2.66 有调试符号的情况下在GDB中获取结构成员的偏移

https://scz.617.cn/unix/201203201430.txt

A: FatalError@stackoverflow 2012-03-20

How to get the relative address of a field in a structure dump - [2012-03-20]
https://stackoverflow.com/questions/9788679/how-to-get-the-relative-address-of-a-field-in-a-structure-dump-c

p/x &((struct some *)0)->member

从GDB 8.1开始可以用

ptype /o struct some

如果GDB支持Python，另有解决方案。

$ vi GetOffset.py

--------------------------------------------------------------------------
import gdb

class Offset ( gdb.Command ) :

    def __init__ (self ) :
        super( Offset, self ).__init__ ( 'offsetof', gdb.COMMAND_DATA )

    def invoke ( self, arg, from_tty ) :
        arg     = arg.strip()
        stype   = gdb.lookup_type( arg )
        # print( arg, '{' )
        print( "%s %s" % ( arg, '{' ) )
        for field in stype.fields() :
            print( '    %s => %#x' % ( field.name, field.bitpos // 8 ) )
        print( '}' )

Offset()
--------------------------------------------------------------------------

(gdb) source /tmp/GetOffset.py
(gdb) offsetof struct _zend_persistent_script
struct _zend_persistent_script {
    script => 0x0
    compiler_halt_offset => 0x148
    ping_auto_globals_mask => 0x150
    timestamp => 0x158
    corrupted => 0x160
    is_phar => 0x161
    mem => 0x168
    size => 0x170
    arena_mem => 0x178
    arena_size => 0x180
    dynamic_members => 0x188
}

在GDB中获取结构成员偏移有现实意义，考虑结构优化对齐对成员偏移的影响。