With llvm24 after commit 28b4a2032f97 ("[BPF] Mark global functions noipa"), the test recursion_via_global_func_and_callback fails: 13: (85) call bpf_loop#181 4: frame1: R1=scalar() R10=fp0 cb ; return static_calls_global(i); @ verifier_global_subprogs.c:548 4: (85) call pc+1 ... ; return global_calls_loop(x); @ verifier_global_subprogs.c:543 6: (85) call pc+1 Func#3 ('global_calls_loop') is global and assumed valid. 7: frame2: R0=scalar() 7: (95) exit ... ; return static_calls_global(i); @ verifier_global_subprogs.c:548 5: (95) exit At callback return the register R0 has unknown scalar value should have been in [0, 1] ============= EXPECTED SUBSTR: 'recursive call from global_calls_loop() to loop_cb_calls_static()' #669/9 verifier_global_subprogs/recursion_via_global_func_and_callback:FAIL The callback loop_cb_calls_static() returns the result of static_calls_global(), which in turn returns the result of the global function global_calls_loop(). Before the above llvm24 commit, IPSCCP (interprocedural sparse conditional constant propagation) could fold the return value of global_calls_loop() into its callers. global_calls_loop() is not static, but it has a non-weak definition in the same compilation unit, so IPSCCP may assume that definition is the one called. It found that global_calls_loop() always returns 0 and replaced the uses of the call result with 0, which made static_calls_global() and then loop_cb_calls_static() return a constant 0 as well. The calls stay, only their return values are replaced. So the callback set R0 to 0 itself, passed the bpf_loop callback return range check, and verification went on to report the expected recursion. The llvm24 commit marks global functions noipa, since the verifier checks a global function only against its BTF prototype and freplace can replace it. With noipa, IPSCCP no longer propagates the return value of global_calls_loop() to callers. The verifier does not look into a global function either, so R0 after the call is an unknown scalar, and the callback return check fails before the recursion is detected. Make static_calls_global() return void and let loop_cb_calls_static() return 0 explicitly. The call chain the test is about stays the same, and the test passes with both llvm24 and earlier versions (e.g. llvm21 to llvm23). Link: https://github.com/llvm/llvm-project/pull/237690 Signed-off-by: Yonghong Song --- .../testing/selftests/bpf/progs/verifier_global_subprogs.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c index 574b26b5a7df..5e8461b2167d 100644 --- a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c +++ b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c @@ -538,14 +538,15 @@ int return_from_void_global(struct __sk_buff *skb) int global_calls_loop(int x); -static __noinline int static_calls_global(int x) +static __noinline void static_calls_global(int x) { - return global_calls_loop(x); + global_calls_loop(x); } static __noinline int loop_cb_calls_static(u32 i, void *ctx) { - return static_calls_global(i); + static_calls_global(i); + return 0; } __noinline int global_calls_loop(int x) -- 2.53.0-Meta