jcc_rewrite_pass.cpp

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// Copyright (c) 2022, _xeroxz
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// 1. Redistributions of source code must retain the above copyright notice,
//    this list of conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
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#include <obf/passes/jcc_rewrite_pass.hpp>
#include <obf/passes/next_inst_pass.hpp>
 
namespace theo::obf {
jcc_rewrite_pass_t* jcc_rewrite_pass_t::get() {
  static jcc_rewrite_pass_t obj;
  return &obj;
}
 
void jcc_rewrite_pass_t::run(decomp::symbol_t* sym) {
  std::int32_t disp = {};
  xed_decoded_inst_t inst;
  xed_state_t istate{XED_MACHINE_MODE_LONG_64, XED_ADDRESS_WIDTH_64b};
  xed_decoded_inst_zero_set_mode(&inst, &istate);
  xed_decode(&inst, sym->data().data(), XED_MAX_INSTRUCTION_BYTES);
 
  // if the instruction is branching...
  if ((disp = xed_decoded_inst_get_branch_displacement(&inst))) {
    disp += xed_decoded_inst_get_length(&inst);
 
    // update displacement...
    xed_decoded_inst_set_branch_displacement(
        &inst, sym->data().size() - xed_decoded_inst_get_length(&inst),
        xed_decoded_inst_get_branch_displacement_width(&inst));
 
    xed_encoder_request_init_from_decode(&inst);
    xed_encoder_request_t* req = &inst;
 
    // update jcc in the buffer...
    std::uint32_t len = {};
    xed_encode(req, sym->data().data(), xed_decoded_inst_get_length(&inst),
               &len);
 
    // create a relocation to the instruction the branch would normally go
    // too...
    auto offset = disp < 0 ? sym->offset() - std::abs(disp)
                           : sym->offset() + std::abs(disp);
 
    auto sym_name =
        std::string(
            sym->sym()->name.to_string(sym->img()->get_strings()).data())
            .append("@")
            .append(std::to_string(offset));
 
    sym->relocs().push_back(
        recomp::reloc_t(0, decomp::symbol_t::hash(sym_name), sym_name.data()));
 
    // run next_inst_pass on this symbol to generate the transformations for the
    // relocation to the jcc branch dest instruction...
    next_inst_pass_t::get()->run(sym);
  }
};
}  // namespace theo::obf