start of x86-64 implementation; stack pushing, sinking, add with overflow, procedure return ops

src/arch/x86-64.zig

@@ -0,0 +1,91 @@
+// Execution thread convention:
+// rdi <- binary thread
+
+// Resources used:
+// https://mort.coffee/home/fast-interpreters/
+// https://blog.reverberate.org/2021/04/21/musttail-efficient-interpreters.html
+// https://en.wikibooks.org/wiki/X86_Assembly/GNU_assembly_syntax
+// https://www.cs.princeton.edu/courses/archive/spr18/cos217/lectures/15_AssemblyFunctions.pdf
+// https://ziglang.org/documentation/master/#toc-Assembly
+// https://csiflabs.cs.ucdavis.edu/~ssdavis/50/att-syntax.htm
+
+pub const Word = u64;
+
+// todo: Variant that pushes array of words.
+/// (iw | -- iw)
+pub fn opPushWord() callconv(.Naked) noreturn {
+    asm volatile (
+        \\ add $0x10, %%rdi
+        \\ pushq -8(%%rdi)
+        \\ jmpq *(%%rdi)
+    );
+}
+
+// todo: Variant that discards array of words.
+/// (w --)
+pub fn opSinkWord() callconv(.Naked) noreturn {
+    asm volatile (
+        \\ add $0x08, %%rdi
+        \\ addq $0x08, %%rsp
+        \\ jmpq *(%%rdi)
+    );
+}
+
+/// (iw | -- (iw'nth word from stack) )
+// fn opTakeWord(binary: [*]const Word, cond: bool) noreturn {
+//     @setRuntimeSafety(false);
+//     takeWord(binary[1].word);
+//     @call(.always_tail, binary[2].function, .{ &binary[2], cond });
+// }
+
+/// (iw | w)
+// fn opSetWord(binary: [*]const Word, cond: bool) noreturn {
+//     @setRuntimeSafety(false);
+//     setWord(binary[1].word, popWord());
+//     @call(.always_tail, binary[2].function, .{ &binary[2], cond });
+// }
+
+// todo: Generate operation permutations procedurally.
+// todo: Jump on overflow instead of cond setting?
+/// (w1 w2 -- sum overflow)
+pub fn opSumWordsWithOverflow() callconv(.Naked) noreturn {
+    // https://www.felixcloutier.com/x86/adc
+    // https://www.felixcloutier.com/x86/setcc
+    // idea: Could https://www.felixcloutier.com/x86/cmovcc be better for overflow push?
+    asm volatile (
+        \\ movq (%%rsp), %%rax
+        \\ adcq 8(%%rsp), %%rax
+        \\ movq %%rax, 8(%%rsp)
+        \\ setc %%al
+        \\ movb %%al, 7(%%rsp)
+        \\ addq $0x08, %%rdi
+        \\ jmpq *(%%rdi)
+    );
+}
+
+// todo: Generate operation permutations procedurally.
+// todo: We might not need cond register if conditions and jumps are combined?
+/// (w1 w2)
+// fn opRelativeJumpIfGreaterThan(binary: [*]const Word, cond: bool) noreturn {
+//     @setRuntimeSafety(false);
+//     const offset = if (popWord() > popWord()) binary[1].word else 2;
+//     @call(.always_tail, binary[offset].function, .{ &binary[offset], cond });
+// }
+
+/// (addr)
+pub fn opReturn() callconv(.Naked) noreturn {
+    // https://www.felixcloutier.com/x86/ret
+    asm volatile ("ret");
+}
+
+pub fn execute(binary: []const Word, entry_addr: usize) void {
+    // todo: Ensure correctness.
+    // https://wiki.osdev.org/System_V_ABI
+    // https://www.felixcloutier.com/x86/call
+    asm volatile (
+        \\ call *(%%rdi)
+        :
+        : [thread] "rdi" (&binary[entry_addr]),
+        : "rflags", "rax", "rbx", "rsp", "rbp", "r12", "r13", "r14", "r15", "rsi", "rdx", "rcx", "r8", "r9", "r10", "r11", "memory"
+    );
+}

src/interpreter.zig

@@ -0,0 +1,17 @@
+// todo: Interpreter context as binary local variable.
+//       It would hold memory mappings, as well as error stack.
+// todo: Define procedure call for user code.
+// todo: Instruction set extensions, such as memory management schemes, non-exhaustive logging,
+//       exception mechanism, coroutines via yield/resume and etc.
+// todo: Threading scheme.
+// todo: Extension for native floating point stack ops.
+// todo: Try using small code model with nopie/nopic binary.
+
+// idea: Specialized opcodes that have side effects on read and write, such as
+//       zero-check on push/pop, or jump if condition bit met. This would create a lot
+//       of permutations tho, we might try to discover which code devices are most used.
+
+// idea: 'JIT' could be done by simple op* compiled binary copying up until `jmpq *(%%rdi)`,
+//       with immediate operand prelude modified, which could be done procedurally.
+
+usingnamespace @import("arch/x86-64.zig");

src/main.zig

@@ -0,0 +1,16 @@
+const int = @import("interpreter.zig");
+
+pub fn main() !void {
+    const binary = [_]int.Word{
+        @as(int.Word, @intFromPtr(&int.opPushWord)),
+        ~@as(int.Word, 1),
+        @as(int.Word, @intFromPtr(&int.opPushWord)),
+        ~@as(int.Word, 1),
+        @as(int.Word, @intFromPtr(&int.opSumWordsWithOverflow)),
+        @as(int.Word, @intFromPtr(&int.opSinkWord)),
+        @as(int.Word, @intFromPtr(&int.opSinkWord)),
+        @as(int.Word, @intFromPtr(&int.opReturn)),
+    };
+
+    int.execute(&binary, 0);
+}