To show just packed structs.
For instance, here are the top packed structures in the Linux kernel,
using BTF data:
$ pahole --packed --sizes | sort -k2 -nr | head
e820_table 64004 0
boot_params 4096 0
btrfs_super_block 3531 0
efi_variable 2084 0
ntb_info_regs 800 0
tboot 568 0
_legacy_mbr 512 0
disklabel 512 0
btrfs_root_item 439 0
saved_context 317 0
$
If you then look at:
$ pahole e820_table
struct e820_table {
__u32 nr_entries; /* 0 4 */
struct e820_entry entries[3200]; /* 4 64000 */
/* size: 64004, cachelines: 1001, members: 2 */
/* last cacheline: 4 bytes */
} __attribute__((__packed__));
$
In arch/x86/include/asm/e820/types.h we have:
/*
* The whole array of E820 entries:
*/
struct e820_table {
__u32 nr_entries;
struct e820_entry entries[E820_MAX_ENTRIES];
};
I.e. no explicit __packed__ attributes, but if we expand this a bit:
$ pahole -E e820_table
struct e820_table {
/* typedef __u32 */ unsigned int nr_entries; /* 0 4 */
struct e820_entry {
/* typedef u64 -> __u64 */ long long unsigned int addr; /* 4 8 */
/* typedef u64 -> __u64 */ long long unsigned int size; /* 12 8 */
enum e820_type type; /* 20 4 */
} __attribute__((__packed__)) entries[3200]; /* 4 64000 */
/* size: 64004, cachelines: 1001, members: 2 */
/* last cacheline: 4 bytes */
} __attribute__((__packed__));
$
We see that is that entries member that is packed, because:
$ pahole e820_entry
struct e820_entry {
u64 addr; /* 0 8 */
u64 size; /* 8 8 */
enum e820_type type; /* 16 4 */
/* size: 20, cachelines: 1, members: 3 */
/* last cacheline: 20 bytes */
} __attribute__((__packed__));
$
In arch/x86/include/asm/e820/types.h we have:
/*
* A single E820 map entry, describing a memory range of [addr...addr+size-1],
* of 'type' memory type:
*
* (We pack it because there can be thousands of them on large systems.)
*/
struct e820_entry {
u64 addr;
u64 size;
enum e820_type type;
} __attribute__((packed));
So yeah, it is there, BTF doesn't explicitly states it is packed (as
DWARF does) and pahole was able to infer that correctly.
Tested-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
cc3f9dce33