feat(v5te): implement THUMB BLX(1), BLX(2), and ARM BLX

src/arm.zig

@@ -371,7 +371,7 @@ pub fn Arm32(comptime isa: Architecture) type {
 
                 if (self.cpsr.check(Self.arch, cond)) {
                     if (isa == .v5te and cond == 0b1111) {
-                        self.panic("TODO: Unconditional Instruction Extension Space\nopcode: 0x{X:0>8} | idx: 0x{X:} | ptr: {any}", .{ opcode, arm.idx(opcode), arm.lut[arm.idx(opcode)] });
+                        std.log.debug("TODO: Unconditional Instruction Extension Space\nopcode: 0x{X:0>8} | idx: 0x{X:} | ptr: {any}", .{ opcode, arm.idx(opcode), arm.lut[arm.idx(opcode)] });
                     }
 
                     arm.lut[arm.idx(opcode)](self, opcode);

src/arm/cpu/arm/branch.zig

@@ -5,9 +5,24 @@ pub fn branch(comptime InstrFn: type, comptime L: bool) InstrFn {
 
     return struct {
         fn inner(cpu: *Arm32, opcode: u32) void {
+            const cond: u4 = @truncate(opcode >> 28);
+            switch (cond) {
+                0b1111 => { // BLX
+                    const H = L;
+                    const offset = sext(u32, u24, opcode) << 2 | @as(u32, @intFromBool(H)) << 1;
+
+                    cpu.r[14] = cpu.r[15] - 4;
+                    cpu.cpsr.t.set();
+
+                    cpu.r[15] +%= offset;
+                },
+                else => {
                     if (L) cpu.r[14] = cpu.r[15] - 4;
 
                     cpu.r[15] +%= sext(u32, u24, opcode) << 2;
+                },
+            }
+
             cpu.pipe.reload(cpu);
         }
     }.inner;

src/arm/cpu/thumb/branch.zig

@@ -17,38 +17,37 @@ pub fn fmt16(comptime InstrFn: type, comptime cond: u4) InstrFn {
     }.inner;
 }
 
-pub fn fmt18(comptime InstrFn: type) InstrFn {
+pub fn linkExchange(comptime InstrFn: type, comptime H: u2) InstrFn {
-    const Arm32 = @typeInfo(@typeInfo(@typeInfo(InstrFn).Pointer.child).Fn.params[0].type.?).Pointer.child;
-
-    return struct {
-        // B but conditional
-        fn inner(cpu: *Arm32, opcode: u16) void {
-            cpu.r[15] +%= sext(u32, u11, opcode & 0x7FF) << 1;
-            cpu.pipe.reload(cpu);
-        }
-    }.inner;
-}
-
-pub fn fmt19(comptime InstrFn: type, comptime is_low: bool) InstrFn {
     const Arm32 = @typeInfo(@typeInfo(@typeInfo(InstrFn).Pointer.child).Fn.params[0].type.?).Pointer.child;
 
     return struct {
         fn inner(cpu: *Arm32, opcode: u16) void {
-            // BL
             const offset = opcode & 0x7FF;
 
-            if (is_low) {
+            switch (H) {
-                // Instruction 2
+                0b00 => { // Unconditional Branch
-                const next_opcode = cpu.r[15] - 2;
+                    cpu.r[15] +%= sext(u32, u11, opcode & 0x7FF) << 1;
+                    cpu.pipe.reload(cpu);
+                },
+                0b01 => { // BLX Pt. 2
+                    if (Arm32.arch == .v4t) cpu.panic("attempted to execute THUMB BLX(1), despite ARMv4T CPU", .{});
+                    const next_addr = cpu.r[15] - 2;
 
-                cpu.r[15] = cpu.r[14] +% (offset << 1);
+                    cpu.r[15] = (cpu.r[14] +% (offset << 1)) & ~@as(u32, 0x3);
-                cpu.r[14] = next_opcode | 1;
+                    cpu.r[14] = next_addr | 1;
+                    cpu.cpsr.t.unset();
 
                     cpu.pipe.reload(cpu);
-            } else {
+                },
-                // Instruction 1
+                0b10 => cpu.r[14] = cpu.r[15] +% (sext(u32, u11, offset) << 12), // BL / BLX Pt. 1
-                const lr_offset = sext(u32, u11, offset) << 12;
+                0b11 => { // BL Pt. 2
-                cpu.r[14] = (cpu.r[15] +% lr_offset) & ~@as(u32, 1);
+                    const next_addr = cpu.r[15] - 2;
+
+                    cpu.r[15] = cpu.r[14] +% (offset << 1);
+                    cpu.r[14] = next_addr | 1;
+
+                    cpu.pipe.reload(cpu);
+                },
             }
         }
     }.inner;

src/arm/cpu/thumb/data_processing.zig

@@ -60,6 +60,17 @@ pub fn fmt5(comptime InstrFn: type, comptime op: u2, comptime h1: u1, comptime h
             const rs = @as(u4, h2) << 3 | (opcode >> 3 & 0x7);
             const rd = @as(u4, h1) << 3 | (opcode & 0x7);
 
+            if (Arm32.arch == .v5te and op == 0b11 and h1 == 0b1) {
+                // BLX
+                const rm = rs;
+
+                cpu.r[14] = (cpu.r[15] - 2) | 1;
+                cpu.cpsr.t.write(cpu.r[rm] & 1 == 1);
+
+                cpu.r[15] = cpu.r[rm] & ~@as(u32, 1);
+                cpu.pipe.reload(cpu);
+            }
+
             const op1 = cpu.r[rd];
             const op2 = cpu.r[rs];
 

src/arm/v4t.zig

@@ -205,12 +205,9 @@ pub const thumb = struct {
                             const cond = i >> 2 & 0xF;
                             break :blk branch.fmt16(InstrFn, cond);
                         },
-                        0b110 => branch.fmt18(
+                        0b110, 0b111 => blk: {
-                            InstrFn,
+                            const H = i >> 5 & 0x3;
-                        ),
+                            break :blk branch.linkExchange(InstrFn, H);
-                        0b111 => blk: {
-                            const is_low = i >> 5 & 1 == 1;
-                            break :blk branch.fmt19(InstrFn, is_low);
                         },
                     },
                 };

src/arm/v5te.zig

@@ -149,6 +149,8 @@ pub const thumb = struct {
         return comptime comptime_blk: {
             @setEvalBranchQuota(5025); // This is exact
             var table = [_]InstrFn{und} ** 0x400;
+            //  9  8  7  6  5  4  3  2  1  0
+            // 15 14 13 12 11 10  9  8  7  6
 
             for (&table, 0..) |*handler, i| {
                 handler.* = switch (@as(u3, i >> 7 & 0x7)) {
@@ -230,12 +232,9 @@ pub const thumb = struct {
                             const cond = i >> 2 & 0xF;
                             break :blk branch.fmt16(InstrFn, cond);
                         },
-                        0b110 => branch.fmt18(
+                        0b110, 0b111 => blk: {
-                            InstrFn,
+                            const H = i >> 5 & 0x3;
-                        ),
+                            break :blk branch.linkExchange(InstrFn, H);
-                        0b111 => blk: {
-                            const is_low = i >> 5 & 1 == 1;
-                            break :blk branch.fmt19(InstrFn, is_low);
                         },
                     },
                 };