On Wed, Oct 13, 2021 at 9:09 AM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote:
>
> Currently ptr_is_aligned() takes size, and not alignment, as a
> parameter, which may be overly pessimistic e.g. for __i128 on s390,
> which must be only 8-byte aligned. Fix by using btf__align_of() where
> possible - one notable exception is ptr_sz, for which there is no
> corresponding type.
>
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---
> tools/lib/bpf/btf_dump.c | 12 +++++-------
> 1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> index 25ce60828e8d..da345520892f 100644
> --- a/tools/lib/bpf/btf_dump.c
> +++ b/tools/lib/bpf/btf_dump.c
> @@ -1657,9 +1657,9 @@ static int btf_dump_base_type_check_zero(struct btf_dump *d,
> return 0;
> }
>
> -static bool ptr_is_aligned(const void *data, int data_sz)
> +static bool ptr_is_aligned(const void *data, int alignment)
> {
> - return ((uintptr_t)data) % data_sz == 0;
> + return ((uintptr_t)data) % alignment == 0;
btf__align_of() can return 0 on error and this will be div by 0. I
think the better approach would be for ptr_is_aligned to accept struct
btf *btf and __u32 type_id, call btf__align_of() based on btf and type
id, handle 0 case pessimistically (assume not aligned).
> }
>
> static int btf_dump_int_data(struct btf_dump *d,
> @@ -1681,7 +1681,7 @@ static int btf_dump_int_data(struct btf_dump *d,
> /* handle packed int data - accesses of integers not aligned on
> * int boundaries can cause problems on some platforms.
> */
> - if (!ptr_is_aligned(data, sz)) {
> + if (!ptr_is_aligned(data, btf__align_of(d->btf, type_id))) {
> memcpy(buf, data, sz);
> data = buf;
> }
> @@ -1770,7 +1770,7 @@ static int btf_dump_float_data(struct btf_dump *d,
> int sz = t->size;
>
> /* handle unaligned data; copy to local union */
> - if (!ptr_is_aligned(data, sz)) {
> + if (!ptr_is_aligned(data, btf__align_of(d->btf, type_id))) {
> memcpy(&fl, data, sz);
> flp = &fl;
> }
> @@ -1953,10 +1953,8 @@ static int btf_dump_get_enum_value(struct btf_dump *d,
> __u32 id,
> __s64 *value)
> {
> - int sz = t->size;
> -
> /* handle unaligned enum value */
> - if (!ptr_is_aligned(data, sz)) {
> + if (!ptr_is_aligned(data, btf__align_of(d->btf, id))) {
> __u64 val;
> int err;
>
> --
> 2.31.1
>
