From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit 4fb877aaa179dcdb1676d55216482febaada457e ]
Fix bug in btf_dump's logic of determining if a given struct type is packed or not. The notion of "natural alignment" is not needed and is even harmful in this case, so drop it altogether. The biggest difference in btf_is_struct_packed() compared to its original implementation is that we don't really use btf__align_of() to determine overall alignment of a struct type (because it could be 1 for both packed and non-packed struct, depending on specifci field definitions), and just use field's actual alignment to calculate whether any field is requiring packing or struct's size overall necessitates packing.
Add two simple test cases that demonstrate the difference this change would make.
Fixes: ea2ce1ba99aa ("libbpf: Fix BTF-to-C converter's padding logic") Reported-by: Eduard Zingerman eddyz87@gmail.com Signed-off-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Eduard Zingerman eddyz87@gmail.com Link: https://lore.kernel.org/bpf/20221215183605.4149488-1-andrii@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/btf_dump.c | 33 ++++--------------- .../bpf/progs/btf_dump_test_case_packing.c | 19 +++++++++++ 2 files changed, 25 insertions(+), 27 deletions(-)
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index 77fcc5883a954..8b1ba4b725e31 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -817,47 +817,26 @@ static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id) } }
-static int btf_natural_align_of(const struct btf *btf, __u32 id) -{ - const struct btf_type *t = btf__type_by_id(btf, id); - int i, align, vlen; - const struct btf_member *m; - - if (!btf_is_composite(t)) - return btf__align_of(btf, id); - - align = 1; - m = btf_members(t); - vlen = btf_vlen(t); - for (i = 0; i < vlen; i++, m++) { - align = max(align, btf__align_of(btf, m->type)); - } - - return align; -} - static bool btf_is_struct_packed(const struct btf *btf, __u32 id, const struct btf_type *t) { const struct btf_member *m; - int align, i, bit_sz; + int max_align = 1, align, i, bit_sz; __u16 vlen;
- align = btf_natural_align_of(btf, id); - /* size of a non-packed struct has to be a multiple of its alignment */ - if (align && (t->size % align) != 0) - return true; - m = btf_members(t); vlen = btf_vlen(t); /* all non-bitfield fields have to be naturally aligned */ for (i = 0; i < vlen; i++, m++) { - align = btf_natural_align_of(btf, m->type); + align = btf__align_of(btf, m->type); bit_sz = btf_member_bitfield_size(t, i); if (align && bit_sz == 0 && m->offset % (8 * align) != 0) return true; + max_align = max(align, max_align); } - + /* size of a non-packed struct has to be a multiple of its alignment */ + if (t->size % max_align != 0) + return true; /* * if original struct was marked as packed, but its layout is * naturally aligned, we'll detect that it's not packed diff --git a/tools/testing/selftests/bpf/progs/btf_dump_test_case_packing.c b/tools/testing/selftests/bpf/progs/btf_dump_test_case_packing.c index 3f7755247591c..22dbd12134347 100644 --- a/tools/testing/selftests/bpf/progs/btf_dump_test_case_packing.c +++ b/tools/testing/selftests/bpf/progs/btf_dump_test_case_packing.c @@ -116,6 +116,23 @@ struct usb_host_endpoint { long: 0; };
+/* ----- START-EXPECTED-OUTPUT ----- */ +struct nested_packed_struct { + int a; + char b; +} __attribute__((packed)); + +struct outer_nonpacked_struct { + short a; + struct nested_packed_struct b; +}; + +struct outer_packed_struct { + short a; + struct nested_packed_struct b; +} __attribute__((packed)); + +/* ------ END-EXPECTED-OUTPUT ------ */
int f(struct { struct packed_trailing_space _1; @@ -128,6 +145,8 @@ int f(struct { union jump_code_union _8; struct outer_implicitly_packed_struct _9; struct usb_host_endpoint _10; + struct outer_nonpacked_struct _11; + struct outer_packed_struct _12; } *_) { return 0;