如何获取内部值以用作 gdb 漂亮打印的数组？

Question

我为 InnerStruct 编写了一个漂亮的打印机，它将数组显示为 2 个元素和正确的值。我还为 TestStruct2 开了个玩笑，但是我不知道如何让 TestStruct 包含与 InnerStruct 相同的内容。我不知道如何从 gdb/python 访问 array.nestedVariables。我该如何编写才能让 TestStruct 给出与 InnerStruct 相同的结果？

来源

struct InnerStruct
{
    int buffer[100];
    int len;
};
struct TestStruct
{
    InnerStruct array;
};
struct TestStruct2
{
    InnerStruct array;
};

int main() {
    TestStruct s;
    s.array.buffer[0] = 5;
    s.array.buffer[1] = 8;
    s.array.len=2;
    TestStruct2 s2;
    s2.array.buffer[0] = 5;
    s2.array.buffer[1] = 8;
    s2.array.len=2;
    return 0;
}

.gdbinit

python

pp = gdb.printing.RegexpCollectionPrettyPrinter("pp")

class InnerStructPrinter:
    "Print a InnerStruct"

    class _iterator:
        def __init__ (self, start, finish):
            self.item = start
            self.finish = finish
            self.count = 0

        def __iter__ (self):
            return self

        def __next__ (self):
            count = self.count
            self.count = self.count + 1
            if self.item == self.finish:
                raise StopIteration
            elt = self.item.dereference()
            self.item = self.item + 1
            return ('[%d]' % count, elt)

        def next (self):
            return self.__next__()

    def __init__ (self, val):
        self.val = val

    def children (self):
        start = self.val['buffer'][0].address
        return self._iterator(start, start + self.val['len'])

    def to_string (self):
        len = self.val['len']
        return '%s of length %d' % (self.val.type, len)

    def display_hint (self):
        return 'array'

pp.add_printer('InnerStruct', '^InnerStruct$', InnerStructPrinter)

class TestStruct2Printer:
    "Print a TestStruct2"

    def __init__ (self, val):
        self.val = val

    def to_string (self):
        return "Array of"

    def children(self):
        yield ('0', 'fake')
        yield ('1', 'val')

    def display_hint (self):
        return 'array'

pp.add_printer('TestStruct2', '^TestStruct2$', TestStruct2Printer)

gdb.printing.register_pretty_printer(gdb.current_objfile(), pp)
end

Answer 1

我看不出添加这个还不够的原因。

class TestStructPrinter(InnerStructPrinter):
    def __init__(self, val):
        super().__init__(val['array'])

pp.add_printer('TestStruct', '^TestStruct$', TestStructPrinter)

换句话说，子字段的访问方式很简单val['field']['subfield']。子类化有点像 hack，但你明白了。

示例会话：

(gdb) show version 
GNU gdb (Debian 9.2-1) 9.2
Copyright (C) 2020 Free Software Foundation, Inc.
[…]
(gdb) python print(sys.version)
3.8.6 (default, Sep 25 2020, 09:36:53) 
[GCC 10.2.0]
(gdb) print s
 = InnerStruct of length 2 = {5, 8}
(gdb) print s.array
 = InnerStruct of length 2 = {5, 8}

不过，这似乎是一件相当愚蠢的事情：调试器应该可以帮助您区分类型。通过使 TestStruct 和 InnerStruct 打印出相同的内容，它反而会误导用户认为正在使用一种类型而不是另一种，并让他们尝试访问，比如说，s.buffer而不是 s.array.buffer.

如何获取内部值以用作 gdb 漂亮打印的数组？

How do I get the inner value to use as an array for gdb pretty print?

python

gdb

pretty-print