[PATCH bpf-next v2 18/20] selftests/bpf: Add an end-to-end .bpf_cleanup exception test

[Yonghong Song <yonghong.song@linux.dev>]

C has no unwinding, so nothing here comes out of the frontend: the frames
that own a resource are written as __naked inline assembly, which spells
out by hand exactly what a frontend emits -- a call site bracketed by two
labels, a landing pad unreachable in the compiler's CFG, and a .bpf_cleanup
record tying them together. The assembler turns ".long <text label>" into
the same R_BPF_64_NODYLD32 relocation the BPF AsmPrinter emits, so libbpf
and the kernel see an object indistinguishable from a compiler-generated
one.

Call chain: entry -> foo1 -> foo1v -> foo2 -> foo3. foo3 holds a
non-preemptible section and throws inside it; foo2 holds an RCU read lock
and has two call sites sharing one pad, one of them its own throw; foo1v is
a void frame whose pad ends in a jump to a resume block placed after an
unrelated block that ends in a plain exit; foo1 owns nothing and gets no
record; entry is the boundary.

There are also some shapes the kernel refuses -- the ones with no correct
answer, and the ones a pad running on the bpf_throw() walker's stack cannot
express -- plus the return-value rejection that delivering an exception at
the boundary of a program type which constrains its return value produces.
The test skips rather than fails where the JIT cannot dispatch a landing
pad at all.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 .../selftests/bpf/exceptions_cleanup.h        |  29 +
 .../bpf/prog_tests/exceptions_cleanup.c       |  79 +++
 .../selftests/bpf/progs/exceptions_cleanup.c  | 152 +++++
 .../bpf/progs/exceptions_cleanup_fail.c       | 600 ++++++++++++++++++
 4 files changed, 860 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/exceptions_cleanup.h
 create mode 100644 tools/testing/selftests/bpf/prog_tests/exceptions_cleanup.c
 create mode 100644 tools/testing/selftests/bpf/progs/exceptions_cleanup.c
 create mode 100644 tools/testing/selftests/bpf/progs/exceptions_cleanup_fail.c

diff --git a/tools/testing/selftests/bpf/exceptions_cleanup.h b/tools/testing/selftests/bpf/exceptions_cleanup.h
new file mode 100644
index 000000000000..630d2e207119
--- /dev/null
+++ b/tools/testing/selftests/bpf/exceptions_cleanup.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#ifndef __EXCEPTIONS_CLEANUP_H__
+#define __EXCEPTIONS_CLEANUP_H__
+
+#define THROW_COOKIE		0x100
+
+/* progs/exceptions_cleanup.c: one bit per frame that reports it ran. */
+#define RAN_FOO3_PREEMPT	0x1
+#define RAN_FOO2_RCU		0x2
+#define RAN_FOO1V_PREEMPT	0x4
+#define RAN_FOO2_DROP		0x8
+#define RAN_BUMP		0x10
+
+#define CLEANUP_REC(begin, end, landing_pad)			\
+	".pushsection .bpf_cleanup,\"a\",@progbits;"		\
+	".long " begin ";"					\
+	".long " end ";"					\
+	".long " landing_pad ";"				\
+	".popsection;"
+
+/* Set a bit in @pads_ran. */
+#define PAD_RAN(bit)						\
+	"r1 = %[pads_ran] ll;"					\
+	"r2 = *(u64 *)(r1 + 0);"				\
+	"r2 |= " bit ";"					\
+	"*(u64 *)(r1 + 0) = r2;"
+
+#endif /* __EXCEPTIONS_CLEANUP_H__ */
diff --git a/tools/testing/selftests/bpf/prog_tests/exceptions_cleanup.c b/tools/testing/selftests/bpf/prog_tests/exceptions_cleanup.c
new file mode 100644
index 000000000000..d1e45b765af2
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/exceptions_cleanup.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include "exceptions_cleanup.h"
