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Eliminate length extension.

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This commit is contained in:
Thomas Harte 2023-10-26 23:19:31 -04:00
parent 8e35a56ff7
commit 11b032fb06
4 changed files with 31 additions and 58 deletions
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2
InstructionSets/x86/Implementation/PerformImplementation.hpp
View File

@ -1636,7 +1636,7 @@ template <
// * use hard-coded register names where appropriate;
// * return directly if there is definitely no possible write back to RAM;
// * otherwise use the source() and destination() lambdas, and break in order to allow a writeback if necessary.
switch(instruction.operation) {
switch(instruction.operation()) {
default:
assert(false);

12
InstructionSets/x86/Instruction.cpp
View File

@ -420,7 +420,7 @@ std::string InstructionSet::x86::to_string(
case Source::IndirectNoBase: {
std::stringstream stream;
if(!InstructionSet::x86::mnemonic_implies_data_size(instruction.operation)) {
if(!InstructionSet::x86::mnemonic_implies_data_size(instruction.operation())) {
stream << InstructionSet::x86::to_string(operation_size) << ' ';
}
@ -473,7 +473,7 @@ std::string InstructionSet::x86::to_string(
std::string operation;
// Add segment override, if any, ahead of some operations that won't otherwise print it.
switch(instruction.second.operation) {
switch(instruction.second.operation()) {
default: break;
case Operation::CMPS:
@ -505,14 +505,14 @@ std::string InstructionSet::x86::to_string(
}
// Add operation itself.
operation += to_string(instruction.second.operation, instruction.second.operation_size(), model);
operation += to_string(instruction.second.operation(), instruction.second.operation_size(), model);
operation += " ";
// Deal with a few special cases up front.
switch(instruction.second.operation) {
switch(instruction.second.operation()) {
default: {
const int operands = max_displayed_operands(instruction.second.operation);
const bool displacement = has_displacement(instruction.second.operation);
const int operands = max_displayed_operands(instruction.second.operation());
const bool displacement = has_displacement(instruction.second.operation());
const bool print_first = operands > 1 && instruction.second.destination().source() != Source::None;
if(print_first) {
operation += to_string(instruction.second.destination(), instruction.second, offset_length, immediate_length);

