selftests/bpf: Add unit tests with bpf_unreachable() kfunc

The compiler support for bpf_unreachable() ([1]) will be in llvm21,
but the current kernel will have a build failure with llvm21 ([2]).
So all unit tests have explicit references to bpf_unreachable().
The test where bpf_unreachable() is generated by compiler will be
provided later.

  [1] llvm/llvm-project#131731
  [2] https://patchew.org/linux/[email protected]/

Signed-off-by: Yonghong Song <[email protected]>

Author: Yonghong Song

tools/testing/selftests/bpf/prog_tests/verifier.c

@@ -14,6 +14,7 @@
 #include "verifier_bounds_deduction_non_const.skel.h"
 #include "verifier_bounds_mix_sign_unsign.skel.h"
 #include "verifier_bpf_get_stack.skel.h"
+#include "verifier_bpf_unreachable.skel.h"
 #include "verifier_bswap.skel.h"
 #include "verifier_btf_ctx_access.skel.h"
 #include "verifier_btf_unreliable_prog.skel.h"
@@ -148,6 +149,7 @@ void test_verifier_bounds_deduction(void)     { RUN(verifier_bounds_deduction);
 void test_verifier_bounds_deduction_non_const(void)     { RUN(verifier_bounds_deduction_non_const); }
 void test_verifier_bounds_mix_sign_unsign(void) { RUN(verifier_bounds_mix_sign_unsign); }
 void test_verifier_bpf_get_stack(void)        { RUN(verifier_bpf_get_stack); }
+void test_verifier_bpf_unreachable(void)      { RUN(verifier_bpf_unreachable); }
 void test_verifier_bswap(void)                { RUN(verifier_bswap); }
 void test_verifier_btf_ctx_access(void)       { RUN(verifier_btf_ctx_access); }
 void test_verifier_btf_unreliable_prog(void)  { RUN(verifier_btf_unreliable_prog); }

tools/testing/selftests/bpf/progs/verifier_bpf_unreachable.c

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+SEC("socket")
+__description("bpf_unreachable with simple c code")
+__failure __msg("unexpected bpf_unreachable() due to uninitialized variable?")
+void bpf_unreachable_with_simple_c(void)
+{
+	bpf_unreachable();
+}
+
+SEC("socket")
+__description("bpf_unreachable as the second-from-last insn")
+__failure __msg("unexpected bpf_unreachable() due to uninitialized variable?")
+__naked void bpf_unreachable_at_func_end(void)
+{
+	asm volatile (
+	"r0 = 0;"
+	"call %[bpf_unreachable];"
+	"exit;"
+	:
+	: __imm(bpf_unreachable)
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("dead code bpf_unreachable() in the middle of code")
+__success
+__naked void dead_bpf_unreachable_in_middle(void)
+{
+	asm volatile (
+	"r0 = 0;"
+	"if r0 == 0 goto +1;"
+	"call %[bpf_unreachable];"
+	"r0 = 2;"
+	"exit;"
+	:
+	: __imm(bpf_unreachable)
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("reachable bpf_unreachable() in the middle of code")
+__failure __msg("unexpected bpf_unreachable() due to uninitialized variable?")
+__naked void live_bpf_unreachable_in_middle(void)
+{
+	asm volatile (
+	"r0 = 0;"
+	"if r0 == 1 goto +1;"
+	"call %[bpf_unreachable];"
+	"r0 = 2;"
+	"exit;"
+	:
+	: __imm(bpf_unreachable)
+	: __clobber_all);
+}
+
+char _license[] SEC("license") = "GPL";