@@ -5,11 +5,13 @@
#ifndef AZM_AMD64_ASSEMBLER_H_
#define AZM_AMD64_ASSEMBLER_H_
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <optional>
#include <utility>
#include <variant>
#include <vector>
namespace azm::amd64 {
@@ -40,11 +42,17 @@ constexpr std::optional<std::uint8_t> register_index(Reg32 reg) {
}
struct Label {
std::size_t offset{};
};
struct Linked {
std::size_t offset{};
};
struct Unlinked {
std::vector<std::size_t> patch_offsets{};
};
struct UnlinkedLabel {
std::vector<std::size_t> patch_offsets{};
static Label linked(std::size_t jmp_target_offset) { return {Linked{jmp_target_offset}}; }
static Label unlinked() { return {Unlinked{}}; }
std::variant<Linked, Unlinked> v;
};
// https://www.felixcloutier.com/x86/
@@ -52,14 +60,16 @@ class Assembler {
public:
[[nodiscard]] std::vector<std::uint8_t> take_assembled() { return std::exchange(assembled_, {}); }
Label label() const { return Label{assembled_.size()}; }
UnlinkedLabel unlinked_label() const { return UnlinkedLabel{}; }
Label label() const { return Label::linked(assembled_.size()); }
Label unlinked_label() const { return Label::unlinked(); }
Label link(UnlinkedLabel const &label) {
void link(Label &label) {
assert(std::holds_alternative<Label::Unlinked>(label.v));
static constexpr int kInstructionSize = 4;
std::size_t const jmp_target_offset = assembled_.size();
for (std::size_t patch_offset : label.patch_offsets) {
auto const &unlinked = std::get<Label::Unlinked>(label.v);
for (std::size_t patch_offset : unlinked.patch_offsets) {
auto const rel32 = static_cast<std::uint32_t>(jmp_target_offset - patch_offset - kInstructionSize);
assembled_[patch_offset + 0] = rel32 & 0xff;
assembled_[patch_offset + 1] = (rel32 >> 8) & 0xff;
@@ -67,7 +77,7 @@ public:
assembled_[patch_offset + 3] = (rel32 >> 24) & 0xff;
}
return Label{jmp_target_offset};
label = Label::linked(jmp_target_offset);
}
// Instructions
@@ -82,17 +92,19 @@ public:
emit(imm32);
}
void jmp(Label label) {
void jmp(Label &label) {
// JMP rel32
emit(0xe9);
static constexpr int kInstructionSize = 4;
emit(Imm32{static_cast<std::uint32_t>(label.offset - assembled_.size() - kInstructionSize)});
}
if (std::holds_alternative<Label::Linked>(label.v)) {
auto const &linked = std::get<Label::Linked>(label.v);
static constexpr int kInstructionSize = 4;
emit(0xe9);
emit(Imm32{static_cast<std::uint32_t>(linked.offset - assembled_.size() - kInstructionSize)});
return;
}
void jmp(UnlinkedLabel &label) {
// JMP rel32
auto &unlinked = std::get<Label::Unlinked>(label.v);
emit(0xe9);
label.patch_offsets.push_back(assembled_.size());
unlinked.patch_offsets.push_back(assembled_.size());
emit(Imm32{0xdeadbeef});
}