+#include "exceptions_cleanup.skel.h"
+#include "exceptions_cleanup_fail.skel.h"
+
+/* foo3 threw: every frame that has a pad ran it. */
+#define PADS_FOO3_THREW \
+	(RAN_FOO3_PREEMPT | RAN_FOO2_RCU | RAN_FOO1V_PREEMPT | RAN_FOO2_DROP)
+
+/* foo2 threw after foo3 returned normally: foo3's pad must not run. */
+#define PADS_FOO2_THREW \
+	(RAN_FOO2_RCU | RAN_FOO1V_PREEMPT | RAN_FOO2_DROP)
+
+static void run(struct exceptions_cleanup *skel, __u64 input, __u32 retval,
+		__u64 pads)
+{
+	__u64 ctx = 0;
+	int err;
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		    .ctx_in = &ctx,
+		    .ctx_size_in = sizeof(ctx),
+	);
+
+	skel->bss->input = input;
+	skel->bss->pads_ran = 0;
+	skel->bss->result = 0;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.entry), &topts);
+	if (!ASSERT_OK(err, "run"))
+		return;
+	ASSERT_EQ(topts.retval, retval, "retval");
+	ASSERT_EQ(skel->bss->pads_ran, pads | RAN_BUMP, "pads_ran");
+}
+
+void test_exceptions_cleanup(void)
+{
+	char log[8192] = {};
+	LIBBPF_OPTS(bpf_object_open_opts, opts,
+		    .kernel_log_buf = log,
+		    .kernel_log_size = sizeof(log));
+	struct exceptions_cleanup *skel;
+	int err;
+
+	skel = exceptions_cleanup__open_opts(&opts);
+	if (!ASSERT_OK_PTR(skel, "open"))
+		return;
+
+	err = exceptions_cleanup__load(skel);
+	if (err) {
+		if (err == -EOPNOTSUPP &&
+		    strstr(log, "exception cleanup needs a JIT that can dispatch landing pads"))
+			test__skip();
+		else if (!ASSERT_OK(err, "load"))
+			fprintf(stderr, "%s", log);
+		exceptions_cleanup__destroy(skel);
+		return;
+	}
+
+	/* No throw: foo3 returns 1 ^ 1 == 0, foo2 adds one, no pad runs. */
+	if (test__start_subtest("no_throw"))
+		run(skel, 1, 1, 0);
+
+	/* foo3 throws; every pad runs and the cookie is delivered at entry. */
+	if (test__start_subtest("throw_from_foo3"))
+		run(skel, 101, THROW_COOKIE, PADS_FOO3_THREW);
+
+	/* foo3 returns 2 ^ 1 == 3, so foo2 throws from its own second region;
+	 * foo3's frame is long gone, so its pad must not run.
+	 */
+	if (test__start_subtest("throw_from_foo2"))
+		run(skel, 2, THROW_COOKIE, PADS_FOO2_THREW);
+
+	exceptions_cleanup__destroy(skel);
+
+	RUN_TESTS(exceptions_cleanup_fail);
+}
diff --git a/tools/testing/selftests/bpf/progs/exceptions_cleanup.c b/tools/testing/selftests/bpf/progs/exceptions_cleanup.c
new file mode 100644
index 000000000000..95199a2828fa
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/exceptions_cleanup.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "exceptions_cleanup.h"
+
+static __used __noinline void __kfunc_btf_anchor(void)
+{
+	bpf_throw(0);
+	bpf_rcu_read_lock();
+	bpf_rcu_read_unlock();
+	bpf_preempt_disable();
+	bpf_preempt_enable();
+	bpf_unwind_resume();
+}
+
+__u64 input = 0;
+__u64 pads_ran = 0;
+__u64 result = 0;
+
+static __used __noinline __u64 foo3(__u64 x)
+{
+	bpf_preempt_disable();
+	if (x > 100)
+		asm volatile (
+		"r1 = %[cookie];"
+	"1:"	"call bpf_throw;"		/* cleanup region */
+	"2:"
+		"goto 3f;"
+	"4:"					/* landing pad */
+		"r7 = r0;"
+		"call bpf_preempt_enable;"
+		PAD_RAN("%[ran]")
+		"r1 = r7;"
+		"call bpf_unwind_resume;"
+	"3:"
+		CLEANUP_REC("1b", "2b", "4b")
+		:
+		: [cookie]"i"(THROW_COOKIE), [ran]"i"(RAN_FOO3_PREEMPT),
+		  __imm_addr(pads_ran)
+		: __clobber_all);
+	bpf_preempt_enable();
+	return x ^ 1;
+}
+
+__u64 never = 0;
+
+static __used __naked __noinline void drop_glue(void)
