Re: [PATCH dwarves v2 1/5] fprintf: Correct names for types with btf_type_tag attribute

Eduard Zingerman
2023-03-28T14:11:45Z

On Tue, 2023-03-28 at 10:59 -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Mar 15, 2023 at 01:04:13AM +0200, Eduard Zingerman escreveu:
> > The following example contains a structure field annotated with
> > btf_type_tag attribute:
> >
> > #define __tag1 __attribute__((btf_type_tag("tag1")))
> >
> > struct st {
> > int __tag1 *a;
> > } g;
> >
> > It is not printed correctly by `pahole -F dwarf` command:
> >
> > $ clang -g -c test.c -o test.o
> > pahole -F dwarf test.o
> > struct st {
> > tag1 * a; /* 0 8 */
> > ...
> > };
> >
> > Note the type for variable `a`: `tag1` is printed instead of `int`.
> > This commit teaches `type__fprintf()` and `__tag_name()` logic to skip
> > `DW_TAG_LLVM_annotation` objects that are used to encode type tags.
>
> I noticed this:
>
> ⬢[acme@toolbox pahole]$ pahole --sort -F btf ../vmlinux-clang-pahole-1.25+rust > /tmp/clang
> ⬢[acme@toolbox pahole]$ pahole --sort -F btf ../vmlinux-gcc-pahole-1.25+rust > /tmp/gcc
>
>
> --- /tmp/gcc 2023-03-28 10:55:37.075999474 -0300
> +++ /tmp/clang 2023-03-28 10:55:53.324436319 -0300
> @@ -70,21 +70,21 @@
> struct Qdisc {
> int (*enqueue)(struct sk_buff *, struct Qdisc *, struct sk_buff * *); /* 0 8 */
> struct sk_buff * (*dequeue)(struct Qdisc *); /* 8 8 */
> unsigned int flags; /* 16 4 */
> u32 limit; /* 20 4 */
> const struct Qdisc_ops * ops; /* 24 8 */
> - struct qdisc_size_table * stab; /* 32 8 */
> + struct qdisc_size_table stab; /* 32 8 */
> struct hlist_node hash; /* 40 16 */
> u32 handle; /* 56 4 */
> u32 parent; /* 60 4 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> struct netdev_queue * dev_queue; /* 64 8 */
> - struct net_rate_estimator * rate_est; /* 72 8 */
> - struct gnet_stats_basic_sync * cpu_bstats; /* 80 8 */
> - struct gnet_stats_queue * cpu_qstats; /* 88 8 */
> + struct net_rate_estimator rate_est; /* 72 8 */
> + struct gnet_stats_basic_sync cpu_bstats; /* 80 8 */
> + struct gnet_stats_queue cpu_qstats; /* 88 8 */
> int pad; /* 96 4 */
> refcount_t refcnt; /* 100 4 */
>
> /* XXX 24 bytes hole, try to pack */
>
> /* --- cacheline 2 boundary (128 bytes) --- */
>
> And:
>
> struct Qdisc {
> int (*enqueue)(struct sk_buff *skb,
> struct Qdisc *sch,
> struct sk_buff **to_free);
> struct sk_buff * (*dequeue)(struct Qdisc *sch);
> unsigned int flags;
> #define TCQ_F_BUILTIN 1
> #define TCQ_F_INGRESS 2
> #define TCQ_F_CAN_BYPASS 4
> #define TCQ_F_MQROOT 8
> #define TCQ_F_ONETXQUEUE 0x10 /* dequeue_skb() can assume all skbs are for
> * q->dev_queue : It can test
> * netif_xmit_frozen_or_stopped() before
> * dequeueing next packet.
> * Its true for MQ/MQPRIO slaves, or non
> * multiqueue device.
> */
> #define TCQ_F_WARN_NONWC (1 << 16)
> #define TCQ_F_CPUSTATS 0x20 /* run using percpu statistics */
> #define TCQ_F_NOPARENT 0x40 /* root of its hierarchy :
> * qdisc_tree_decrease_qlen() should stop.
> */
> #define TCQ_F_INVISIBLE 0x80 /* invisible by default in dump */
> #define TCQ_F_NOLOCK 0x100 /* qdisc does not require locking */
> #define TCQ_F_OFFLOADED 0x200 /* qdisc is offloaded to HW */
> u32 limit;
> const struct Qdisc_ops *ops;
> struct qdisc_size_table __rcu *stab;
> struct hlist_node hash;
> u32 handle;
> u32 parent;
>
> struct netdev_queue *dev_queue;
>
> struct net_rate_estimator __rcu *rate_est;
> struct gnet_stats_basic_sync __percpu *cpu_bstats;
> struct gnet_stats_queue __percpu *cpu_qstats;
> int pad;
> refcount_t refcnt;
>
>
> I'll try to fix now.

Ouch. The fields are annotated with type tags, which are ignored by gcc.
If this is not urgent I can debug it either later today or tomorrow.

>
> - Arnaldo
>
>
> > Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
> > ---
> > dwarves_fprintf.c | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
> > index e8399e7..1e6147a 100644
> > --- a/dwarves_fprintf.c
> > +++ b/dwarves_fprintf.c
> > @@ -572,6 +572,7 @@ static const char *__tag__name(const struct tag *tag, const struct cu *cu,
> > case DW_TAG_restrict_type:
> > case DW_TAG_atomic_type:
> > case DW_TAG_unspecified_type:
> > + case DW_TAG_LLVM_annotation:
> > type = cu__type(cu, tag->type);
> > if (type == NULL && tag->type != 0)
> > tag__id_not_found_snprintf(bf, len, tag->type);
> > @@ -786,6 +787,10 @@ next_type:
> > n = tag__has_type_loop(type, ptype, NULL, 0, fp);
> > if (n)
> > return printed + n;
> > + if (ptype->tag == DW_TAG_LLVM_annotation) {
> > + type = ptype;
> > + goto next_type;
> > + }
> > if (ptype->tag == DW_TAG_subroutine_type) {
> > printed += ftype__fprintf(tag__ftype(ptype),
> > cu, name, 0, 1,
> > @@ -880,6 +885,14 @@ print_modifier: {
> > else
> > printed += enumeration__fprintf(type, &tconf, fp);
> > break;
> > + case DW_TAG_LLVM_annotation: {
> > + struct tag *ttype = cu__type(cu, type->type);
> > + if (ttype) {
> > + type = ttype;
> > + goto next_type;
> > + }
> > + goto out_type_not_found;
> > + }
> > }
> > out:
> > if (type_expanded)
> > --
> > 2.39.1
> >
>