perf annotate-data: Set bitfield member offset and size properly

The bitfield members might not have DW_AT_data_member_location.  Let's
use DW_AT_data_bit_offset to set the member offset correct.  Also use
DW_AT_bit_size for the name like in a C program.

Before:
  Annotate type: 'struct sk_buff' (1 samples)
        Percent     Offset       Size  Field
  -      100.00          0        232  struct sk_buff {
  +        0.00          0         24      union  ;
  +        0.00         24          8      union  ;
  +        0.00         32          8      union  ;
           0.00         40         48      char[] cb;
  +        0.00         88         16      union  ;
           0.00        104          8      long unsigned int      _nfct;
         100.00        112          4      unsigned int   len;
           0.00        116          4      unsigned int   data_len;
           0.00        120          2      __u16  mac_len;
           0.00        122          2      __u16  hdr_len;
           0.00        124          2      __u16  queue_mapping;
           0.00        126          0      __u8[] __cloned_offset;
           0.00          0          1      __u8   cloned;
           0.00          0          1      __u8   nohdr;
           0.00          0          1      __u8   fclone;
           0.00          0          1      __u8   peeked;
           0.00          0          1      __u8   head_frag;
           0.00          0          1      __u8   pfmemalloc;
           0.00          0          1      __u8   pp_recycle;
           0.00        127          1      __u8   active_extensions;
  +        0.00        128         60      union  ;
           0.00        188          4      sk_buff_data_t tail;
           0.00        192          4      sk_buff_data_t end;
           0.00        200          8      unsigned char* head;

After:

  Annotate type: 'struct sk_buff' (1 samples)
        Percent     Offset       Size  Field
  -      100.00          0        232  struct sk_buff {
  +        0.00          0         24      union  ;
  +        0.00         24          8      union  ;
  +        0.00         32          8      union  ;
           0.00         40         48      char[] cb
  +        0.00         88         16      union  ;
           0.00        104          8      long unsigned int      _nfct;
         100.00        112          4      unsigned int   len;
           0.00        116          4      unsigned int   data_len;
           0.00        120          2      __u16  mac_len;
           0.00        122          2      __u16  hdr_len;
           0.00        124          2      __u16  queue_mapping;
           0.00        126          0      __u8[] __cloned_offset;
           0.00        126          1      __u8   cloned:1;
           0.00        126          1      __u8   nohdr:1;
           0.00        126          1      __u8   fclone:2;
           0.00        126          1      __u8   peeked:1;
           0.00        126          1      __u8   head_frag:1;
           0.00        126          1      __u8   pfmemalloc:1;
           0.00        126          1      __u8   pp_recycle:1;
           0.00        127          1      __u8   active_extensions;
  +        0.00        128         60      union  ;
           0.00        188          4      sk_buff_data_t tail;
           0.00        192          4      sk_buff_data_t end;
           0.00        200          8      unsigned char* head;

Commiter notes:

Collect some data:

  root@number:~# perf mem record -a --ldlat 5 -- ping -s 8193 -f 192.168.86.1
  Memory events are enabled on a subset of CPUs: 16-27
  PING 192.168.86.1 (192.168.86.1) 8193(8221) bytes of data.
  .^C
  --- 192.168.86.1 ping statistics ---
  13881 packets transmitted, 13880 received, 0.00720409% packet loss, time 8664ms
  rtt min/avg/max/mdev = 0.510/0.599/7.768/0.115 ms, ipg/ewma 0.624/0.593 ms
  [ perf record: Woken up 8 times to write data ]
  [ perf record: Captured and wrote 14.877 MB perf.data (46785 samples) ]

