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-rw-r--r--src/codegen/x86_64.zig497
1 files changed, 497 insertions, 0 deletions
diff --git a/src/codegen/x86_64.zig b/src/codegen/x86_64.zig
index dea39f82cd..dd0b74d46a 100644
--- a/src/codegen/x86_64.zig
+++ b/src/codegen/x86_64.zig
@@ -1,4 +1,9 @@
const std = @import("std");
+const testing = std.testing;
+const mem = std.mem;
+const assert = std.debug.assert;
+const ArrayList = std.ArrayList;
+const Allocator = std.mem.Allocator;
const Type = @import("../Type.zig");
const DW = std.dwarf;
@@ -68,6 +73,11 @@ pub const Register = enum(u8) {
return @truncate(u4, @enumToInt(self));
}
+ /// Like id, but only returns the lower 3 bits.
+ pub fn low_id(self: Register) u3 {
+ return @truncate(u3, @enumToInt(self));
+ }
+
/// Returns the index into `callee_preserved_regs`.
pub fn allocIndex(self: Register) ?u4 {
return switch (self) {
@@ -136,6 +146,493 @@ pub const callee_preserved_regs = [_]Register{ .rax, .rcx, .rdx, .rsi, .rdi, .r8
pub const c_abi_int_param_regs = [_]Register{ .rdi, .rsi, .rdx, .rcx, .r8, .r9 };
pub const c_abi_int_return_regs = [_]Register{ .rax, .rdx };
+/// Encoding helper functions for x86_64 instructions
+///
+/// Many of these helpers do very little, but they can help make things
+/// slightly more readable with more descriptive field names / function names.
+///
+/// Some of them also have asserts to ensure that we aren't doing dumb things.
+/// For example, trying to use register 4 (esp) in an indirect modr/m byte is illegal,
+/// you need to encode it with an SIB byte.
+///
+/// Note that ALL of these helper functions will assume capacity,
+/// so ensure that the `code` has sufficient capacity before using them.
+/// The `init` method is the recommended way to ensure capacity.
+pub const Encoder = struct {
+ /// Non-owning reference to the code array
+ code: *ArrayList(u8),
+
+ const Self = @This();
+
+ /// Wrap `code` in Encoder to make it easier to call these helper functions
+ ///
+ /// maximum_inst_size should contain the maximum number of bytes
+ /// that the encoded instruction will take.
+ /// This is because the helper functions will assume capacity
+ /// in order to avoid bounds checking.
+ pub fn init(code: *ArrayList(u8), maximum_inst_size: u8) !Self {
+ try code.ensureCapacity(code.items.len + maximum_inst_size);
+ return Self{ .code = code };
+ }
+
+ /// Directly write a number to the code array with big endianness
+ pub fn writeIntBig(self: Self, comptime T: type, value: T) void {
+ mem.writeIntBig(
+ T,
+ self.code.addManyAsArrayAssumeCapacity(@divExact(@typeInfo(T).Int.bits, 8)),
+ value,
+ );
+ }
+
+ /// Directly write a number to the code array with little endianness
+ pub fn writeIntLittle(self: Self, comptime T: type, value: T) void {
+ mem.writeIntLittle(
+ T,
+ self.code.addManyAsArrayAssumeCapacity(@divExact(@typeInfo(T).Int.bits, 8)),
+ value,
+ );
+ }
+
+ // --------
+ // Prefixes
+ // --------
+
+ pub const LegacyPrefixes = packed struct {
+ /// LOCK
+ prefix_f0: bool = false,
+ /// REPNZ, REPNE, REP, Scalar Double-precision
+ prefix_f2: bool = false,
+ /// REPZ, REPE, REP, Scalar Single-precision
+ prefix_f3: bool = false,
+
+ /// CS segment override or Branch not taken
+ prefix_2e: bool = false,
+ /// DS segment override
+ prefix_36: bool = false,
+ /// ES segment override
+ prefix_26: bool = false,
+ /// FS segment override
