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

Arnaldo Carvalho de Melo
2023-03-28T21:17:46Z

Em Tue, Mar 28, 2023 at 06:30:05PM +0300, Eduard Zingerman escreveu:
> On Tue, 2023-03-28 at 12:26 -0300, Arnaldo Carvalho de Melo wrote:
> [...]
> > Sure, but look:
> >
> > > > - struct qdisc_size_table * stab; /* 32 8 */
> > > > + struct qdisc_size_table stab; /* 32 8 */
> >
> > Its the DW_TAG_pointer_type that is getting lost somehow:
> >
> > <1><b0af32>: Abbrev Number: 81 (DW_TAG_structure_type)
> > <b0af33> DW_AT_name : (indirect string, offset: 0xe825): Qdisc
> > <b0af37> DW_AT_byte_size : 384
> > <b0af39> DW_AT_decl_file : 223
> > <b0af3a> DW_AT_decl_line : 72
> >
> > <SNIP>
> >
> > <2><b0af77>: Abbrev Number: 65 (DW_TAG_member)
> > <b0af78> DW_AT_name : (indirect string, offset: 0x4745ff): stab
> > <b0af7c> DW_AT_type : <0xb0b76b>
> > <b0af80> DW_AT_decl_file : 223
> > <b0af81> DW_AT_decl_line : 99
> > <b0af82> DW_AT_data_member_location: 32
> >
> > <SNIP>
> >
> > <1><b0b76b>: Abbrev Number: 61 (DW_TAG_pointer_type)
> > <b0b76c> DW_AT_type : <0xb0b77a>
> > <2><b0b770>: Abbrev Number: 62 (User TAG value: 0x6000)
> > <b0b771> DW_AT_name : (indirect string, offset: 0x378): btf_type_tag
> > <b0b775> DW_AT_const_value : (indirect string, offset: 0x6e93): rcu
> > <2><b0b779>: Abbrev Number: 0
> > <1><b0b77a>: Abbrev Number: 69 (DW_TAG_structure_type)
> > <b0b77b> DW_AT_name : (indirect string, offset: 0x6e5ed): qdisc_size_table
> > <b0b77f> DW_AT_byte_size : 64
> > <b0b780> DW_AT_decl_file : 223
> > <b0b781> DW_AT_decl_line : 56
> >
> >
> > So it's all there in the DWARF info:
> >
> > b0af77 has type 0xb0b76b which is a DW_TAG_pointer_type that has type
> > 0xb0b77a, that is DW_TAG_structure_type.
> >
> > Now lets see how this was encoded into BTF:
> >
> > [4725] STRUCT 'Qdisc' size=384 vlen=28
> > <SNIP>
> > 'stab' type_id=4790 bits_offset=256
> > <SNIP>
> > [4790] PTR '(anon)' type_id=4789
> > <SNIP>
> > [4789] TYPE_TAG 'rcu' type_id=4791
> > <SNIP>
> > [4791] STRUCT 'qdisc_size_table' size=64 vlen=5
> > 'rcu' type_id=320 bits_offset=0
> > 'list' type_id=87 bits_offset=128
> > 'szopts' type_id=4792 bits_offset=256
> > 'refcnt' type_id=16 bits_offset=448
> > 'data' type_id=4659 bits_offset=480
> >
> > So it all seems ok, we should keep all the info and teach fprintf to
> > handle TYPE_TAG.
> >
> > Which you tried, but somehow the '*' link is missing.
>
> Yep, thanks a lot for the analysis, I will take a look.
> Hopefully will send v2 tomorrow.

So, with the patch below it gets equivalent, but some more tweaking is
needed to make the output completely match (spaces, "long usigned" ->
"unsigned long", which seems to be all equivalent):

--- /tmp/gcc 2023-03-28 18:13:42.022385428 -0300
+++ /tmp/clang 2023-03-28 18:13:45.854486885 -0300
@@ -73,15 +73,15 @@
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 */

@@ -96,8 +96,8 @@

/* XXX 4 bytes hole, try to pack */

- long unsigned int state; /* 216 8 */
- long unsigned int state2; /* 224 8 */
+ unsigned long state; /* 216 8 */
+ unsigned long state2; /* 224 8 */
struct Qdisc * next_sched; /* 232 8 */
struct sk_buff_head skb_bad_txq; /* 240 24 */

@@ -112,7 +112,7 @@
/* XXX 40 bytes hole, try to pack */

/* --- cacheline 6 boundary (384 bytes) --- */
- long int privdata[]; /* 384 0 */
+ long privdata[]; /* 384 0 */

/* size: 384, cachelines: 6, members: 28 */
/* sum members: 260, holes: 4, sum holes: 124 */
@@ -145,19 +145,19 @@
/* XXX 4 bytes hole, try to pack */

struct netdev_queue * (*select_queue)(struct Qdisc *, struct tcmsg *); /* 8 8 */
- int (*graft)(struct Qdisc *, long unsigned int, struct Qdisc *, struct Qdisc * *, struct netlink_ext_ack *); /* 16 8 */
+ int (*graft)(struct Qdisc *, unsigned long, struct Qdisc *, struct Qdisc * *, struct netlink_ext_ack *); /* 16 8 */
- struct Qdisc * (*leaf)(struct Qdisc *, long unsigned int); /* 24 8 */
+ struct Qdisc * (*leaf)(struct Qdisc *, unsigned long); /* 24 8 */
- void (*qlen_notify)(struct Qdisc *, long unsigned int); /* 32 8 */
+ void (*qlen_notify)(struct Qdisc *, unsigned long); /* 32 8 */
- long unsigned int (*find)(struct Qdisc *, u32); /* 40 8 */
+ unsigned long (*find)(struct Qdisc *, u32); /* 40 8 */
- int (*change)(struct Qdisc *, u32, u32, struct nlattr * *, long unsigned int *, struct netlink_ext_ack *); /* 48 8 */
+ int (*change)(struct Qdisc *, u32, u32, struct nlattr * *, unsigned long *, struct netlink_ext_ack *); /* 48 8 */
- int (*delete)(struct Qdisc *, long unsigned int, struct netlink_ext_ack *); /* 56 8 */
+ int (*delete)(struct Qdisc *, unsigned long, struct netlink_ext_ack *); /* 56 8 */

diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
index 1e6147a82056c188..1ecc24321bf8f975 100644
--- a/dwarves_fprintf.c
+++ b/dwarves_fprintf.c
@@ -788,8 +788,15 @@ next_type:
if (n)
return printed + n;
if (ptype->tag == DW_TAG_LLVM_annotation) {
- type = ptype;
- goto next_type;
+ // FIXME: Just skip this for now, we need to print this annotation
+ // to match the original source code.
+
+ if (ptype->type == 0) {
+ printed += fprintf(fp, "%-*s %s", tconf.type_spacing, "void *", name);
+ break;
+ }
+
+ ptype = cu__type(cu, ptype->type);
}
if (ptype->tag == DW_TAG_subroutine_type) {
printed += ftype__fprintf(tag__ftype(ptype),