+{
+	asm volatile (
+	PAD_RAN("%[ran]")
+	"exit;"
+	:
+	: [ran]"i"(RAN_FOO2_DROP), __imm_addr(pads_ran)
+	: __clobber_all);
+}
+
+static __used __naked __noinline __u64 foo2(void)
+{
+	asm volatile (
+	"r6 = r1;"
+	"call bpf_rcu_read_lock;"
+	"r1 = r6;"
+"1:"	"call foo3;"			/* cleanup region #1 */
+"2:"
+	"r6 = r0;"
+	"if r6 == 0 goto 5f;"
+	"r1 = %[cookie];"
+"3:"	"call bpf_throw;"		/* cleanup region #2 */
+"4:"
+	"r0 = 0;"
+	"exit;"
+"5:"
+	"call bpf_rcu_read_unlock;"
+	"r0 = r6;"
+	"r0 += 1;"
+	"exit;"
+"6:"					/* landing pad, shared by both regions */
+	"call drop_glue;"
+	"call bpf_rcu_read_unlock;"
+	PAD_RAN("%[ran_rcu]")
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "6b")
+	CLEANUP_REC("3b", "4b", "6b")
+	:
+	: [cookie]"i"(THROW_COOKIE), [ran_rcu]"i"(RAN_FOO2_RCU),
+	  __imm_addr(pads_ran)
+	: __clobber_all);
+}
+
+static __used __naked __noinline void foo1v(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+	"r1 = %[input] ll;"
+	"r1 = *(u64 *)(r1 + 0);"
+"1:"	"call foo2;"			/* cleanup region */
+"2:"
+	"r6 = r0;"
+	"call bpf_preempt_enable;"
+	"r1 = %[result] ll;"
+	"*(u64 *)(r1 + 0) = r6;"
+	"goto 7f;"
+"8:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	PAD_RAN("%[ran]")
+	"goto 9f;"
+"7:"					/* the frame's own exit block */
+	"r0 = 0;"
+	"exit;"
+"9:"					/* shared resume block */
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "8b")
+	:
+	: [ran]"i"(RAN_FOO1V_PREEMPT), __imm_addr(input),
+	  __imm_addr(result), __imm_addr(pads_ran)
+	: __clobber_all);
+}
+
+static __used __naked __noinline void bump(void)
+{
+	asm volatile (
+	PAD_RAN("%[ran]")
+	"r1 = %[never] ll;"
+	"r1 = *(u64 *)(r1 + 0);"
+	"if r1 == 0 goto 1f;"
+	"r1 = 0;"
+	"call bpf_throw;"
+"1:"
+	"exit;"				/* r0 deliberately left alone */
+	:
+	: [ran]"i"(RAN_BUMP), __imm_addr(never), __imm_addr(pads_ran)
+	: __clobber_all);
+}
+
+__noinline __u64 foo1(void)
+{
+	bump();
+	foo1v();
+	return result;
+}
+
+SEC("syscall")
+int entry(void *ctx)
+{
+	return foo1();
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/exceptions_cleanup_fail.c b/tools/testing/selftests/bpf/progs/exceptions_cleanup_fail.c
new file mode 100644
index 000000000000..ce2dac306a84
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/exceptions_cleanup_fail.c
@@ -0,0 +1,600 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_experimental.h"
+#include "bpf_misc.h"
+#include "../test_kmods/bpf_testmod_kfunc.h"
+#include "exceptions_cleanup.h"
+
+__u64 input = 0;
+
+static __used __noinline void __kfunc_btf_anchor(void)
+{
+	bpf_throw(0);
+	bpf_preempt_disable();
+	bpf_preempt_enable();
+	bpf_unwind_resume();
+}
+
+/*
+ * 1. A subprogram that may unwind, also used as a helper callback:
+ * bpf_loop()'s own kernel frame would end the walk before it found a
+ * boundary.
+ */
+static int throwing_cb(__u32 idx, void *ctx)
+{
+	bpf_throw(0xbad);
+	return 0;
+}
+
+static __used __naked __noinline __u64 cb_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+"1:"	"call throwing_cb;"		/* cleanup region */
+"2:"
+	"call bpf_preempt_enable;"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("may unwind and is used as a callback")
+int callback_may_unwind(void *ctx)
+{
+	bpf_loop(1, throwing_cb, NULL, 0);
+	return cb_frame();
+}
+
+/*
+ * 2. A landing pad that reaches both an unwind resume and a plain exit, so
+ * nothing says whether it is a cleanup pad or a catch pad.
