dyld-shared-cache-big-sur

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Per discussion in #2 here are the changes I've made. I don't know if its useful or not, but feel free to disregard if it isn't. I think it should fix up the objective-c things you were already doing, but should more generically fix up pointers found in __DATA as well as symbols.

Here are some notes:

• My c++ is terrible; I'm really sorry
• This is an adaptation of the work done in https://github.com/zhuowei/dsc_extractor_badly
• The important, but not obvious parts are changes made to structures in launch-cache/dyld_cache_format.h, especially location of undocumented mapping structs that point to slide info structs
• There is a bunch of stuff that this doesn't do correctly, including:
  • There are broken references from __TEXT to __DATA
  • Some libraries, such as libswiftSceneKit are almost complete nonsense
• It would be worth looking at the objective-c stuff in dsc_extractor_badly, as I didn't integrate that. The specific library I cared about wasn't obj-c

Let me know if I can help or if there are things here I can help explain

Thank you! Excited to finally take a look at this.

This will segfault while parsing libraries with no __DATA section, of which there are a few.

A fix:

//dsc_extractor.cpp

-- auto ret = slideOneSegment(dataSeg, 1, saved_vmaddrs[1], section_adjustments);

++ const macho_segment_command<P> *dataSeg = mh->getSegment("__DATA");
++ if(!dataSeg) {
++    return static_cast<std::vector<uint8_t>>(NULL);
++ }
++ auto ret = slideOneSegment(dataSeg, 1, saved_vmaddrs[1], section_adjustments);