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Resolve default segment question.

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This commit is contained in:
Thomas Harte 2022-03-10 20:27:35 -05:00
parent bf7faa80c1
commit 641e0c1afc
1 changed files with 9 additions and 19 deletions
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28
InstructionSets/x86/Instruction.hpp
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@ -434,23 +434,6 @@ enum class Source: uint8_t {
IndirectNoBase = Indirect - 1,
};
constexpr Source default_data_segment([[maybe_unused]] Operation operation) {
// TODO: is this really necessary, or can ::DS always be default?
// i.e. can the stack operations actually take a segment override?
// If not then the actual implementations just won't ask about a segment.
// constexpr std::set<Operation> stack_ops = {
//
// };
//
// if(
// operation == Operation::PUSH ||
// operation == Operation::PUSHF ||
// operation == Operation::POP) {
// return Source::SS;
// }
return Source::DS;
}
enum class Repetition: uint8_t {
None, RepE, RepNE
};
@ -696,8 +679,13 @@ template<bool is_32bit> class Instruction {
AddressSize address_size() const {
return AddressSize(mem_exts_source_ >> 7);
}
/// @returns @c Source::DS if no segment override was found; the overridden segment otherwise.
/// On x86 a segment override cannot modify the segment used as a destination in string instructions,
/// or that used by stack instructions, but this function does not spend the time necessary to provide
/// the correct default for those.
Source data_segment() const {
if(!has_length_extension()) return default_data_segment(operation);
if(!has_length_extension()) return Source::DS;
return Source(
int(Source::ES) +
((extensions_[0] >> 1) & 7)
@ -768,7 +756,9 @@ template<bool is_32bit> class Instruction {
int extension = 0;
if(has_length_extension()) {
if(segment_override == Source::None) segment_override = default_data_segment(operation);
// As per the rule stated for segment(), this class provides ::DS for any instruction
// that doesn't have a segment override.
if(segment_override == Source::None) segment_override = Source::DS;
extensions_[extension] = ImmediateT(
(length << 6) | (int(repetition) << 4) | ((int(segment_override) & 7) << 1) | int(lock)
);