+ */
+static __used __naked __noinline __u64 inner_throw(void)
+{
+	asm volatile (
+	"r1 = 1;"
+	"call bpf_throw;"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+static __used __naked __noinline __u64 ambiguous_pad_frame(void)
+{
+	asm volatile (
+	"r6 = r1;"
+	"call bpf_preempt_disable;"
+"1:"	"call inner_throw;"		/* cleanup region */
+"2:"
+	"call bpf_preempt_enable;"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad: two ways out */
+	"call bpf_preempt_enable;"
+	"if r6 > 10 goto 4f;"
+	"call bpf_unwind_resume;"
+	"exit;"
+"4:"
+	"r0 = 0;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("reaches both bpf_unwind_resume() and a plain exit")
+int ambiguous_landing_pad(void *ctx)
+{
+	return ambiguous_pad_frame();
+}
+
+/*
+ * 3. A throw from inside a landing pad: a second walk over the frames the
+ * first one is in the middle of discarding.
+ */
+static __used __naked __noinline __u64 throw_in_pad_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+"1:"	"call inner_throw;"		/* cleanup region */
+"2:"
+	"call bpf_preempt_enable;"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad that throws again */
+	"call bpf_preempt_enable;"
+	"r1 = 2;"
+	"call bpf_throw;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("can throw while an exception is in flight")
+int throw_from_landing_pad(void *ctx)
+{
+	return throw_in_pad_frame();
+}
+
+/*
+ * 4. A cleanup table in a program that also installs an exception callback,
+ * two different answers to what runs on the way out.
+ */
+__noinline int unused_exc_cb(u64 cookie)
+{
+	return 0;
+}
+
+static __used __naked __noinline __u64 cb_and_table_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+	"r1 = 9;"
+"1:"	"call bpf_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__exception_cb(unused_exc_cb)
+__failure __msg("cannot be combined with an exception callback")
+int table_with_exception_cb(void *ctx)
+{
+	return cb_and_table_frame();
+}
+
+__u64 never;
+
+/*
+ * 5. A landing pad that calls a subprogram which can throw. Not case 3: the
+ * throw is in another subprogram, so what catches it is the walk of the pad's
+ * body, off subprog_info.might_throw.
+ */
+static __used __noinline void pad_callee_that_throws(void)
+{
+	if (never)
+		bpf_throw(0);
+}
+
+static __used __naked __noinline __u64 pad_calls_thrower_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+	"r1 = 11;"
+"1:"	"call bpf_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call pad_callee_that_throws;"	/* ...which can throw: refused */
+	"call bpf_preempt_enable;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("which can throw while an exception is in flight")
+int pad_calls_thrower(void *ctx)
+{
+	return pad_calls_thrower_frame();
+}
+
+/*
+ * 6. A catch pad: it ends in a plain exit rather than a resume, and a walker
+ * that calls pads as subroutines cannot hand a frame back its own execution.
+ */
+static __used __naked __noinline __u64 catch_pad_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+	"r1 = 12;"
+"1:"	"call bpf_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* catch pad: no resume, it stops here */
+	"call bpf_preempt_enable;"
+	"r0 = 0;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("is not supported yet, only cleanup pads that resume")
+int catch_landing_pad(void *ctx)
+{
+	return catch_pad_frame();
+}
+
+/*
+ * 7. An exception reaching the boundary of a program type that constrains
+ * its return value: delivery makes the cookie that return value, and fentry
+ * has to return 0.
+ */
+static __used __naked __noinline __u64 boundary_throw_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+	"r1 = 7;"
+"1:"	"call bpf_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?fentry/bpf_fentry_test1")
+__failure __msg("the register R1 has smin=7 smax=7 should have been in [0, 0]")
+int boundary_delivers(void *ctx)
+{
+	return boundary_throw_frame();
+}
+
+/*
+ * 8. A bpf_unwind_resume() outside any landing pad. Both JITs lower it as
+ * the way back out of a pad, which in ordinary code leaves a live frame
+ * standing with its epilogue skipped.
