gdb打印结构体member offset

linux的crash有个好处就是可以方便打印结构体成员变量的offset, 有时候对汇编的时候, 需要偏移, 可惜crash需要一个活体才行, 不能单纯的vmlinux, 因为它就是这么设计的

gdb天生没有这个功能, 不过python可以实现

cat offset.py
import gdb

class Offsets(gdb.Command):

def __init__(self):
    super (Offsets, self).__init__ ('offsets-of', gdb.COMMAND_DATA)

def invoke(self, arg, from_tty):
    argv = gdb.string_to_argv(arg)
    if len(argv) != 1:
        raise gdb.GdbError('offsets-of takes exactly 1 argument.')

    stype = gdb.lookup_type('struct %s' % argv[0])

    print argv[0], '{'
    for field in stype.fields():
        print '    [0x%x] %s' % (field.bitpos//8, field.name)
    print '}'

Offsets()

gdb vmlinux -x ~/offset.py
(gdb) offsets-of task_struct
task_struct {

[0x0] thread_info
[0x8] state
[0x10] stack
[0x18] usage
[0x1c] flags
[0x20] ptrace
[0x28] wake_entry
[0x30] on_cpu
[0x34] cpu
[0x38] wakee_flips
[0x40] wakee_flip_decay_ts

其实还是挺方便的, 省得用0指针来转

从这里来
https://stackoverflow.com/questions/9788679/how-to-get-the-relative-address-of-a-field-in-a-structure-dump-c