selftests/bpf: Ignore .llvm.<hash> suffix in kallsyms_find()

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
  torvalds#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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240604180034.1356016-1-yonghong.song@linux.dev

tools/testing/selftests/bpf/trace_helpers.c

@@ -211,7 +211,7 @@ long ksym_get_addr(const char *name)
  */
 int kallsyms_find(const char *sym, unsigned long long *addr)
 {
-	char type, name[500];
+	char type, name[500], *match;
 	unsigned long long value;
 	int err = 0;
 	FILE *f;
@@ -221,6 +221,17 @@ 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') {
+			match = strstr(name, ".llvm.");
+			if (match)
+				*match = '\0';
+		}
 		if (strcmp(name, sym) == 0) {
 			*addr = value;
 			goto out;