+ */
+static __used __naked __noinline __u64 stray_resume_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+	"r1 = 13;"
+"1:"	"call bpf_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("is not in an exception cleanup landing pad")
+int resume_outside_pad(void *ctx)
+{
+	/* Never taken, but reachable, which is all the verifier needs. */
+	if (never)
+		bpf_unwind_resume();
+	return stray_resume_frame();
+}
+
+/*
+ * 9. A bpf_unwind_resume() in a subprogram a landing pad calls. The
+ * verifier's walk cannot tell it from a resume in the pad itself -- an
+ * exception is in flight either way -- so the rule is static: a resume sits in
+ * a pad body.
+ */
+static __used __naked __noinline void resume_in_callee(void)
+{
+	asm volatile (
+	"call bpf_unwind_resume;"
+	"exit;"
+	::: __clobber_all);
+}
+
+static __used __naked __noinline __u64 pad_calls_resumer_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+	"r1 = 14;"
+"1:"	"call bpf_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	"call resume_in_callee;"	/* ...which resumes: refused */
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("is not in an exception cleanup landing pad")
+int resume_in_pad_callee(void *ctx)
+{
+	return pad_calls_resumer_frame();
+}
+
+/*
+ * 10. A bpf_unwind_resume() in a program carrying no cleanup table, where
+ * that static rule does not run at all. do_check() refuses it on the state not
+ * unwinding, and has to: the JITs lower every one of these the same way.
+ */
+static __used __naked __noinline __u64 no_table_resume_frame(void)
+{
+	asm volatile (
+	"call bpf_unwind_resume;"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("reached without an exception in flight")
+int resume_without_table(void *ctx)
+{
+	return no_table_resume_frame();
+}
+
+/*
+ * 11. A landing pad that is itself a covered call site, so an exception out
+ * of it would have nowhere to go. Hand-written only: LLVM sinks a function's
+ * pads past every range it emits.
+ */
+static __used __naked __noinline __u64 nested_pad_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+"1:"	"call inner_throw;"		/* first cleanup region */
+"2:"
+	"call bpf_preempt_enable;"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* first pad, second region's call */
+	"call bpf_preempt_enable;"
+"4:"
+	"call bpf_unwind_resume;"
+	"exit;"
+"5:"					/* second pad */
+	"call bpf_preempt_enable;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	CLEANUP_REC("3b", "4b", "5b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("is inside the call-site range of")
+int nested_landing_pad(void *ctx)
+{
+	return nested_pad_frame();
+}
+
+/*
+ * 12. A tail call in a landing pad: it unwinds the prologue off the stack
+ * pointer, which in a pad is the walker's.
+ */
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+} tc_map SEC(".maps");
+
+static __used __naked __noinline __u64 tail_call_pad_frame(void)
+{
+	asm volatile (
+	"r6 = r1;"
+"1:"	"call inner_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"r1 = r6;"
+	"r2 = %[tc_map] ll;"
+	"r3 = 0;"
+	"call %[bpf_tail_call];"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	:
+	: __imm(bpf_tail_call), __imm_addr(tc_map)
+	: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("is in an exception cleanup landing pad")
+int tail_call_in_pad(void *ctx)
+{
+	return tail_call_pad_frame();
+}
+
+#if defined(__BPF_FEATURE_STACK_ARGUMENT)
+
+/*
+ * 13. A call that passes an argument on the stack, in a landing pad: the
+ * outgoing area the callee reads is not the one the caller wrote, the frame
+ * being the unwinding one and the stack pointer the walker's.
+ */
+static __used __noinline __u64 six_args(__u64 a, __u64 b, __u64 c, __u64 d,
+					__u64 e, __u64 f)
+{
+	return a + b + c + d + e + f;
+}
+
+static __used __naked __noinline __u64 stack_arg_pad_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+"1:"	"call inner_throw;"		/* cleanup region */
+"2:"
+	"call bpf_preempt_enable;"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	"r1 = 1;"
+	"r2 = 2;"
+	"r3 = 3;"
+	"r4 = 4;"
+	"r5 = 5;"
+	"*(u64 *)(r11 - 8) = 6;"	/* the sixth argument */
+	"call six_args;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("on-stack call argument in an exception cleanup landing pad")
+int stack_arg_in_pad(void *ctx)
+{
+	return stack_arg_pad_frame();
+}
+
+/*
+ * 14. The same, reached the other way: a kfunc whose by-value argument runs
+ * past the five argument registers, where the JIT fills the outgoing area and
+ * the rule above has no store to catch. The C call gives the extern its BTF.
