Em Wed, Feb 20, 2019 at 12:57:29PM -0800, Andrii Nakryiko escreveu:
> This patchset fixes the logic of determining bitfield_offsets and
> initial bit_offset when using BTF type information. It eliminates all
> the remaining discrepancies, when doing btfdiff on vmlinux image, module
> two instances of incorrectly reporting struct member type name when
> bitfield is the very first field in a struct, which is only happening
> when using DWARF data.
>
> Patch #1 makes btfdiff script easier to use during local development.
>
> Patch #2 fixes list of known base type names to handle clang-generated
> type descriptions better.
>
> Patch #3 fixes bitfield handling logic in btf_loader.
Thanks a lot! Applied.
And here I see no differences in my vmlinux:
[acme@quaco pahole]$ btfdiff vmlinux
[acme@quaco pahole]$
[acme@quaco pahole]$ perf stat pahole -F dwarf --flat_arrays --show_private_classes vmlinux > /tmp/dwarf
Performance counter stats for 'pahole -F dwarf --flat_arrays --show_private_classes vmlinux':
36,140.58 msec task-clock:u # 0.998 CPUs utilized
0 context-switches:u # 0.000 K/sec
0 cpu-migrations:u # 0.000 K/sec
359,238 page-faults:u # 0.010 M/sec
83,741,861,962 cycles:u # 2.317 GHz
99,851,434,338 instructions:u # 1.19 insn per cycle
20,974,798,749 branches:u # 580.367 M/sec
288,410,045 branch-misses:u # 1.38% of all branches
36.230455825 seconds time elapsed
35.037146000 seconds user
0.906593000 seconds sys
[acme@quaco pahole]$ perf stat pahole -F btf vmlinux > /tmp/btf
Performance counter stats for 'pahole -F btf vmlinux':
215.21 msec task-clock:u # 0.994 CPUs utilized
0 context-switches:u # 0.000 K/sec
0 cpu-migrations:u # 0.000 K/sec
3,195 page-faults:u # 0.015 M/sec
460,363,235 cycles:u # 2.139 GHz
546,688,575 instructions:u # 1.19 insn per cycle
104,488,443 branches:u # 485.522 M/sec
2,012,815 branch-misses:u # 1.93% of all branches
0.216609739 seconds time elapsed
0.200431000 seconds user
0.014834000 seconds sys
[acme@quaco pahole]$
[acme@quaco pahole]$ wc -l /tmp/dwarf
106101 /tmp/dwarf
[acme@quaco pahole]$ wc -l /tmp/btf
106101 /tmp/btf
[acme@quaco pahole]$
[acme@quaco pahole]$ pahole -F btf -C sk_buff_head vmlinux
struct sk_buff_head {
struct sk_buff * next; /* 0 8 */
struct sk_buff * prev; /* 8 8 */
__u32 qlen; /* 16 4 */
spinlock_t lock; /* 20 4 */
/* size: 24, cachelines: 1, members: 4 */
/* last cacheline: 24 bytes */
};
[acme@quaco pahole]$ pahole --expand_types -F btf -C sk_buff_head vmlinux
struct sk_buff_head {
struct sk_buff * next; /* 0 8 */
struct sk_buff * prev; /* 8 8 */
/* typedef __u32 */ unsigned int qlen; /* 16 4 */
/* typedef spinlock_t */ struct spinlock {
union {
struct raw_spinlock {
/* typedef arch_spinlock_t */ struct qspinlock {
union {
/* typedef atomic_t */ struct {
int counter; /* 20 4 */
} val; /* 20 4 */
struct {
/* typedef u8 -> __u8 */ unsigned char locked; /* 20 1 */
/* typedef u8 -> __u8 */ unsigned char pending; /* 21 1 */
}; /* 20 2 */
struct {
/* typedef u16 -> __u16 */ short unsigned int locked_pending; /* 20 2 */
/* typedef u16 -> __u16 */ short unsigned int tail; /* 22 2 */
}; /* 20 4 */
}; /* 20 4 */
} raw_lock; /* 20 4 */