+ prefix_64: bool = false,
+ /// GS segment override
+ prefix_65: bool = false,
+
+ /// Branch taken
+ prefix_3e: bool = false,
+
+ /// Operand size override (enables 16 bit operation)
+ prefix_66: bool = false,
+
+ /// Address size override (enables 16 bit address size)
+ prefix_67: bool = false,
+
+ padding: u5 = 0,
+ };
+
+ /// Encodes legacy prefixes
+ pub fn legacyPrefixes(self: Self, prefixes: LegacyPrefixes) void {
+ if (@bitCast(u16, prefixes) != 0) {
+ // Hopefully this path isn't taken very often, so we'll do it the slow way for now
+
+ // LOCK
+ if (prefixes.prefix_f0) self.code.appendAssumeCapacity(0xf0);
+ // REPNZ, REPNE, REP, Scalar Double-precision
+ if (prefixes.prefix_f2) self.code.appendAssumeCapacity(0xf2);
+ // REPZ, REPE, REP, Scalar Single-precision
+ if (prefixes.prefix_f3) self.code.appendAssumeCapacity(0xf3);
+
+ // CS segment override or Branch not taken
+ if (prefixes.prefix_2e) self.code.appendAssumeCapacity(0x2e);
+ // DS segment override
+ if (prefixes.prefix_36) self.code.appendAssumeCapacity(0x36);
+ // ES segment override
+ if (prefixes.prefix_26) self.code.appendAssumeCapacity(0x26);
+ // FS segment override
+ if (prefixes.prefix_64) self.code.appendAssumeCapacity(0x64);
+ // GS segment override
+ if (prefixes.prefix_65) self.code.appendAssumeCapacity(0x65);
+
+ // Branch taken
+ if (prefixes.prefix_3e) self.code.appendAssumeCapacity(0x3e);
+
+ // Operand size override
+ if (prefixes.prefix_66) self.code.appendAssumeCapacity(0x66);
+
+ // Address size override
+ if (prefixes.prefix_67) self.code.appendAssumeCapacity(0x67);
+ }
+ }
+
+ /// Use 16 bit operand size
+ ///
+ /// Note that this flag is overridden by REX.W, if both are present.
+ pub fn prefix16BitMode(self: Self) void {
+ self.code.appendAssumeCapacity(0x66);
+ }
+
+ /// From section 2.2.1.2 of the manual, REX is encoded as b0100WRXB
+ pub const Rex = struct {
+ /// Wide, enables 64-bit operation
+ w: bool = false,
+ /// Extends the reg field in the ModR/M byte
+ r: bool = false,
+ /// Extends the index field in the SIB byte
+ x: bool = false,
+ /// Extends the r/m field in the ModR/M byte,
+ /// or the base field in the SIB byte,
+ /// or the reg field in the Opcode byte
+ b: bool = false,
+ };
+
+ /// Encodes a REX prefix byte given all the fields
+ ///
+ /// Use this byte whenever you need 64 bit operation,
+ /// or one of reg, index, r/m, base, or opcode-reg might be extended.
+ ///
+ /// See struct `Rex` for a description of each field.
+ ///
+ /// Does not add a prefix byte if none of the fields are set!
+ pub fn rex(self: Self, byte: Rex) void {
+ var value: u8 = 0b0100_0000;
+
+ if (byte.w) value |= 0b1000;
+ if (byte.r) value |= 0b0100;
+ if (byte.x) value |= 0b0010;
+ if (byte.b) value |= 0b0001;
+
+ if (value != 0b0100_0000) {
+ self.code.appendAssumeCapacity(value);
+ }
+ }
+
+ // ------
+ // Opcode
+ // ------
+
+ /// Encodes a 1 byte opcode
+ pub fn opcode_1byte(self: Self, opcode: u8) void {
+ self.code.appendAssumeCapacity(opcode);
+ }
+
+ /// Encodes a 2 byte opcode
+ ///
+ /// e.g. IMUL has the opcode 0x0f 0xaf, so you use
+ ///
+ /// encoder.opcode_2byte(0x0f, 0xaf);
+ pub fn opcode_2byte(self: Self, prefix: u8, opcode: u8) void {
+ self.code.appendAssumeCapacity(prefix);
+ self.code.appendAssumeCapacity(opcode);
+ }
+
+ /// Encodes a 1 byte opcode with a reg field
+ ///
+ /// Remember to add a REX prefix byte if reg is extended!
+ pub fn opcode_withReg(self: Self, opcode: u8, reg: u3) void {
+ assert(opcode & 0b111 == 0);
+ self.code.appendAssumeCapacity(opcode | reg);
+ }
+
+ // ------
+ // ModR/M
+ // ------
+
+ /// Construct a ModR/M byte given all the fields
+ ///
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm(self: Self, mod: u2, reg_or_opx: u3, rm: u3) void {
+ self.code.appendAssumeCapacity(
+ @as(u8, mod) << 6 | @as(u8, reg_or_opx) << 3 | rm,
+ );
+ }
+
+ /// Construct a ModR/M byte using direct r/m addressing
+ /// r/m effective address: r/m
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_direct(self: Self, reg_or_opx: u3, rm: u3) void {
+ self.modRm(0b11, reg_or_opx, rm);
+ }
+
+ /// Construct a ModR/M byte using indirect r/m addressing
+ /// r/m effective address: [r/m]
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_indirectDisp0(self: Self, reg_or_opx: u3, rm: u3) void {
+ assert(rm != 4 and rm != 5);
+ self.modRm(0b00, reg_or_opx, rm);
+ }
+
+ /// Construct a ModR/M byte using indirect SIB addressing
+ /// r/m effective address: [SIB]
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_SIBDisp0(self: Self, reg_or_opx: u3) void {
+ self.modRm(0b00, reg_or_opx, 0b100);
+ }
+
+ /// Construct a ModR/M byte using RIP-relative addressing
+ /// r/m effective address: [RIP + disp32]
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_RIPDisp32(self: Self, reg_or_opx: u3) void {
+ self.modRm(0b00, reg_or_opx, 0b101);
+ }
+
+ /// Construct a ModR/M byte using indirect r/m with a 8bit displacement
+ /// r/m effective address: [r/m + disp8]
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_indirectDisp8(self: Self, reg_or_opx: u3, rm: u3) void {
+ assert(rm != 4);
+ self.modRm(0b01, reg_or_opx, rm);
+ }
+
+ /// Construct a ModR/M byte using indirect SIB with a 8bit displacement
+ /// r/m effective address: [SIB + disp8]
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_SIBDisp8(self: Self, reg_or_opx: u3) void {
+ self.modRm(0b01, reg_or_opx, 0b100);
+ }
+
+ /// Construct a ModR/M byte using indirect r/m with a 32bit displacement
+ /// r/m effective address: [r/m + disp32]
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_indirectDisp32(self: Self, reg_or_opx: u3, rm: u3) void {
+ assert(rm != 4);
+ self.modRm(0b10, reg_or_opx, rm);
+ }
+
+ /// Construct a ModR/M byte using indirect SIB with a 32bit displacement
+ /// r/m effective address: [SIB + disp32]
+ ///
+ /// Note reg's effective address is always just reg for the ModR/M byte.
+ /// Remember to add a REX prefix byte if reg or rm are extended!
+ pub fn modRm_SIBDisp32(self: Self, reg_or_opx: u3) void {
+ self.modRm(0b10, reg_or_opx, 0b100);
+ }
+
+ // ---
+ // SIB
+ // ---
+
+ /// Construct a SIB byte given all the fields
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib(self: Self, scale: u2, index: u3, base: u3) void {
+ self.code.appendAssumeCapacity(
+ @as(u8, scale) << 6 | @as(u8, index) << 3 | base,
+ );
+ }
+
+ /// Construct a SIB byte with scale * index + base, no frills.
+ /// r/m effective address: [base + scale * index]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_scaleIndexBase(self: Self, scale: u2, index: u3, base: u3) void {
+ assert(base != 5);
+
+ self.sib(scale, index, base);
+ }
+
+ /// Construct a SIB byte with scale * index + disp32
+ /// r/m effective address: [scale * index + disp32]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_scaleIndexDisp32(self: Self, scale: u2, index: u3) void {
+ assert(index != 4);
+
+ // scale is actually ignored
+ // index = 4 means no index
+ // base = 5 means no base, if mod == 0.
+ self.sib(scale, index, 5);
+ }
+
+ /// Construct a SIB byte with just base
+ /// r/m effective address: [base]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_base(self: Self, base: u3) void {
+ assert(base != 5);
+
+ // scale is actually ignored
+ // index = 4 means no index
+ self.sib(0, 4, base);
+ }
+
+ /// Construct a SIB byte with just disp32
+ /// r/m effective address: [disp32]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_disp32(self: Self) void {
+ // scale is actually ignored
+ // index = 4 means no index
+ // base = 5 means no base, if mod == 0.
+ self.sib(0, 4, 5);
+ }
+
+ /// Construct a SIB byte with scale * index + base + disp8
+ /// r/m effective address: [base + scale * index + disp8]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_scaleIndexBaseDisp8(self: Self, scale: u2, index: u3, base: u3) void {
+ self.sib(scale, index, base);
+ }
+
+ /// Construct a SIB byte with base + disp8, no index
+ /// r/m effective address: [base + disp8]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_baseDisp8(self: Self, base: u3) void {
+ // scale is ignored
+ // index = 4 means no index
+ self.sib(0, 4, base);
+ }
+
+ /// Construct a SIB byte with scale * index + base + disp32
+ /// r/m effective address: [base + scale * index + disp32]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_scaleIndexBaseDisp32(self: Self, scale: u2, index: u3, base: u3) void {
+ self.sib(scale, index, base);
+ }
+
+ /// Construct a SIB byte with base + disp32, no index
+ /// r/m effective address: [base + disp32]
+ ///
+ /// Remember to add a REX prefix byte if index or base are extended!
+ pub fn sib_baseDisp32(self: Self, base: u3) void {
+ // scale is ignored
+ // index = 4 means no index
+ self.sib(0, 4, base);
+ }
+
+ // -------------------------
+ // Trivial (no bit fiddling)
+ // -------------------------
+
+ /// Encode an 8 bit immediate
+ ///
+ /// It is sign-extended to 64 bits by the cpu.
+ pub fn imm8(self: Self, imm: i8) void {
+ self.code.appendAssumeCapacity(@bitCast(u8, imm));
+ }
+
+ /// Encode an 8 bit displacement
+ ///
+ /// It is sign-extended to 64 bits by the cpu.
+ pub fn disp8(self: Self, disp: i8) void {
+ self.code.appendAssumeCapacity(@bitCast(u8, disp));
+ }
+
+ /// Encode an 16 bit immediate
+ ///
+ /// It is sign-extended to 64 bits by the cpu.
+ pub fn imm16(self: Self, imm: i16) void {
+ self.writeIntLittle(i16, imm);
+ }
+
+ /// Encode an 32 bit immediate
+ ///
+ /// It is sign-extended to 64 bits by the cpu.
+ pub fn imm32(self: Self, imm: i32) void {
+ self.writeIntLittle(i32, imm);
+ }
+
+ /// Encode an 32 bit displacement
+ ///
+ /// It is sign-extended to 64 bits by the cpu.
+ pub fn disp32(self: Self, disp: i32) void {
+ self.writeIntLittle(i32, disp);
+ }
+
+ /// Encode an 64 bit immediate
+ ///
+ /// It is sign-extended to 64 bits by the cpu.
+ pub fn imm64(self: Self, imm: u64) void {
+ self.writeIntLittle(u64, imm);
+ }
+};
+
+test "x86_64 Encoder helpers" {
+ var code = ArrayList(u8).init(testing.allocator);
+ defer code.deinit();
+
+ // simple integer multiplication
+
+ // imul eax,edi
+ // 0faf c7
+ {
+ try code.resize(0);
+ const encoder = try Encoder.init(&code, 4);
+ encoder.rex(.{
+ .r = Register.eax.isExtended(),
+ .b = Register.edi.isExtended(),
+ });
+ encoder.opcode_2byte(0x0f, 0xaf);
+ encoder.modRm_direct(
+ Register.eax.low_id(),
+ Register.edi.low_id(),
+ );
+
+ testing.expectEqualSlices(u8, &[_]u8{ 0x0f, 0xaf, 0xc7 }, code.items);
+ }
+
+ // simple mov
+
+ // mov eax,edi
+ // 89 f8
+ {
+ try code.resize(0);
+ const encoder = try Encoder.init(&code, 3);
+ encoder.rex(.{
+ .r = Register.edi.isExtended(),
+ .b = Register.eax.isExtended(),
+ });
+ encoder.opcode_1byte(0x89);
+ encoder.modRm_direct(
+ Register.edi.low_id(),
+ Register.eax.low_id(),
+ );
+
+ testing.expectEqualSlices(u8, &[_]u8{ 0x89, 0xf8 }, code.items);
+ }
+
+ // signed integer addition of 32-bit sign extended immediate to 64 bit register
+
+ // add rcx, 2147483647
+ //
+ // Using the following opcode: REX.W + 81 /0 id, we expect the following encoding
+ //
+ // 48 : REX.W set for 64 bit operand (*r*cx)
+ // 81 : opcode for "<arithmetic> with immediate"
+ // c1 : id = rcx,
+ // : c1 = 11 <-- mod = 11 indicates r/m is register (rcx)
+ // : 000 <-- opcode_extension = 0 because opcode extension is /0. /0 specifies ADD
+ // : 001 <-- 001 is rcx
+ // ffffff7f : 2147483647
+ {
+ try code.resize(0);
+ const encoder = try Encoder.init(&code, 7);
+ encoder.rex(.{ .w = true }); // use 64 bit operation
+ encoder.opcode_1byte(0x81);
+ encoder.modRm_direct(
+ 0,
+ Register.rcx.low_id(),
+ );
+ encoder.imm32(2147483647);
+
+ testing.expectEqualSlices(u8, &[_]u8{ 0x48, 0x81, 0xc1, 0xff, 0xff, 0xff, 0x7f }, code.items);
+ }
+}
+
// TODO add these registers to the enum and populate dwarfLocOp
// // Return Address register. This is stored in `0(%rsp, "")` and is not a physical register.
// RA = (16, "RA"),
generated by cgit v1.2.3 (git 2.39.1) at 2025-12-28 16:39:03 +0000