Various macOS tools for mischief

Tools.cpp

#include "Tools.h"

#include <mach-o/dyld.h>
#include <mach-o/nlist.h>

#include <string_view>

namespace {

template<typename T>
auto offsetPointerTo(const void* base, ptrdiff_t offset) -> T* {
    return reinterpret_cast<T*>(ptrdiff_t(base) + offset);
}

auto findImageHeader(std::string_view imageSuffix, uint64_t& slide) -> const mach_header_64* {
    auto imageCount = _dyld_image_count();

    for (uint32_t i = 0; i < imageCount; i++) {
        auto imageName = _dyld_get_image_name(i);
        if (!imageName) {
            continue;
        }
        if (!std::string_view(imageName).ends_with(imageSuffix)) {
            continue;
        }

        slide = _dyld_get_image_vmaddr_slide(i);
        return reinterpret_cast<const mach_header_64*>(_dyld_get_image_header(i));
    }

    return nullptr;
}

auto findLINKEDIT(const mach_header_64& header) -> const segment_command_64* {
    uint64_t offset = sizeof(mach_header_64);

    for (uint32_t i = 0; i < header.ncmds; i++) {
        auto command = offsetPointerTo<const load_command>(&header, offset);

        if (command->cmd == LC_SEGMENT_64) {
            auto segment = reinterpret_cast<const segment_command_64*>(command);

            if (std::string_view(segment->segname) == SEG_LINKEDIT) {
                return segment;
            }
        }

        offset += command->cmdsize;
    }

    return nullptr;
}

auto findSYMTAB(const mach_header_64& header) -> const symtab_command* {
    uint64_t offset = sizeof(mach_header_64);

    for (uint32_t i = 0; i < header.ncmds; ++i) {
        auto command = offsetPointerTo<const load_command>(&header, offset);

        if (command->cmd == LC_SYMTAB) {
            return reinterpret_cast<const symtab_command*>(command);
        }

        offset += command->cmdsize;
    }

    return nullptr;
}

auto findSymbol(std::string_view imageSuffix, std::string_view symbol) -> void* {
    uint64_t slide = 0;

    auto header = findImageHeader(imageSuffix, slide);
    if (!header) {
        return nullptr;
    }

    auto linkedit = findLINKEDIT(*header);
    if (!linkedit) {
        return nullptr;
    }

    auto symtab = findSYMTAB(*header);
    if (!symtab) {
        return nullptr;
    }

    auto base = offsetPointerTo<void>(0, linkedit->vmaddr - linkedit->fileoff + slide);

    auto symbolTable = offsetPointerTo<const nlist_64>(base, symtab->symoff);
    auto stringTable = offsetPointerTo<const char>(base, symtab->stroff);

    for (uint32_t i = 0; i < symtab->nsyms; i++) {
        auto& nlist = symbolTable[i];
        auto name = &stringTable[nlist.n_un.n_strx];

        if (std::string_view(name) != symbol) {
            continue;
        }

        return offsetPointerTo<void*>(0, nlist.n_value + slide);
    }

    return nullptr;
}

}

void* dlsym_p(std::string_view imageSuffix, std::string_view symbol) {
    return findSymbol(imageSuffix, symbol);
}