} rlock; /* 20 4 */
}; /* 20 4 */
} lock; /* 20 4 */
/* size: 24, cachelines: 1, members: 4 */
/* last cacheline: 24 bytes */
};
[acme@quaco pahole]$
The problem with the packed structs is gone:
[acme@quaco pahole]$ pahole -F dwarf -C screen_info vmlinux > /tmp/dwarf
[acme@quaco pahole]$ pahole -F btf -C screen_info vmlinux > /tmp/btf
[acme@quaco pahole]$ diff -u /tmp/btf /tmp/dwarf
[acme@quaco pahole]$ pahole --hex -F btf -C screen_info vmlinux
struct screen_info {
__u8 orig_x; /* 0 0x1 */
__u8 orig_y; /* 0x1 0x1 */
__u16 ext_mem_k; /* 0x2 0x2 */
__u16 orig_video_page; /* 0x4 0x2 */
__u8 orig_video_mode; /* 0x6 0x1 */
__u8 orig_video_cols; /* 0x7 0x1 */
__u8 flags; /* 0x8 0x1 */
__u8 unused2; /* 0x9 0x1 */
__u16 orig_video_ega_bx; /* 0xa 0x2 */
__u16 unused3; /* 0xc 0x2 */
__u8 orig_video_lines; /* 0xe 0x1 */
__u8 orig_video_isVGA; /* 0xf 0x1 */
__u16 orig_video_points; /* 0x10 0x2 */
__u16 lfb_width; /* 0x12 0x2 */
__u16 lfb_height; /* 0x14 0x2 */
__u16 lfb_depth; /* 0x16 0x2 */
__u32 lfb_base; /* 0x18 0x4 */
__u32 lfb_size; /* 0x1c 0x4 */
__u16 cl_magic; /* 0x20 0x2 */
__u16 cl_offset; /* 0x22 0x2 */
__u16 lfb_linelength; /* 0x24 0x2 */
__u8 red_size; /* 0x26 0x1 */
__u8 red_pos; /* 0x27 0x1 */
__u8 green_size; /* 0x28 0x1 */
__u8 green_pos; /* 0x29 0x1 */
__u8 blue_size; /* 0x2a 0x1 */
__u8 blue_pos; /* 0x2b 0x1 */
__u8 rsvd_size; /* 0x2c 0x1 */
__u8 rsvd_pos; /* 0x2d 0x1 */
__u16 vesapm_seg; /* 0x2e 0x2 */
__u16 vesapm_off; /* 0x30 0x2 */
__u16 pages; /* 0x32 0x2 */
__u16 vesa_attributes; /* 0x34 0x2 */
__u32 capabilities; /* 0x36 0x4 */
__u32 ext_lfb_base; /* 0x3a 0x4 */
__u8 _reserved[2]; /* 0x3e 0x2 */
/* size: 64, cachelines: 1, members: 36 */
};
[acme@quaco pahole]$
And the definition in include/uapi/linux/screen_info.h is:
/*
* These are set up by the setup-routine at boot-time:
*/
struct screen_info {
__u8 orig_x; /* 0x00 */
__u8 orig_y; /* 0x01 */
__u16 ext_mem_k; /* 0x02 */
__u16 orig_video_page; /* 0x04 */
__u8 orig_video_mode; /* 0x06 */
__u8 orig_video_cols; /* 0x07 */
__u8 flags; /* 0x08 */
__u8 unused2; /* 0x09 */
__u16 orig_video_ega_bx;/* 0x0a */
__u16 unused3; /* 0x0c */
__u8 orig_video_lines; /* 0x0e */
__u8 orig_video_isVGA; /* 0x0f */
__u16 orig_video_points;/* 0x10 */
/* VESA graphic mode -- linear frame buffer */
__u16 lfb_width; /* 0x12 */
__u16 lfb_height; /* 0x14 */
__u16 lfb_depth; /* 0x16 */
__u32 lfb_base; /* 0x18 */
__u32 lfb_size; /* 0x1c */
__u16 cl_magic, cl_offset; /* 0x20 */
__u16 lfb_linelength; /* 0x24 */
__u8 red_size; /* 0x26 */
__u8 red_pos; /* 0x27 */
__u8 green_size; /* 0x28 */
__u8 green_pos; /* 0x29 */
__u8 blue_size; /* 0x2a */
__u8 blue_pos; /* 0x2b */
__u8 rsvd_size; /* 0x2c */
__u8 rsvd_pos; /* 0x2d */
__u16 vesapm_seg; /* 0x2e */
__u16 vesapm_off; /* 0x30 */
__u16 pages; /* 0x32 */
__u16 vesa_attributes; /* 0x34 */
__u32 capabilities; /* 0x36 */
__u32 ext_lfb_base; /* 0x3a */
__u8 _reserved[2]; /* 0x3e */
} __attribute__((packed));
Which ones where these: "module two instances of incorrectly reporting struct
member type name when bitfield is the very first field in a struct, which is
only happening when using DWARF data." ?
- Arnaldo
