Question

我有一个无法提供正确输出的图书馆。我想这可能是写入违规，并将其集中在这段代码上：

void Page::build_default_frame(PosType genome_display_length)
{
    Frame* frame = new Frame(*this,
                             margin_left,
                             margin_top,
                             width - margin_left - margin_right,
                             genome_display_length);
    default_frame = frame;
    frames.insert(default_frame);
}

default_frame是一个提升intrusive_ptr<Frame>。

在执行句子default_frame = frame之前，对象frame的内容是正确的，但在此之后，其内容被修改为奇怪的值。所以我在frame object：

的两个成员变量上设置了两个监视

(gdb) watch -l frame->genome_scale.genome_display_length 
Hardware watchpoint 4: -location frame->genome_scale.genome_display_length
(gdb) watch -l frame->genome_scale.frame_width 
Hardware watchpoint 5: -location frame->genome_scale.frame_width

然后继续。它突然报告这些地址的写操作：

(gdb) c
Continuing.
Hardware watchpoint 4: -location frame->genome_scale.genome_display_length

Old value = 1000
New value = 16
_dl_runtime_resolve () at ../sysdeps/x86_64/dl-trampoline.S:39
39  ../sysdeps/x86_64/dl-trampoline.S: No such file or directory.
(gdb) bt
#0  _dl_runtime_resolve () at ../sysdeps/x86_64/dl-trampoline.S:39
#1  0x00007ffff7b93dd0 in geno_eye::Page::build_default_frame (this=0x6071b0, genome_display_length=1000)
    at /home/yangxi/projects/GenoEye/src/geno_eye/Page.cpp:127
#2  0x00007ffff7b93cc1 in geno_eye::Page::Page (this=0x6071b0, context=0x607750, width=300, height=300, 
    genome_display_length=1000) at /home/yangxi/projects/GenoEye/src/geno_eye/Page.cpp:29
#3  0x00000000004016b8 in geno_eye::__tester__::run (this=0x7fffffffe1c8)
    at /home/yangxi/projects/GenoEye/t/t_page.cpp:15
#4  0x00000000004015d1 in main () at /home/yangxi/projects/GenoEye/t/t_page.cpp:36
(gdb) c
Continuing.
Hardware watchpoint 5: -location frame->genome_scale.frame_width

Old value = 240
New value = 3.1228427039313504e-317
_dl_runtime_resolve () at ../sysdeps/x86_64/dl-trampoline.S:40
40  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) bt
#0  _dl_runtime_resolve () at ../sysdeps/x86_64/dl-trampoline.S:40
#1  0x00007ffff7b93dd0 in geno_eye::Page::build_default_frame (this=0x6071b0, genome_display_length=1000)
    at /home/yangxi/projects/GenoEye/src/geno_eye/Page.cpp:127
#2  0x00007ffff7b93cc1 in geno_eye::Page::Page (this=0x6071b0, context=0x607750, width=300, height=300, 
    genome_display_length=1000) at /home/yangxi/projects/GenoEye/src/geno_eye/Page.cpp:29
#3  0x00000000004016b8 in geno_eye::__tester__::run (this=0x7fffffffe1c8)
    at /home/yangxi/projects/GenoEye/t/t_page.cpp:15
#4  0x00000000004015d1 in main () at /home/yangxi/projects/GenoEye/t/t_page.cpp:36

两个旧值是这两个成员变量的正确值。这个写操作是在执行boost intrusive_ptr的=函数之前发生的，因为我按了几十个＆＃34; next＆＃34;，代码仍在文件 dl-trampoline.S

(gdb) n
41  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
42  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
43  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
44  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
45  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
46  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
47  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
48  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
49  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
50  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
51  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
52  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
53  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
54  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
56  in ../sysdeps/x86_64/dl-trampoline.S
(gdb) n
boost::intrusive_ptr<geno_eye::Frame>::operator= (this=0x6071b0, rhs=0x3e8)
    at /usr/include/boost/smart_ptr/intrusive_ptr.hpp:134
134     {

什么是 dl-trampoline.S ？为什么它静静地写在我的对象的记忆中？

除此之外，我还运行valgrind：

$ valgrind ./t_page

但是，它会报告对该对象的无效读取，而不是无效写入，这是在对象创建完成后发生的。

Answer 1

这是由引用堆栈错误引起的。

对象genome_scale包含对frame对象的两个成员变量的两个引用。当我重构我的代码时，它意外地引用了两个堆栈变量...

所以，也许我应该避免在这种情况下使用引用类型，因为你可以轻松地向它们提供堆栈内容并且不会收到任何警告。

对我的变量进行神秘的写入违规

1 个答案: