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

[Eduard Zingerman <eddyz87@gmail.com>]

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
> > 
>