67
InstructionSets/x86/Instruction.hpp
View File

@ -662,10 +662,12 @@ class DataPointer {
template<bool is_32bit> class Instruction {
public:
Operation operation = Operation::Invalid;
Operation operation() const {
return operation_;
}
bool operator ==(const Instruction<is_32bit> &rhs) const {
if( operation != rhs.operation ||
if( operation_ != rhs.operation_ ||
mem_exts_source_ != rhs.mem_exts_source_ ||
source_data_dest_sib_ != rhs.source_data_dest_sib_) {
return false;
@ -673,7 +675,7 @@ template<bool is_32bit> class Instruction {
// Have already established above that this and RHS have the
// same extensions, if any.
const int extension_count = has_length_extension() + has_displacement() + has_operand();
const int extension_count = has_displacement() + has_operand();
for(int c = 0; c < extension_count; c++) {
if(extensions_[c] != rhs.extensions_[c]) return false;
}
@ -686,6 +688,8 @@ template<bool is_32bit> class Instruction {
using AddressT = ImmediateT;
private:
Operation operation_ = Operation::Invalid;
// Packing and encoding of fields is admittedly somewhat convoluted; what this
// achieves is that instructions will be sized:
//
@ -711,34 +715,14 @@ template<bool is_32bit> class Instruction {
}
// [b15, b14]: data size;
// [b13, b10]: source length (0 => has length extension);
// [b13]: lock;
// [b12, b10]: segment override;
// [b9, b5]: top five of SIB;
// [b4, b0]: dest.
uint16_t source_data_dest_sib_ = 1 << 10; // So that ::Invalid doesn't seem to have a length extension.
uint16_t source_data_dest_sib_ = 0;
// Note to future self: if source length continues to prove avoidable, reuse its four bits as:
// three bits: segment (as overridden, otherwise whichever operand has a segment, if either);
// one bit: an extra bit for Operation.
//
// Then what was the length extension will hold only a repetition, if any, and the lock bit. As luck would have
// it there are six valid segment registers so there is an available sentinel value to put into the segment
// field to indicate that there's an extension if necessary. A further three bits would need to be trimmed
// to do away with that extension entirely, but since lock is rarely used and repetitions apply only to a
// small number of operations I think it'd at least be a limited problem.
bool has_length_extension() const {
return !((source_data_dest_sib_ >> 10) & 15);
}
// {operand}, {displacement}, {length extension}.
//
// If length extension is present then:
//
// [b15, b6]: source length;
// [b5, b4]: repetition;
// [b3, b1]: segment override;
// b0: lock.
ImmediateT extensions_[3]{};
// {operand}, {displacement}.
ImmediateT extensions_[2]{};
ImmediateT operand_extension() const {
return extensions_[0];
@ -746,9 +730,6 @@ template<bool is_32bit> class Instruction {
ImmediateT displacement_extension() const {
return extensions_[(mem_exts_source_ >> 5) & 1];
}
ImmediateT length_extension() const {
return extensions_[((mem_exts_source_ >> 5) & 1) + ((mem_exts_source_ >> 6) & 1)];
}
public:
/// @returns The number of bytes used for meaningful content within this class. A receiver must use at least @c sizeof(Instruction) bytes
@ -757,7 +738,7 @@ template<bool is_32bit> class Instruction {
size_t packing_size() const {
return
offsetof(Instruction<is_32bit>, extensions) +
(has_displacement() + has_operand() + has_length_extension()) * sizeof(ImmediateT);
(has_displacement() + has_operand()) * sizeof(ImmediateT);
// To consider in the future: the length extension is always the last one,
// and uses only 8 bits of content within 32-bit instructions, so it'd be
@ -788,7 +769,7 @@ template<bool is_32bit> class Instruction {
);
}
bool lock() const {
return has_length_extension() && length_extension()&1;
return source_data_dest_sib_ & (1 << 13);
}
AddressSize address_size() const {
@ -800,10 +781,9 @@ template<bool is_32bit> class Instruction {
/// or that used by stack instructions, but this function does not spend the time necessary to provide
/// the correct default for those.
Source segment_override() const {
if(!has_length_extension()) return Source::None;
return Source(
int(Source::ES) +
((length_extension() >> 1) & 7)
((source_data_dest_sib_ >> 10) & 7)
);
}
@ -844,7 +824,7 @@ template<bool is_32bit> class Instruction {
DataSize data_size,
DisplacementT displacement,
ImmediateT operand) noexcept :
operation(operation),
operation_(operation),
mem_exts_source_(uint8_t(
(int(address_size) << 7) |
(displacement ? 0x40 : 0x00) |
@ -854,14 +834,13 @@ template<bool is_32bit> class Instruction {
)),
source_data_dest_sib_(uint16_t(
(int(data_size) << 14) |
((
(lock || (segment_override != Source::None))
) ? 0 : (1 << 10)) |
(lock ? (1 << 13) : 0) |
((int(segment_override)&7) << 10) |
((uint8_t(sib) & 0xf8) << 2) |
int(destination) |
(destination == Source::Indirect ? (uint8_t(sib) & 7) : 0)
)) {
))
{
// Decisions on whether to include operand, displacement and/or size extension words
// have implicitly been made in the int packing above; honour them here.
int extension = 0;
@ -873,12 +852,6 @@ template<bool is_32bit> class Instruction {
extensions_[extension] = ImmediateT(displacement);
++extension;
}
if(has_length_extension()) {
extensions_[extension] = ImmediateT(
((int(segment_override) & 7) << 1) | int(lock)
);
++extension;
}
}
};

8
OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm
View File

@ -21,7 +21,7 @@ namespace {
template <typename InstructionT> void test(const InstructionT &instruction, DataSize size, Operation operation) {
XCTAssertEqual(instruction.operation_size(), InstructionSet::x86::DataSize(size));
XCTAssertEqual(instruction.operation, operation);
XCTAssertEqual(instruction.operation(), operation);
}
template <typename InstructionT> void test(
@ -34,7 +34,7 @@ template <typename InstructionT> void test(
std::optional<typename InstructionT::DisplacementT> displacement = std::nullopt) {
XCTAssertEqual(instruction.operation_size(), InstructionSet::x86::DataSize(size));
XCTAssertEqual(instruction.operation, operation);
XCTAssertEqual(instruction.operation(), operation);
if(source) XCTAssert(instruction.source() == *source);
if(destination) XCTAssert(instruction.destination() == *destination);
if(operand) XCTAssertEqual(instruction.operand(), *operand);
@ -46,7 +46,7 @@ template <typename InstructionT> void test(
Operation operation,
std::optional<typename InstructionT::ImmediateT> operand = std::nullopt,
std::optional<typename InstructionT::DisplacementT> displacement = std::nullopt) {
XCTAssertEqual(instruction.operation, operation);
XCTAssertEqual(instruction.operation(), operation);
if(operand) XCTAssertEqual(instruction.operand(), *operand);
if(displacement) XCTAssertEqual(instruction.displacement(), *displacement);
}
@ -56,7 +56,7 @@ template <typename InstructionT> void test_far(
Operation operation,
uint16_t segment,
typename InstructionT::DisplacementT offset) {
XCTAssertEqual(instruction.operation, operation);
XCTAssertEqual(instruction.operation(), operation);
XCTAssertEqual(instruction.segment(), segment);
XCTAssertEqual(instruction.offset(), offset);
}