visual-studio 当内存位置的内容改变或被读取时自动中断
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Automatic break when contents of a memory location changes or is read
提问by Matt Price
The old DEC Tru64 UNIX debugger had a feature (called "watchpoints to monitor variables") that would watch a memory location (or range of addresses) for read or write activity and when it detected such activity would break the program so you could investigate why. See for details:
旧的 DEC Tru64 UNIX 调试器有一个功能（称为“监视变量的观察点”），可以监视内存位置（或地址范围）的读或写活动，当检测到此类活动时会破坏程序，因此您可以调查原因. 详情请参阅：
http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/V50_HTML/ARH9QATE/DOCU_009.HTM
http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/V50_HTML/ARH9QATE/DOCU_009.HTM
Is there any way to do this sort of thing in the VisualStudio debugger? Or is there an add-on or some other tool that can do this under Windows?
有没有办法在 VisualStudio 调试器中做这种事情？或者是否有可以在 Windows 下执行此操作的附加组件或其他工具？
回答by Matt Price
Yeah, you can do this in visual studio. You can create a "New Data Breakpoint" under the debug menu while you're broken in a running program. You then specify the address to watch and the number of bytes.
是的，您可以在 Visual Studio 中执行此操作。当您在运行的程序中出现故障时，您可以在调试菜单下创建一个“新数据断点”。然后指定要监视的地址和字节数。
This only works for changing the value. I don't know how to watch for read access. However it's a very common question to want to know where a value got changed. I find that I don't want to know who reads a value as often.
这仅适用于更改值。我不知道如何观看读取访问。然而，想知道值在哪里改变是一个非常常见的问题。我发现我不想知道谁经常读取值。
回答by Kirill V. Lyadvinsky
Visual Studio allows to setbreakpoints on memory location only 4 bytes length (on 32-bit Windows version). To catch memory access (read or write) you could use the following class:
Visual Studio允许在仅 4 字节长度的内存位置上设置断点（在 32 位 Windows 版本上）。要捕获内存访问（读取或写入），您可以使用以下类：
struct protect_mem_t {
protect_mem_t( void* addr, size_t size ) : addr(addr), size(size), is_protected(FALSE) {
protect();
}
~protect_mem_t() { release(); }
BOOL protect() {
if ( !is_protected ) {
// To catch only read access you should change PAGE_NOACCESS to PAGE_READONLY
is_protected = VirtualProtect( addr, size, PAGE_NOACCESS, &old_protect );
}
return is_protected;
}
BOOL release() {
if ( is_protected )
is_protected = !VirtualProtect( addr, size, old_protect, &old_protect );
return !is_protected;
}
protected:
void* addr;
size_t size;
BOOL is_protected;
DWORD old_protect;
};
It changes access mode on selected memory pages. Page size is equal to 4096 bytes on 32-bit systems. Exception will be thrown on every access to protected memory. This class is limited in use to only large memory areas, but I hope it can be helpful.
它更改选定内存页的访问模式。页大小在 32 位系统上等于 4096 字节。每次访问受保护内存时都会抛出异常。这个类仅限于大内存区域的使用，但我希望它可以有所帮助。
It could be used in the following way:
它可以通过以下方式使用：
// some_array should be aligned on PAGE_SIZE boundaries
protect_mem_t guard( &some_array, PAGE_SIZE );
回答by steve
You can use WINDBG and set a ba breakpoint on the desired address
您可以使用 WINDBG 并在所需地址上设置 ba 断点
回答by ulatekh
I recommend the hwbreak project. It even allows a data-breakpoint to be set when a location is read.
我推荐hwbreak 项目。它甚至允许在读取位置时设置数据断点。
I modified it to only create one thread, and to reuse that thread for all data-breakpoints, but that was just for efficiency.
我修改它只创建一个线程，并为所有数据断点重用该线程，但这只是为了提高效率。
回答by MSalters
Yes, data breakpoints can detect writes. Don't know if it's possible to check for read, though. I don't believe x86 has native support for that.
是的，数据断点可以检测写入。不过，不知道是否可以检查读取。我不相信 x86 对此有本机支持。
