dwarf_loader: Store the DW_AT_alignment if available
DWARF got a DW_AT_alignment as described in:
http://dwarfstd.org/ShowIssue.php?issue=140528.1
This appeared first in DWARF5:
http://dwarfstd.org/doc/DWARF5.pdf
In:
----------------------------------------------------------------------
Chapter 2.
General Description
2.24 Alignment
A debugging information entry may have a DW_AT_alignment attribute whose
value of class constant is a positive, non-zero, integer describing the
alignment of the entity.
For example, an alignment attribute whose value is 8 indicates that the
entity to which it applies occurs at an address that is a multiple of
eight (not a multiple of 8 or 256)
----------------------------------------------------------------------
Use it on a struct present in the running kernel, i.e. not specifying
which ELF file to look for the DWARF info to use:
$ pahole -C inet_timewait_death_row
struct inet_timewait_death_row {
atomic_t tw_count; /* 0 4 */
/* XXX 60 bytes hole, try to pack */
/* --- cacheline 1 boundary (64 bytes) --- */
struct inet_hashinfo * hashinfo __attribute__((__aligned__(64)); /* 64 8 */
int sysctl_max_tw_buckets; /* 72 4 */
/* size: 128, cachelines: 2, members: 3 */
/* sum members: 16, holes: 1, sum holes: 60 */
/* padding: 52 */
};
$
Now to do some tweaking to get that "__attribute..." part nicely, hum,
aligned in the pahole output :-)
BTW: the original struct is in the kernel sources:
include/net/netns/ipv4.h
struct inet_timewait_death_row {
atomic_t tw_count;
struct inet_hashinfo *hashinfo ____cacheline_aligned_in_smp;
int sysctl_max_tw_buckets;
};
Reported-by: Mark Wielaard <mark@klomp.org>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2 files changed
