gdb-python :解析结构的每个字段并以适当的值打印它们(如果存在)

2022-01-20 00:00:00 python gdb coredump gdb-python

问题描述

我正在编写一个 python 脚本来自动从 gdb 调试核心转储.我正在尝试打印包含内核数据结构和列表的数据结构(例如 struct list_head).例如结构是这样的:

I am writing a python script to automate debugging core dump from gdb. i am trying to print data structure which includes kernel data structures and lists(e.g. struct list_head). For example the structure is something like this:

struct my_struct {
  struct my_hardware_context ahw;
  struct net_device *netdev;
  struct pci_dev *pdev;
  struct list_head mac_list;
  ....
  ....
};

我正在使用以下 API tp 打印此结构:

i am using following API tp print this structure:

gdb.execute('p (*(struct my_struct *)dev_base->priv)')

gdb.execute('p (*(struct my_struct *)dev_base->priv)')

所以我可以自动打印 'struct my_struct' 、 struct my_hardware_context ahw 的内容，但不能打印指针和列表的内容(例如 struct net_device *netdev、struct pci_dev *pdev、struct list_head mac_list)(只有地址是打印).那么如何使用gdb-python脚本打印*netdev、*pdev和mac_list的内容呢?

so i am able to print the content of 'struct my_struct' , struct my_hardware_context ahw, but not the content of pointers and list ( e.g. struct net_device *netdev, struct pci_dev *pdev, struct list_head mac_list) automatically (only address is printed). So how to print the content of *netdev, *pdev and mac_list using gdb-python script?

已让我的问题更清楚

我正在编写一个 python 脚本来自动从 gdb 调试核心转储.我正在尝试打印包含内核数据结构和列表的数据结构(例如 struct list_head).例如结构是这样的:

I am writing a python script to automate debugging core dump from gdb. i am trying to print data structure which includes kernel data structures and lists(e.g. struct list_head). For example the structure is something like this:

struct my_struct {
   struct my_hardware_context ahw;
   struct net_device *netdev;
   struct pci_dev *pdev;
   struct list_head mac_list;
   ....
   ....
};

我正在使用以下 API 来打印此结构:(可以假设我有正确的核心转储并添加了正确的符号.

i am using following API to print this structure: (it can be assumed that i have right core dump and added proper symbols.

main_struct = gdb.execute('p (*(struct my_struct *)dev_base->priv)')

打印 main_struct

现在它将打印 struct my_struct 的所有成员的值，但最多打印一级，这意味着它将打印 struct my_hardware_context ahw 的全部内容，因为它是一个实例，但它不会打印 struct net_device *netdev, struct 的内容pci_dev *pdev, struct list_head mac_list 等，所以现在我需要手动执行如下操作:

Now it will print the values of all members of struct my_struct but upto one level , meaning it will print the whole content of struct my_hardware_context ahw because it is an instance but it will not print the content of struct net_device *netdev, struct pci_dev *pdev, struct list_head mac_list etc. so now manually i need to do it like below:

netdev = gdb.parse_and_eval('*(*(struct my_struct *)dev_base->next->priv).netdev')

打印网络开发

pdev = gdb.parse_and_eval('*(*(struct my_struct *)dev_base->next->priv).pdev')

打印 pdev

所以我想自动化这些步骤.是否有任何 gdb-python API 或方法可以迭代 struct my_struct 并自动打印指针、数组和列表值?

so i want to automate these steps. Is there any gdb-python API or way by which it can iterate the struct my_struct and print the pointers, arrays and lists values also automatically?

谢谢.

解决方案

struct net_device, struct pci_dev 来自 Linux 的目的是供内核使用，而不是用户空间代码.它们甚至没有导出到您使用 make headers_install 获得的清理过的内核头文件中，以便与 libc 一起使用.

struct net_device, struct pci_dev from Linux are meant to be used by kernel and not userspace code. They're not even exported in the sanitized kernel headers you get with make headers_install for use with libc.

GDB 不能打印 struct net_device, struct pci_dev 因为它没有描述这些结构定义的调试信息.您的用户空间 struct my_struct 被声明为具有指向这些结构的不透明指针.我认为你一开始就不应该这样做.

GDB can't print struct net_device, struct pci_dev because it doesn't have debug info describing the definition of those structures. Your userspace struct my_struct is declared to have opaque pointers to those structures. I don't think you should be doing that in the first place.

