[PATCH 5.17 178/772] selftests/bpf: fix btf_dump/btf_dump due to recent clang change

Greg Kroah-Hartman
2022-06-07T20:46:28Z

From: Yonghong Song <yhs@fb.com>

[ Upstream commit 4050764cbaa25760aab40857f723393c07898474 ]

Latest llvm-project upstream had a change of behavior
related to qualifiers on function return type ([1]).
This caused selftests btf_dump/btf_dump failure.
The following example shows what changed.

$ cat t.c
typedef const char * const (* const (* const fn_ptr_arr2_t[5])())(char * (*)(int));
struct t {
int a;
fn_ptr_arr2_t l;
};
int foo(struct t *arg) {
return arg->a;
}

Compiled with latest upstream llvm15,
$ clang -O2 -g -target bpf -S -emit-llvm t.c
The related generated debuginfo IR looks like:
!16 = !DIDerivedType(tag: DW_TAG_typedef, name: "fn_ptr_arr2_t", file: !1, line: 1, baseType: !17)
!17 = !DICompositeType(tag: DW_TAG_array_type, baseType: !18, size: 320, elements: !32)
!18 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !19)
!19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !20, size: 64)
!20 = !DISubroutineType(types: !21)
!21 = !{!22, null}
!22 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !23, size: 64)
!23 = !DISubroutineType(types: !24)
!24 = !{!25, !28}
!25 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !26, size: 64)
!26 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !27)
!27 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
You can see two intermediate const qualifier to pointer are dropped in debuginfo IR.

With llvm14, we have following debuginfo IR:
!16 = !DIDerivedType(tag: DW_TAG_typedef, name: "fn_ptr_arr2_t", file: !1, line: 1, baseType: !17)
!17 = !DICompositeType(tag: DW_TAG_array_type, baseType: !18, size: 320, elements: !34)
!18 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !19)
!19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !20, size: 64)
!20 = !DISubroutineType(types: !21)
!21 = !{!22, null}
!22 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !23)
!23 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !24, size: 64)
!24 = !DISubroutineType(types: !25)
!25 = !{!26, !30}
!26 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !27)
!27 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !28, size: 64)
!28 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !29)
!29 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
All const qualifiers are preserved.

To adapt the selftest to both old and new llvm, this patch removed
the intermediate const qualifier in const-to-ptr types, to make the
test succeed again.

[1] https://reviews.llvm.org/D125919

Reported-by: Mykola Lysenko <mykolal@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220523152044.3905809-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c b/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c
index 1c7105fcae3c..4ee4748133fe 100644
--- a/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c
+++ b/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c
@@ -94,7 +94,7 @@ typedef void (* (*signal_t)(int, void (*)(int)))(int);

typedef char * (*fn_ptr_arr1_t[10])(int **);

-typedef char * (* const (* const fn_ptr_arr2_t[5])())(char * (*)(int));
+typedef char * (* (* const fn_ptr_arr2_t[5])())(char * (*)(int));

struct struct_w_typedefs {
int_t a;
--
2.35.1