Merge branch 'bpf-reject-attaching-fexit-fmod_ret-to-noreturn-functions'

Yafang Shao says:

====================
Attaching fexit probes to functions marked with __noreturn may lead to
unpredictable behavior. To avoid this, we will reject attaching probes to
such functions. Currently, there is no ideal solution, so we will hardcode
a check for all __noreturn functions.

Once a more robust solution is implemented, this workaround can be removed.

v4->v5:
- Remove unnecessary functions (Alexei)
- Use BTF_ID directly (Alexei)

v3->v4: https://lore.kernel.org/bpf/20250317121735.86515-1-laoar.shao@gmail.com/
- Reject also fmod_ret (Alexei)
- Fix build warnings and remove unnecessary functions (Alexei)

v1->v2: https://lore.kernel.org/bpf/20250223062735.3341-1-laoar.shao@gmail.com/
- keep tools/objtool/noreturns.h as is (Josh)
- Add noreturns.h to objtool/sync-check.sh (Josh)
- Add verbose for the reject and simplify the test case (Song)

v1: https://lore.kernel.org/bpf/20250211023359.1570-1-laoar.shao@gmail.com/
====================

Link: https://patch.msgid.link/20250318114447.75484-1-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 24 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_noreturns.c b/tools/testing/selftests/bpf/prog_tests/fexit_noreturns.c
new file mode 100644
index 000000000000..568d3aa48a78
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_noreturns.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "fexit_noreturns.skel.h"
+
+void test_fexit_noreturns(void)
+{
+	RUN_TESTS(fexit_noreturns);
+}
diff --git a/tools/testing/selftests/bpf/progs/fexit_noreturns.c b/tools/testing/selftests/bpf/progs/fexit_noreturns.c
new file mode 100644
index 000000000000..54654539f550
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/fexit_noreturns.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("fexit/do_exit")
+__failure __msg("Attaching fexit/fmod_ret to __noreturn functions is rejected.")
+int BPF_PROG(noreturns)
+{
+	return 0;
+}