On Wed, Oct 21, 2020 at 12:25 PM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
>
> Em Fri, Oct 09, 2020 at 12:26:07PM -0700, Andrii Nakryiko escreveu:
> > Differentiate between struct and union forwards. For BTF_KIND_FWD this is
> > determined by kflag. So teach btf_loader to use that bit to decide whether
> > forward is for union or struct.
>
> So, before this patch 'btfdiff vmlinux' comes clean, i.e. pretty
> printing from DWARF matches pretty printing from BTF, after it:
>
> [acme@five pahole]$ btfdiff vmlinux | wc -l
> 1500
> [acme@five pahole]$
>
> One of the differences:
>
> @@ -117457,7 +117457,7 @@ struct wireless_dev {
>
> /* XXX last struct has 1 byte of padding */
>
> - struct cfg80211_cqm_config * cqm_config; /* 952 8 */
> + union cfg80211_cqm_config * cqm_config; /* 952 8 */
> /* --- cacheline 15 boundary (960 bytes) --- */
> struct list_head pmsr_list; /* 960 16 */
> spinlock_t pmsr_lock; /* 976 4 */
> [acme@five pahole]$
>
> Looking at the source code:
>
> struct wireless_dev {
> ...
> struct cfg80211_cqm_config *cqm_config;
> ...
> }
>
> Also:
>
> struct nfnl_ct_hook {
> - struct nf_conn * (*get_ct)(const struct sk_buff *, enum ip_conntrack_info *); /* 0 8 */
> - size_t (*build_size)(const struct nf_conn *); /* 8 8 */
> - int (*build)(struct sk_buff *, struct nf_conn *, enum ip_conntrack_info, u_int16_t, u_int16_t); /* 16 8 */
> - int (*parse)(const struct nlattr *, struct nf_conn *); /* 24 8 */
> - int (*attach_expect)(const struct nlattr *, struct nf_conn *, u32, u32); /* 32 8 */
> - void (*seq_adjust)(struct sk_buff *, struct nf_conn *, enum ip_conntrack_info, s32); /* 40 8 */
> + union nf_conn * (*get_ct)(const struct sk_buff *, enum ip_conntrack_info *); /* 0 8 */
> + size_t (*build_size)(const union nf_conn *); /* 8 8 */
> + int (*build)(struct sk_buff *, union nf_conn *, enum ip_conntrack_info, u_int16_t, u_int16_t); /* 16 8 */
> + int (*parse)(const struct nlattr *, union nf_conn *); /* 24 8 */
> + int (*attach_expect)(const struct nlattr *, union nf_conn *, u32, u32); /* 32 8 */
> + void (*seq_adjust)(struct sk_buff *, union nf_conn *, enum ip_conntrack_info, s32); /* 40 8 */1
>
> Looking at the source code:
>
> struct nfnl_ct_hook {
> struct nf_conn *(*get_ct)(const struct sk_buff *skb,
> enum ip_conntrack_info *ctinfo);
> size_t (*build_size)(const struct nf_conn *ct);
> int (*build)(struct sk_buff *skb, struct nf_conn *ct,
> enum ip_conntrack_info ctinfo,
> u_int16_t ct_attr, u_int16_t ct_info_attr);
> int (*parse)(const struct nlattr *attr, struct nf_conn *ct);
> int (*attach_expect)(const struct nlattr *attr, struct nf_conn *ct,
> u32 portid, u32 report);
> void (*seq_adjust)(struct sk_buff *skb, struct nf_conn *ct,
> enum ip_conntrack_info ctinfo, s32 off);
> };
>
> - Arnaldo
>
> > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > ---
> > N.B. This patch is based on top of tmp.libbtf_encoder branch.
> >
> > Also seems like non-forward declared union has a slightly different
> > representation from struct (class). Not sure why it is so, but this change
> > doesn't seem to break anything.
> > ---
> >
> > btf_loader.c | 9 +++++----
> > 1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/btf_loader.c b/btf_loader.c
> > index 9b5da3a4997a..0cb23967fec3 100644
> > --- a/btf_loader.c
> > +++ b/btf_loader.c
> > @@ -134,12 +134,13 @@ static struct type *type__new(uint16_t tag, strings_t name, size_t size)
> > return type;
> > }
> >
> > -static struct class *class__new(strings_t name, size_t size)
> > +static struct class *class__new(strings_t name, size_t size, bool is_union)
> > {
> > struct class *class = tag__alloc(sizeof(*class));
> > + uint32_t tag = is_union ? DW_TAG_union_type : DW_TAG_structure_type;
> >
> > if (class != NULL) {
> > - type__init(&class->type, DW_TAG_structure_type, name, size);
> > + type__init(&class->type, tag, name, size);
> > INIT_LIST_HEAD(&class->vtable);
> > }
> >
> > @@ -228,7 +229,7 @@ static int create_members(struct btf_elf *btfe, const struct btf_type *tp,
> >
> > static int create_new_class(struct btf_elf *btfe, const struct btf_type *tp, uint32_t id)
> > {
> > - struct class *class = class__new(tp->name_off, tp->size);
> > + struct class *class = class__new(tp->name_off, tp->size, false);
> > int member_size = create_members(btfe, tp, &class->type);
> >
> > if (member_size < 0)
> > @@ -313,7 +314,7 @@ static int create_new_subroutine_type(struct btf_elf *btfe, const struct btf_typ
> >
> > static int create_new_forward_decl(struct btf_elf *btfe, const struct btf_type *tp, uint32_t id)
> > {
> > - struct class *fwd = class__new(tp->name_off, 0);
> > + struct class *fwd = class__new(tp->name_off, 0, btf_kind(tp));
*FACEPALM*... This should be btf_kflag(tp) instead. I'll use btfdiff
on all my patches from now on, sorry about this!
> >
> > if (fwd == NULL)
> > return -ENOMEM;
> > --
> > 2.24.1
> >
>
> --
>
> - Arnaldo