+ */
+static __used __noinline void __nofit_btf_anchor(void)
+{
+	struct prog_test_pair_arg s = {};
+
+	bpf_kfunc_call_test_pair_arg_nofit(1, 2, 3, 4, s);
+}
+
+static __used __naked __noinline __u64 kfunc_arg_pad_frame(void)
+{
+	asm volatile (
+	"call bpf_preempt_disable;"
+"1:"	"call inner_throw;"		/* cleanup region */
+"2:"
+	"call bpf_preempt_enable;"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"call bpf_preempt_enable;"
+	"r1 = 1;"
+	"r2 = 2;"
+	"r3 = 3;"
+	"r4 = 4;"
+	"r5 = 5;"
+	"call bpf_kfunc_call_test_pair_arg_nofit;"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("on-stack call argument in an exception cleanup landing pad")
+int kfunc_stack_arg_in_pad(void *ctx)
+{
+	return kfunc_arg_pad_frame();
+}
+
+#endif /* __BPF_FEATURE_STACK_ARGUMENT */
+
+/*
+ * 15. A landing pad entered by ordinary control flow, arriving with none of
+ * what the walker sets up. Nothing static sees it -- the resume really is in a
+ * pad body -- so do_check() refuses it on the state not unwinding.
+ */
+static __used __naked __noinline __u64 jump_into_pad_frame(void)
+{
+	asm volatile (
+	"r1 = %[input] ll;"
+	"r6 = *(u64 *)(r1 + 0);"
+	"if r6 > 7 goto 4f;"		/* an ordinary branch into the pad */
+"1:"	"call inner_throw;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"r7 = r0;"
+"4:"					/* ... and its second instruction */
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	:
+	: __imm_addr(input)
+	: __clobber_all);
+}
+
+SEC("?syscall")
+__failure __msg("reached without an exception in flight")
+int jump_into_pad(void *ctx)
+{
+	return jump_into_pad_frame();
+}
+
+#if defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)
+
+/*
+ * 16. A landing pad that reaches an indirect jump, which cannot be told from
+ * a catch pad. SEC("socket") because a jump table entry is an offset from the
+ * program's section symbol, and "?syscall" is not a name assembly can use.
+ */
+static __used __naked __noinline void gotox_thrower(void)
+{
+	asm volatile (
+	"r1 = 15;"
+	"call bpf_throw;"
+	"exit;"
+	::: __clobber_all);
+}
+
+SEC("socket")
+__failure __msg("reaches an indirect jump")
+__naked void gotox_in_pad(void)
+{
+	asm volatile (
+	".pushsection .jumptables,\"\",@progbits;"
+"jt0_%=:"
+	".quad l0_%= - socket;"
+	".quad l1_%= - socket;"
+	".size jt0_%=, 16;"
+	".global jt0_%=;"
+	".popsection;"
+
+"1:"	"call gotox_thrower;"		/* cleanup region */
+"2:"
+	"r0 = 0;"
+	"exit;"
+"3:"					/* landing pad */
+	"r1 = jt0_%= ll;"
+	"r1 += 8;"
+	"r2 = *(u64 *)(r1 + 0);"
+	/* gotox r2. Spelled as a raw insn on purpose: the "gotox" mnemonic
+	 * only reached the LLVM assembler in llvm 22, and BPF_RAW_INSN()
+	 * needs <linux/bpf.h>, which this file cannot have -- vmlinux.h
+	 * already defines the uapi enums.
+	 */
+	".8byte 0x20d;"
+"l0_%=:"
+	"call bpf_unwind_resume;"
+	"exit;"
+"l1_%=:"
+	"call bpf_unwind_resume;"
+	"exit;"
+	CLEANUP_REC("1b", "2b", "3b")
+	::: __clobber_all);
+}
+
+#endif /* x86 || arm64 */
+
+char _license[] SEC("license") = "GPL";
-- 
2.53.0-Meta