诀窍是将调试信息从内核和驱动程序模块加载到 GDB:

The trick is loading debug info from both the kernel and your driver module into GDB:

  • 使用调试信息 (CONFIG_DEBUG_INFO) 获取内核.例如对于 Centos，从 http://debuginfo 获取匹配的 kernel-debuginfo 包.centos.org/6/x86_64/.
  • 通过检查 /sys/module/获取驱动程序模块的 .text、.data 和 .bss 加载地址MY-DRIVER/sections/{.text,.data,.bss} 来自在正常运行下运行驱动程序的系统.
  • Grab a kernel with debuginfo (CONFIG_DEBUG_INFO). e.g. for Centos, get the matching kernel-debuginfo package from http://debuginfo.centos.org/6/x86_64/.
  • Get the .text, .data and .bss load addresses of your driver module by inspecting /sys/module/MY-DRIVER/sections/{.text,.data,.bss} from a system running your driver under normal operation.

假设带有调试信息的内核位于 /usr/lib/debug/lib/modules/3.9.4-200.fc18.x86_64/vmlinux，运行:

Assuming the kernel with debug info is located at /usr/lib/debug/lib/modules/3.9.4-200.fc18.x86_64/vmlinux, run:

$ gdb /usr/lib/debug/lib/modules/3.9.4-200.fc18.x86_64/vmlinux vmcore
(gdb) add-symbol-file MY-DRIVER.ko TEXT-ADDR -s .data DATA-ADDR -s .bss BSS-ADDR

同时将 TEXT-ADDR、DATA-ADDR 和 BSS-ADDR 替换为/sys/module/下文件中的地址我的司机/sections/.(我认为在这种情况下，只是撒谎并使用地址 0 可能会起作用)

while replacing TEXT-ADDR, DATA-ADDR and BSS-ADDR with the address from the files under /sys/module/MY-DRIVER/sections/. (I think just lying and using an address of 0 would probably work in this case)

验证 ptype struct net_device、ptype struct pci_dev、ptype my_struct 是否有效.然后在获得 struct *my_struct 的地址之后，您应该能够打印其内容.

Verify that ptype struct net_device, ptype struct pci_dev, ptype my_struct work. Then after obtaining the address of a struct *my_struct the way you did before you should be able print its contents.

print-struct-follow-pointers.py

import gdb

def is_container(v):
    c = v.type.code
    return (c == gdb.TYPE_CODE_STRUCT or c == gdb.TYPE_CODE_UNION)

def is_pointer(v):
    return (v.type.code == gdb.TYPE_CODE_PTR)

def print_struct_follow_pointers(s, level_limit = 3, level = 0):
    indent = ' ' * level

    if not is_container(s):
        gdb.write('%s
' % (s,))
        return

    if level >= level_limit:
        gdb.write('%s { ... },
' % (s.type,))
        return

    gdb.write('%s {
' % (s.type,))
    for k in s.type.keys():
        v = s[k]
        if is_pointer(v):
            gdb.write('%s %s: %s' % (indent, k, v))
            try:
                v1 = v.dereference()
                v1.fetch_lazy()
            except gdb.error:
                gdb.write(',
')
                continue
            else:
                gdb.write(' -> ')
            print_struct_follow_pointers(v1, level_limit, level + 1)
        elif is_container(v):
            gdb.write('%s %s: ' % (indent, k))
            print_struct_follow_pointers(v, level_limit, level + 1)
        else:
            gdb.write('%s %s: %s,
' % (indent, k, v))
    gdb.write('%s},
' % (indent,))

class PrintStructFollowPointers(gdb.Command):
    '''
    print-struct-follow-pointers [/LEVEL_LIMIT] STRUCT-VALUE
    '''
    def __init__(self): 
        super(PrintStructFollowPointers, self).__init__(
            'print-struct-follow-pointers',
            gdb.COMMAND_DATA, gdb.COMPLETE_SYMBOL, False)

    def invoke(self, arg, from_tty):
        s = arg.find('/')
        if s == -1:
            (expr, limit) = (arg, 3)
        else:
            if arg[:s].strip():
                (expr, limit) = (arg, 3)
            else:
                i = s + 1
                for (i, c) in enumerate(arg[s+1:], s + 1):
                    if not c.isdigit():
                        break
                end = i
                digits = arg[s+1:end]
                try:
                    limit = int(digits)
                except ValueError:
                    raise gdb.GdbError(PrintStructFollowPointers.__doc__)
                (expr, limit) = (arg[end:], limit)
        try:
            v = gdb.parse_and_eval(expr)
        except gdb.error, e:
            raise gdb.GdbError(e.message)

        print_struct_follow_pointers(v, limit)

PrintStructFollowPointers()

示例会话

(gdb) source print-struct-follow-pointers.py
(gdb) print-struct-follow-pointers *p

您可以限制打印的嵌入结构的级别:

You can limit the levels of embedded structures printed:

(gdb) print-struct-follow-pointers/4 *p

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