[PATCH bpf-next v2] selftests/bpf: Ignore .llvm.<hash> suffix in kallsyms_find()

[PATCH bpf-next v2] selftests/bpf: Ignore .llvm.<hash> suffix in kallsyms_find()

[Yonghong Song]

I hit the following failure when running selftests with
internal backported upstream kernel:
  test_ksyms:PASS:kallsyms_fopen 0 nsec
  test_ksyms:FAIL:ksym_find symbol 'bpf_link_fops' not found
  #123     ksyms:FAIL

In /proc/kallsyms, we have
  $ cat /proc/kallsyms | grep bpf_link_fops
  ffffffff829f0cb0 d bpf_link_fops.llvm.12608678492448798416
The CONFIG_LTO_CLANG_THIN is enabled in the kernel which is responsible
for bpf_link_fops.llvm.12608678492448798416 symbol name.

In prog_tests/ksyms.c we have
  kallsyms_find("bpf_link_fops", &link_fops_addr)
and kallsyms_find() compares "bpf_link_fops" with symbols
in /proc/kallsyms in order to find the entry. With
bpf_link_fops.llvm.<hash> in /proc/kallsyms, the kallsyms_find()
failed.

To fix the issue, in kallsyms_find(), if a symbol has suffix
.llvm.<hash>, that suffix will be ignored for comparison.
This fixed the test failure.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 tools/testing/selftests/bpf/trace_helpers.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 70e29f316fe7..dc871e642ed5 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -221,6 +221,18 @@ int kallsyms_find(const char *sym, unsigned long long *addr)
 		return -EINVAL;
 
 	while (fscanf(f, "%llx %c %499s%*[^\n]\n", &value, &type, name) > 0) {
+		/* If CONFIG_LTO_CLANG_THIN is enabled, static variable/function
+		 * symbols could be promoted to global due to cross-file inlining.
+		 * For such cases, clang compiler will add .llvm.<hash> suffix
+		 * to those symbols to avoid potential naming conflict.
+		 * Let us ignore .llvm.<hash> suffix during symbol comparison.
+		 */
+		if (type == 'd') {
+			char *res = strstr(name, ".llvm.");
+
+			if (res)
+				*res = '\0';
+		}
 		if (strcmp(name, sym) == 0) {
 			*addr = value;
 			goto out;
-- 
2.43.0

Re: [PATCH bpf-next v2] selftests/bpf: Ignore .llvm.<hash> suffix in kallsyms_find()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Tue,  4 Jun 2024 11:00:34 -0700 you wrote:
> I hit the following failure when running selftests with
> internal backported upstream kernel:
>   test_ksyms:PASS:kallsyms_fopen 0 nsec
>   test_ksyms:FAIL:ksym_find symbol 'bpf_link_fops' not found
>   #123     ksyms:FAIL
> 
> In /proc/kallsyms, we have
>   $ cat /proc/kallsyms | grep bpf_link_fops
>   ffffffff829f0cb0 d bpf_link_fops.llvm.12608678492448798416
> The CONFIG_LTO_CLANG_THIN is enabled in the kernel which is responsible
> for bpf_link_fops.llvm.12608678492448798416 symbol name.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2] selftests/bpf: Ignore .llvm.<hash> suffix in kallsyms_find()
    https://git.kernel.org/bpf/bpf-next/c/898ac74c5b5f

You are awesome, thank you!
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