从Swift调用getsectiondata [英] Calling getsectiondata from Swift

问题描述

此问答描述了如何在现代OS X/macOS版本上使用Objective-C从Mach-O部分读取数据:

This question and answer describe how to read data from a Mach-O section with Objective-C on modern OS X/macOS versions: Crash reading bytes from getsectbyname

所描述的答案有效.我正在尝试用Swift来实现同样的事情.我无法使其正常工作.

The described answer works. I'm trying to implement the same thing with Swift. I can't make it work.

我在其他链接器标志"中具有以下内容:-Wl,-sectcreate,__LOCALIZATIONS,__base,en.lproj/Localizable.strings,-segprot,__LOCALIZATIONS,r,r.

I have the following in "Other linker flags": -Wl,-sectcreate,__LOCALIZATIONS,__base,en.lproj/Localizable.strings,-segprot,__LOCALIZATIONS,r,r.

这个Swift代码为我提供了一个指向嵌入式数据的指针，直到我尝试在Xcode之外运行代码并且ASLR破坏了它:

This Swift code gets me the a pointer to the embedded data, until I try to run the code outside Xcode and ASLR breaks it:

var size: UInt = 0
let _localizationSection = getsectdata(
    "__LOCALIZATIONS",
    "__base",
    &size)

要解决ASLR问题，根据上述问答，并根据我自己的测试，我应该改用getsectiondata.它在Objective-C中效果很好，但是在Swift中我没有运气.以下是我设法通过编译器的唯一一件事，但它返回nil:

To get around the ASLR problem, according to the above question and answer, and based on my own testing, I should be using getsectiondata instead. It works great in Objective-C, but I'm having no luck in Swift. The following is the only thing I've managed to get past the compiler, but it returns nil:

var size: UInt = 0
var header = _mh_execute_header
let localizationSection = getsectiondata(
    &header,
    "__LOCALIZATIONS",
    "__base",
    &size)

是否正在复制_mh_execute_header问题，有什么办法可以避免它?我需要一个UnsafePointer<mach_header_64>，但是使用&_mh_execute_header作为getsectiondata的第一个参数会导致编译错误.

Is taking a copy of _mh_execute_header the problem and is there any way to avoid it? I need an UnsafePointer<mach_header_64>, but using &_mh_execute_header as the first parameter to getsectiondata causes a compilation error.

我正在使用Swift 3.0，并在macOS 10.12上运行我的代码.

I'm using Swift 3.0, and running my code on macOS 10.12.

推荐答案

链接到Objective-C代码之间的区别

The difference between the linked-to Objective-C code

void *ptr = getsectiondata(&_mh_execute_header, ...);

和您的Swift翻译

var header = _mh_execute_header
let localizationSection = getsectiondata(&header, ...)

是后者通过了全局变量的副本的地址 _mh_execute_header函数的变量，显然 不被接受.如果您将Objective-C代码修改为

is that the latter passes the address of a copy of the global _mh_execute_header variable to the function, and apparently that is not accepted. If you modify the Objective-C code to

struct mach_header_64 header = _mh_execute_header;
void *ptr = getsectiondata(&header, ...);

然后它也失败了(实际上在我的测试中崩溃了.)

then it fails as well (and actually crashed in my test).

现在的问题是_mh_execute_header暴露给Swift 作为常量:

Now the problem is that _mh_execute_header is exposed to Swift as a constant:

public let _mh_execute_header: mach_header_64

，并且不能使用Swift中的常量地址.一种可能 解决方法是定义

and one cannot take the address of a constant in Swift. One possible workaround is to define

#import <mach-o/ldsyms.h>
static const struct mach_header_64 *mhExecHeaderPtr = &_mh_execute_header;

在桥接头文件中，然后将其用作

in the bridging header file, and then use it as

let localizationSection = getsectiondata(mhExecHeaderPtr, ...)

在Swift中.

另一种选择是通过dlopen/dlsym

import MachO

if let handle = dlopen(nil, RTLD_LAZY) {
    defer { dlclose(handle) }

    if let ptr = dlsym(handle, MH_EXECUTE_SYM) {
        let mhExecHeaderPtr = ptr.assumingMemoryBound(to: mach_header_64.self)

        var size: UInt = 0
        let localizationSection = getsectiondata(
            mhExecHeaderPtr,
            "__LOCALIZATIONS",
            "__base",
            &size)

        // ...
    }
}

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