更换功能单元 [英] Replace function units

问题描述

我正在为大型Delphi代码库编写单元测试基础设施。我想将SysUtils.FileExists中的纯函数的调用链接到MockSysUtils.FileExists。

创建具有相同接口的SysUtils单元不被欣赏通过编译器。

我在想的是在运行时挂钩我的模拟功能。这是可能现在吗？

其他任何建议？

请问，

Peter

解决方案

在运行时更换功能很困难，但通常在技术上是可能的。 所有您需要做的是：

• 拿出有问题的功能的地址


• 拆卸前5个字节（以检查RET指令 - 非常小的例程可能会与另一个例程相抵触，阻止您更换）


• 更改其页面保护（使用 VirtualProtect ）可写入


• 使用JMP rel32指令重写前5个字节（即E9 ）


• 实现您的版本功能正常，确保它具有与您嘲笑的功能相同的参数和调用约定

更简单的方法要链接到不同版本的SysUtils.pas。这将需要您重新编译依赖于SysUtils.pas的RTL和VCL中的所有单元，但它可能比上述功能文件格式更容易。

最简单的方法是语言级别，您不必直接依赖于SysUtils（因此可以在较高级别切换），或者您修改使用声明有条件地引用不同的单位。

I am writing a unit test infrastructure for a large Delphi code base. I would like to link calls to pure functions in SysUtils.FileExists for example to a "MockSysUtils.FileExists" instead.

Creating a SysUtils unit with the same interface is not appreciated by the compiler.

What I am thinking of is to hook in my mock function at runtime. Is this possible nowadays?

Any other suggestions?

Regards,

Peter

解决方案

Replacing a function at runtime is difficult but usually technically possible. "All" you need to do is:

• take the address of the function in question
• disassemble the first 5 bytes or so (to check for a RET instruction - very small routines may abut another routine, preventing you from replacing it)
• change its page protection (with VirtualProtect) to be writable
• rewrite the first 5 bytes with a JMP rel32 instruction (i.e. E9 <offset-to-your-func>)
• implement your version function as normal, making sure it has the same arguments and calling convention as the function you are mocking

An easier approach would be to link against a different version of SysUtils.pas. That will require you to also recompile all the units in the RTL and VCL that depend on SysUtils.pas, but it is likely quite a bit easier than the function intrumentation approach described above.

The easiest approach is the language-level one, where either you don't directly rely on SysUtils at all (and so can switch at a higher level), or you modify the uses declaration to conditionally refer to a different unit.

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