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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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.

- 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
> 

-- 

- Arnaldo