  root@number:~#
  root@number:~# perf evlist
  cpu_atom/mem-loads,ldlat=5/P
  cpu_atom/mem-stores/P
  dummy:u
  root@number:~# perf evlist -v
  cpu_atom/mem-loads,ldlat=5/P: type: 10 (cpu_atom), size: 136, config: 0x5d0 (mem-loads), { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|ADDR|CPU|PERIOD|IDENTIFIER|DATA_SRC|WEIGHT_STRUCT, read_format: ID|LOST, disabled: 1, inherit: 1, freq: 1, precise_ip: 3, sample_id_all: 1, { bp_addr, config1 }: 0x7
  cpu_atom/mem-stores/P: type: 10 (cpu_atom), size: 136, config: 0x6d0 (mem-stores), { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|ADDR|CPU|PERIOD|IDENTIFIER|DATA_SRC|WEIGHT_STRUCT, read_format: ID|LOST, disabled: 1, inherit: 1, freq: 1, precise_ip: 3, sample_id_all: 1
  dummy:u: type: 1 (software), size: 136, config: 0x9 (PERF_COUNT_SW_DUMMY), { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|ADDR|CPU|IDENTIFIER|DATA_SRC|WEIGHT_STRUCT, read_format: ID|LOST, inherit: 1, exclude_kernel: 1, exclude_hv: 1, mmap: 1, comm: 1, task: 1, mmap_data: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
  root@number:~#

Ok, now lets see what changes from before this patch to after it:

  root@number:~# perf annotate --data-type > /tmp/before

Apply the patch, build:

  root@number:~# perf annotate --data-type > /tmp/after

The first hunk of the diff, for a glib data structure, in userspace,
look at those bitfields:

  root@number:~# diff -u10 /tmp/before /tmp/after | head -20
  --- /tmp/before	2024-08-20 17:29:58.306765780 -0300
  +++ /tmp/after	2024-08-20 17:33:13.210582596 -0300
  @@ -163,22 +163,22 @@

   Annotate type: 'GHashTable' in /usr/lib64/libglib-2.0.so.0.8000.3 (1 samples):
   ============================================================================
    Percent     offset       size  field
     100.00          0         96  GHashTable	 {
       0.00          0          8      gsize	size;
       0.00          8          4      gint	mod;
     100.00         12          4      guint	mask;
       0.00         16          4      guint	nnodes;
       0.00         20          4      guint	noccupied;
  -    0.00          0          4      guint	have_big_keys;
  -    0.00          0          4      guint	have_big_values;
  +    0.00         24          1      guint	have_big_keys:1;
  +    0.00         24          1      guint	have_big_values:1;
       0.00         32          8      gpointer	keys;
       0.00         40          8      guint*	hashes;
       0.00         48          8      gpointer	values;
  root@number:~#

As advertised :-)

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240815223823.2402285-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 28 insertions, 6 deletions

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index aa330c7d8edd..e5589268cb42 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -202,7 +202,7 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
 	struct annotated_member *parent = arg;
 	struct annotated_member *member;
 	Dwarf_Die member_type, die_mem;
-	Dwarf_Word size, loc;
+	Dwarf_Word size, loc, bit_size = 0;
 	Dwarf_Attribute attr;
 	struct strbuf sb;
 	int tag;
@@ -226,15 +226,37 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
 	if (dwarf_aggregate_size(&die_mem, &size) < 0)
 		size = 0;
 
-	if (!dwarf_attr_integrate(die, DW_AT_data_member_location, &attr))
-		loc = 0;
-	else
+	if (dwarf_attr_integrate(die, DW_AT_data_member_location, &attr))
 		dwarf_formudata(&attr, &loc);
+	else {
+		/* bitfield member */
+		if (dwarf_attr_integrate(die, DW_AT_data_bit_offset, &attr) &&
+		    dwarf_formudata(&attr, &loc) == 0)
+			loc /= 8;
+		else
+			loc = 0;
+
+		if (dwarf_attr_integrate(die, DW_AT_bit_size, &attr) &&
+		    dwarf_formudata(&attr, &bit_size) == 0)
+			size = (bit_size + 7) / 8;
+	}
 
 	member->type_name = strbuf_detach(&sb, NULL);
 	/* member->var_name can be NULL */
-	if (dwarf_diename(die))
-		member->var_name = strdup(dwarf_diename(die));
+	if (dwarf_diename(die)) {
+		if (bit_size) {
+			if (asprintf(&member->var_name, "%s:%ld",
+				     dwarf_diename(die), (long)bit_size) < 0)
+				member->var_name = NULL;
+		} else {
+			member->var_name = strdup(dwarf_diename(die));
+		}
+
+		if (member->var_name == NULL) {
+			free(member);
+			return DIE_FIND_CB_END;
+		}
+	}
 	member->size = size;
 	member->offset = loc + parent->offset;
 	INIT_LIST_HEAD(&member->children);