On 8/13/19 1:25 PM, Jens Axboe wrote:
> On 8/13/19 9:12 AM, Bart Van Assche wrote:
>> On 8/12/19 7:53 PM, Jens Axboe wrote:
>>> On 8/12/19 8:01 PM, Bart Van Assche wrote:
>>>> Instead of declaring the whole structure packed, only declare non-aligned
>>>> members packed. This patch is an alternative way to fix the following gcc 9
>>>> compiler warnings:
>>>>
>>>> eta.c: In function 'calc_thread_status':
>>>> eta.c:510:7: error: taking address of packed member of 'struct jobs_eta' may result in an unaligned pointer value [-Werror=address-of-packed-member]
>>>> 510 | je->rate);
>>>> | ~~^~~~~~
>>>> eta.c:522:66: error: taking address of packed member of 'struct jobs_eta' may result in an unaligned pointer value [-Werror=address-of-packed-member]
>>>> 522 | calc_rate(unified_rw_rep, disp_time, io_bytes, disp_io_bytes, je->rate);
>>>> | ~~^~~~~~
>>>> eta.c:523:64: error: taking address of packed member of 'struct jobs_eta' may result in an unaligned pointer value [-Werror=address-of-packed-member]
>>>> 523 | calc_iops(unified_rw_rep, disp_time, io_iops, disp_io_iops, je->iops);
>>>> |
>>>
>>> This seems fragile. Not that we change the struct all the time, or even often,
>>> but it'd be easy to add members and end up with different layout on 32-bit
>>> vs 64-bit.
>>>
>>> How do we improve on that?
>>
>> Hi Jens,
>>
>> Do you agree that the "BUILD_BUG_ON(sizeof(struct jobs_eta) != 160)"
>> statement added by the previous patch should catch such differences? 160
>> bytes namely is the size of an entirely packed jobs_eta structure.
>
> I guess that's good enough, though it'd be nice to check for holes
> explicitly. I wonder if there's an easy way to do that, though...
Hi Jens,
The pahole tool should be able to check for holes. Unfortunately that
tool doesn't seem to work very well on Ubuntu:
$ pahole -H 1 *.o
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x12d> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x175> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x58> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x15e> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x44> not handled!
die__process_function: tag not supported (INVALID)!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xb5> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xf2> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x48> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4cc> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x1ab> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4b6> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x736> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4ba> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x187> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4e4> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x42> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xd1> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xfd> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xaf> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x103> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x73> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xb5> not handled!
struct _IO_FILE {
int _flags; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
char * _IO_read_ptr; /* 8 8 */
char * _IO_read_end; /* 16 8 */
char * _IO_read_base; /* 24 8 */
char * _IO_write_base; /* 32 8 */
char * _IO_write_ptr; /* 40 8 */
char * _IO_write_end; /* 48 8 */
char * _IO_buf_base; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
char * _IO_buf_end; /* 64 8 */
char * _IO_save_base; /* 72 8 */
char * _IO_backup_base; /* 80 8 */
char * _IO_save_end; /* 88 8 */
struct _IO_marker * _markers; /* 96 8 */
struct _IO_FILE * _chain; /* 104 8 */
int _fileno; /* 112 4 */
int _flags2; /* 116 4 */
__off_t _old_offset; /* 120 8 */
/* --- cacheline 2 boundary (128 bytes) --- */
short unsigned int _cur_column; /* 128 2 */
signed char _vtable_offset; /* 130 1 */
char _shortbuf[1]; /* 131 1 */
/* XXX 4 bytes hole, try to pack */
_IO_lock_t * _lock; /* 136 8 */
__off64_t _offset; /* 144 8 */
struct _IO_codecvt * _codecvt; /* 152 8 */
struct _IO_wide_data * _wide_data; /* 160 8 */
struct _IO_FILE * _freeres_list; /* 168 8 */
void * _freeres_buf; /* 176 8 */
size_t __pad5; /* 184 8 */
/* --- cacheline 3 boundary (192 bytes) --- */
int _mode; /* 192 4 */
char _unused2[20]; /* 196 20 */
/* size: 216, cachelines: 4, members: 29 */
/* sum members: 208, holes: 2, sum holes: 8 */
/* last cacheline: 24 bytes */
};
struct fio_filelock {
uint32_t hash; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
struct fio_sem lock; /* 8 104 */
/* XXX last struct has 4 bytes of padding */
/* --- cacheline 1 boundary (64 bytes) was 48 bytes ago --- */
struct flist_head list; /* 112 16 */
/* --- cacheline 2 boundary (128 bytes) --- */
unsigned int references; /* 128 4 */
/* size: 136, cachelines: 3, members: 4 */
/* sum members: 128, holes: 1, sum holes: 4 */
/* padding: 4 */
/* paddings: 1, sum paddings: 4 */
/* last cacheline: 8 bytes */
};
struct io_u_ring {
unsigned int head; /* 0 4 */
unsigned int tail; /* 4 4 */
unsigned int max; /* 8 4 */
/* XXX 4 bytes hole, try to pack */
struct io_u * * ring; /* 16 8 */
/* size: 24, cachelines: 1, members: 4 */
/* sum members: 20, holes: 1, sum holes: 4 */
/* last cacheline: 24 bytes */
};
struct json_object {
struct json_pair * * pairs; /* 0 8 */
int pair_cnt; /* 8 4 */
/* XXX 4 bytes hole, try to pack */
struct json_value * parent; /* 16 8 */
/* size: 24, cachelines: 1, members: 3 */
/* sum members: 20, holes: 1, sum holes: 4 */
/* last cacheline: 24 bytes */
};
struct json_array {
struct json_value * * values; /* 0 8 */
int value_cnt; /* 8 4 */
/* XXX 4 bytes hole, try to pack */
struct json_value * parent; die__process_unit:
DW_TAG_restrict_type (0x37) @ <0x283> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xfc> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x14d> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x127> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xae> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4f> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4ba> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xda> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x552> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xa5> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xfb> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x59> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x72> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4ca> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xe5> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4ba> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xe5> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0xf6> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x5d> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x41> not handled!
die__process_unit: DW_TAG_restrict_type (0x37) @ <0x4c5> not handled!
/* 16 8 */
/* size: 24, cachelines: 1, members: 3 */
/* sum members: 20, holes: 1, sum holes: 4 */
/* last cacheline: 24 bytes */
};
struct json_value {
int type; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
union {
long long int integer_number; /* 8 */
double float_number; /* 8 */
char * string; /* 8 */
struct json_object * object; /* 8 */
struct json_array * array; /* 8 */
}; /* 8 8 */
int parent_type; /* 16 4 */
/* XXX 4 bytes hole, try to pack */
union {
struct json_pair * parent_pair; /* 8 */
struct json_array * parent_array; /* 8 */
}; /* 24 8 */
/* size: 32, cachelines: 1, members: 4 */
/* sum members: 24, holes: 2, sum holes: 8 */
/* last cacheline: 32 bytes */
};
Bart.
