[PATCH 6.1 160/798] selftests/bpf: Fix compile if backtrace support missing in libc

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tony Ambardar <tony.ambardar@xxxxxxxxx>

[ Upstream commit c9a83e76b5a96801a2c7ea0a79ca77c356d8b38d ]

Include GNU <execinfo.h> header only with glibc and provide weak, stubbed
backtrace functions as a fallback in test_progs.c. This allows for non-GNU
replacements while avoiding compile errors (e.g. with musl libc) like:

  test_progs.c:13:10: fatal error: execinfo.h: No such file or directory
     13 | #include <execinfo.h> /* backtrace */
        |          ^~~~~~~~~~~~
  test_progs.c: In function 'crash_handler':
  test_progs.c:1034:14: error: implicit declaration of function 'backtrace' [-Werror=implicit-function-declaration]
   1034 |         sz = backtrace(bt, ARRAY_SIZE(bt));
        |              ^~~~~~~~~
  test_progs.c:1045:9: error: implicit declaration of function 'backtrace_symbols_fd' [-Werror=implicit-function-declaration]
   1045 |         backtrace_symbols_fd(bt, sz, STDERR_FILENO);
        |         ^~~~~~~~~~~~~~~~~~~~

Fixes: 9fb156bb82a3 ("selftests/bpf: Print backtrace on SIGSEGV in test_progs")
Signed-off-by: Tony Ambardar <tony.ambardar@xxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/aa6dc8e23710cb457b278039d0081de7e7b4847d.1722244708.git.tony.ambardar@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/testing/selftests/bpf/test_progs.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
index e78289b72739f..11d4c51c7d211 100644
--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/tools/testing/selftests/bpf/test_progs.c
@@ -10,13 +10,27 @@
 #include <sched.h>
 #include <signal.h>
 #include <string.h>
-#include <execinfo.h> /* backtrace */
 #include <sys/sysinfo.h> /* get_nprocs */
 #include <netinet/in.h>
 #include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/un.h>
 
+#ifdef __GLIBC__
+#include <execinfo.h> /* backtrace */
+#endif
+
+/* Default backtrace funcs if missing at link */
+__weak int backtrace(void **buffer, int size)
+{
+	return 0;
+}
+
+__weak void backtrace_symbols_fd(void *const *buffer, int size, int fd)
+{
+	dprintf(fd, "<backtrace not supported>\n");
+}
+
 static bool verbose(void)
 {
 	return env.verbosity > VERBOSE_NONE;
-- 
2.43.0