windbg使用qt4.natvis

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用windbg调试QT程序或者分析QT程序的dump是一件痛苦的事情,因为windbg缺少对QT基础数据的展示能力,比如:

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int main(int argc, char *argv[])
{
QString str = "hello world";
QList<QString> str_list;
str_list.append(str);
QMap<int, QString> str_map;
str_map[11] = str;
}

这份代码使用windbg查看str,str_list或者str_map简直是一件折磨的事情。

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0:000> dv
argc = 0n1
argv = 0x02cc5e00
str = class QString
str_list = class QList<QString>
str_map = class QMap<int,QString>
a = class QApplication
w = class QMsgTest
0:000> dx str
str [Type: QString]
[+0x000] d : 0x2cc5d80 [Type: QString::Data *]
0:000> dx str_list
str_list [Type: QList<QString>]
[+0x000] p [Type: QListData]
[+0x000] d : 0x2cc7258 [Type: QListData::Data *]
0:000> dx str_map
str_map [Type: QMap<int,QString>]
[+0x000] d : 0x2cc72b8 [Type: QMapData *]
[+0x000] e : 0x2cc72b8 [Type: QMapData::Node *]

可以看到,windbg只会告诉你类型,根本不会给你展示数据本身,如果要查看数据还得自己来算,以最复杂的QMap为例:

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0:000> ?? str_map.d->forward[0]
struct QMapData * 0x031470f8
+0x000 backward : 0x03147068 QMapData
+0x004 forward : [12] 0x03147068 QMapData
+0x034 ref : QBasicAtomicInt
+0x038 topLevel : 0n-17891602
+0x03c size : 0n-17891602
+0x040 randomBits : 0xfeeefeee
+0x044 insertInOrder : 0y0
+0x044 sharable : 0y1
+0x044 strictAlignment : 0y1
+0x044 reserved : 0y11111110111011101111111011101 (0x1fdddfdd)

0:000> ?? sizeof(@!"qtmsgtest!QMapPayloadNode<int,QString>")-sizeof(qtmsgtest!QMapData::Node*)
unsigned int 8

0:000> dt qtmsgtest!QMapNode<int,QString> (0x31470f8-8)
+0x000 key : 0n11
+0x004 value : QString
+0x008 backward : 0x03147068 QMapData::Node
+0x00c forward : [1] 0x03147068 QMapData::Node

0:000> ?? ((qtmsgtest!QString*)0x31470f4)->d
struct QString::Data * 0x03145b30
+0x000 ref : QBasicAtomicInt
+0x004 alloc : 0n11
+0x008 size : 0n11
+0x00c data : 0x03145b42 -> 0x68
+0x010 clean : 0y0
+0x010 simpletext : 0y0
+0x010 righttoleft : 0y0
+0x010 asciiCache : 0y0
+0x010 capacity : 0y0
+0x010 reserved : 0y11001101110 (0x66e)
+0x012 array : [1] 0x68

0:000> du @@C++(((qtmsgtest!QString*)0x31470f4)->d->data)
03145b42 "hello world"

你们看,为了获取key=11、value=”hello world”需要这么折腾一通,如果数据多了那不得抓狂。

不过幸运了是windbg现在支持natvis了,简单的说就是通过natvis里的配置自动解析和符号匹配的数据结构。接下来要做的就是找一个好用的qt的natvis了。我这里找了一个qt配合vs2012里的qt4.natvis,让我们看看加载后的效果:

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0:000> .nvload qt4.natvis
Successfully loaded visualizers in "C:\Program Files (x86)\Windows Kits\10\Debuggers\x86\Visualizers\qt4.natvis"
0:000> dv
argc = 0n1
argv = 0x02cc5e00
str = hello world
str_list = { size = 1 }
str_map = { size = 1 }
a = class QApplication
w = class QMsgTest
0:000> dx str
str : hello world [Type: QString]
[<Raw View>] [Type: QString]
[size] : 11 [Type: int]
[referenced] : 3 [Type: long]
[0] : 0x68 [Type: unsigned short]
[1] : 0x65 [Type: unsigned short]
[2] : 0x6c [Type: unsigned short]
[3] : 0x6c [Type: unsigned short]
[4] : 0x6f [Type: unsigned short]
[5] : 0x20 [Type: unsigned short]
[6] : 0x77 [Type: unsigned short]
[7] : 0x6f [Type: unsigned short]
[8] : 0x72 [Type: unsigned short]
[9] : 0x6c [Type: unsigned short]
[10] : 0x64 [Type: unsigned short]
0:000> dx str_list
str_list : { size = 1 } [Type: QList<QString>]
[<Raw View>] [Type: QList<QString>]
[referenced] : 1 [Type: long]
[0x0] : hello world [Type: QString]
0:000> dx str_map
str_map : { size = 1 } [Type: QMap<int,QString>]
[<Raw View>] [Type: QMap<int,QString>]
[referenced] : 1 [Type: long]
[0x0] : 0x2cc7340 : (11, hello world) [Type: QMapNode<int,QString> *]

看到了么,无论是str,str_list还是str_map都直接打印出了内部的数据,无需大费周章的折腾,这简直是windbg爱好者调试qt程序的神器。

最后附上qt4.natvis的地址:https://gist.github.com/gregseth/9bcd0112f8492fa7bfe7

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