From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit 25a4481b4136af7794e1df2d6c90ed2f354d60ce ]
btf__align_of() is supposed to be return alignment requirement of a requested BTF type. For STRUCT/UNION it doesn't always return correct value, because it calculates alignment only based on field types. But for packed structs this is not enough, we need to also check field offsets and struct size. If field offset isn't aligned according to field type's natural alignment, then struct must be packed. Similarly, if struct size is not a multiple of struct's natural alignment, then struct must be packed as well.
This patch fixes this issue precisely by additionally checking these conditions.
Fixes: 3d208f4ca111 ("libbpf: Expose btf__align_of() API") Signed-off-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20221212211505.558851-5-andrii@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/btf.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index 3ed759f53e7c2..fd23095129782 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -647,8 +647,21 @@ int btf__align_of(const struct btf *btf, __u32 id) if (align <= 0) return libbpf_err(align); max_align = max(max_align, align); + + /* if field offset isn't aligned according to field + * type's alignment, then struct must be packed + */ + if (btf_member_bitfield_size(t, i) == 0 && + (m->offset % (8 * align)) != 0) + return 1; }
+ /* if struct/union size isn't a multiple of its alignment, + * then struct must be packed + */ + if ((t->size % max_align) != 0) + return 1; + return max_align; } default: