Re: [PATCH bpf-next v1 6/8] selftests/bpf: Fix compile if backtrace support missing in libc

From: Tony Ambardar <redacted>

Use backtrace functions only with glibc and otherwise provide stubs in
test_progs.c. This avoids 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 <redacted>
---
 tools/testing/selftests/bpf/test_progs.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
index 60c5ec0f6abf..f6cfc6a8e8f0 100644
--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/tools/testing/selftests/bpf/test_progs.c

@@ -10,7 +10,6 @@
 #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>

@@ -19,6 +18,14 @@
 #include <bpf/btf.h>
 #include "json_writer.h"

+#ifdef __GLIBC__
+#include <execinfo.h> /* backtrace */
+#else
+#define backtrace(...) (0)
+#define backtrace_symbols_fd(bt, sz, fd) \
+       dprintf(fd, "<backtrace not supported>\n", bt, sz)
+#endif