpf: Resolve ambiguous matches at the same offset for uprobe
Date: Mon,  4 Sep 2023 02:24:43 +0000	[thread overview]
Message-ID: <20230904022444.1695820-2-hengqi.chen@gmail.com> (raw)
In-Reply-To: <20230904022444.1695820-1-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, we can't attach a uprobe to pthread_rwlock_wrlock because
both symbols are global bind. Since both of them are at the same offset
we could accept one of them harmlessly.

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);
--
2.39.3

  reply	other threads:[~2023-09-04  2:25 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-04  2:24 [PATCH bpf-next 0/2] libbpf: Support symbol versioning for uprobe Hengqi Chen
2023-09-04  2:24 ` Hengqi Chen [this message]
2023-09-04  2:24 ` [PATCH bpf-next 2/2] " Hengqi Chen
2023-09-04 14:10   ` Jiri Olsa
2023-09-04 15:40     ` Hengqi Chen
2023-09-04  8:38 ` [PATCH bpf-next 0/2] " Alan Maguire
2023-09-04 15:30   ` Hengqi Chen

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