test(relinker): check decoder lengths against an LLVM-generated table

Co-Authored-By: Claude Opus 5.5 <[email protected]>

core/relinker/codegen/tests/DecoderLengthTests.cpp

@@ -0,0 +1,64 @@
+#include "DecoderLengthCases.hpp"
+#include <codegen/CodegenException.hpp>
+#include <codegen/x86/X64InstructionDecoder.hpp>
+#include <cstdint>
+#include <iostream>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace {
+
+using Bytes = std::vector<std::uint8_t>;
+
+void require(bool condition, const std::string& message) {
+    if (!condition) throw std::runtime_error(message);
+}
+
+Bytes parse(std::string_view hex) {
+    Bytes bytes;
+    for (std::size_t index = 0; index + 1 < hex.size(); index += 2) {
+        bytes.push_back(static_cast<std::uint8_t>(std::stoul(std::string(hex.substr(index, 2)), nullptr, 16)));
+    }
+    return bytes;
+}
+
+std::size_t decodedLength(const Codegen::X64InstructionDecoder& decoder, const Bytes& bytes, const std::string& name) {
+    try {
+        return decoder.Decode(bytes.data(), bytes.size());
+    } catch (const Codegen::CodegenException& error) {
+        throw std::runtime_error("Cannot decode " + name + ": " + error.what());
+    }
+}
+
+bool truncationRejected(const Codegen::X64InstructionDecoder& decoder, const Bytes& bytes, std::size_t available) {
+    try {
+        (void)decoder.Decode(bytes.data(), available);
+    } catch (const Codegen::CodegenException&) {
+        return true;
+    }
+    return false;
+}
+
+}
+
+int main() {
+    try {
+        const Codegen::X64InstructionDecoder decoder;
+        for (const auto& testCase : kDecoderLengthCases) {
+            const std::string name = testCase.Bytes;
+            auto bytes = parse(testCase.Bytes);
+            require(bytes.size() == testCase.Length, "Decoder length case " + name + " does not hold its own length");
+            require(decodedLength(decoder, bytes, name) == testCase.Length, "Wrong length for " + name);
+            require(truncationRejected(decoder, bytes, bytes.size() - 1), "A truncated " + name + " was accepted");
+            bytes.insert(bytes.end(), 15, 0x90);
+            require(decodedLength(decoder, bytes, name + " followed by NOPs") == testCase.Length, "Wrong length for " + name + " followed by NOPs");
+        }
+        std::cout << "Decoder length tests passed\n";
+    } catch (const std::exception& error) {
+        std::cerr << error.what() << '\n';
+        return 1;
+    }
+    return 0;
+}