On Wed, 2021-10-20 at 16:10 -0700, Andrii Nakryiko wrote:
> On Wed, Oct 20, 2021 at 4:05 PM Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> wrote:
> >
> > On Wed, 2021-10-20 at 11:44 -0700, Andrii Nakryiko wrote:
> > > 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).
> >
> > I thought about this, but it won't cover the ptr_sz case. Maybe we
> > just need two functions - I'll give it a try tomorrow.
> >
>
> Sorry, what's the ptr_sz case? Is this about btf_ptr_sz() helper
> somehow?
Almost, I'm referring to this check:
static int btf_dump_ptr_data(struct btf_dump *d,
const struct btf_type *t,
__u32 id,
const void *data)
{
if (ptr_is_aligned(data, d->ptr_sz) && d->ptr_sz ==
sizeof(void *)) {
...
