[PATCH bpf-next v4 3/3] selftests/bpf: Test Program Structure diagnostic context

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Exercise each corrected Program Structure report. Place a
missing-table gotox after another instruction so its attribution
differs from the subprogram start.

Add malformed subprogram layouts for a branch crossing a subprogram
boundary and a subprogram that falls through its end. Both cases carry
BTF line records and assert that their structured reports include the
corresponding source function and file.

Link: https://lore.kernel.org/bpf/cf2f420c2b21de440a7dc51b1565c0f06d4b539640ee5c03384e5d77bcfb5686@mail.kernel.org/
Link: https://lore.kernel.org/r/20260924170646.2366016-8-memxor@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../selftests/bpf/progs/verifier_cfg.c        | 40 +++++++++++++++++++
 .../selftests/bpf/progs/verifier_gotox.c      |  2 +
 2 files changed, 42 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_cfg.c b/tools/testing/selftests/bpf/progs/verifier_cfg.c
index 6379dfc9389b..b429fa7a08f5 100644
--- a/tools/testing/selftests/bpf/progs/verifier_cfg.c
+++ b/tools/testing/selftests/bpf/progs/verifier_cfg.c
@@ -56,6 +56,46 @@ __naked void out_of_range_jump2(void)
 "	::: __clobber_all);
 }
 
+static __naked __noinline __used int cross_subprog_target(void)
+{
+	asm volatile ("					\
+	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+SEC("socket")
+__description("jump across subprogram boundary")
+__failure __msg("jump out of range from insn 1")
+__msg("jump_across_subprog_boundary @ verifier_cfg.c")
+__naked void jump_across_subprog_boundary(void)
+{
+	asm volatile ("					\
+	call cross_subprog_target;			\
+	goto +1;					\
+	exit;						\
+"	::: __clobber_all);
+}
+
+static __naked __noinline __used int fallthrough_subprog(void)
+{
+	asm volatile ("					\
+	r0 = 0;						\
+"	::: __clobber_all);
+}
+
+SEC("socket")
+__description("subprogram fallthrough")
+__failure __msg("last insn is not an exit or jmp")
+__msg("fallthrough_subprog @ verifier_cfg.c")
+__naked void subprog_fallthrough(void)
+{
+	asm volatile ("					\
+	call fallthrough_subprog;			\
+	exit;						\
+"	::: __clobber_all);
+}
+
 SEC("socket")
 __description("invalid DW LDSX instruction in diagnostics")
 __failure __msg("BUG_ldx_99")
diff --git a/tools/testing/selftests/bpf/progs/verifier_gotox.c b/tools/testing/selftests/bpf/progs/verifier_gotox.c
index f5a9878c7b8d..dc7baa0f2458 100644
--- a/tools/testing/selftests/bpf/progs/verifier_gotox.c
+++ b/tools/testing/selftests/bpf/progs/verifier_gotox.c
@@ -101,9 +101,11 @@ __naked void jump_table_terminal_gotox_subprog(void)
  */
 SEC("socket")
 __failure __msg("no jump tables found for subprog starting at 0")
+__msg(">>> 1 | (0d) gotox r0")
 __naked void jump_table_no_jump_table(void)
 {
 	asm volatile ("						\
+	r0 = 0;							\
 	.8byte %[gotox_r0];					\
 	r0 = 1;							\
 	exit;							\
-- 
2.53.0