From 207379165f277cba25e3fce9032d93d6d66239a3 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Tue, 18 May 2021 00:23:41 +0430
Subject: [PATCH] LibWasm: Fix nested structured instruction parsing

Previously, the ip would not be propagated correctly, and we would
produce invalid jumps when more than one level of nesting was involved.
This makes loops work :P
---
 .../Libraries/LibWasm/AbstractMachine/Interpreter.cpp | 11 +++++++----
 Userland/Libraries/LibWasm/Parser/Parser.cpp          |  9 +++++----
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/Userland/Libraries/LibWasm/AbstractMachine/Interpreter.cpp b/Userland/Libraries/LibWasm/AbstractMachine/Interpreter.cpp
index a1d39387ec..fa3dd06900 100644
--- a/Userland/Libraries/LibWasm/AbstractMachine/Interpreter.cpp
+++ b/Userland/Libraries/LibWasm/AbstractMachine/Interpreter.cpp
@@ -28,10 +28,12 @@ void Interpreter::interpret(Configuration& configuration)
 
     while (current_ip_value < max_ip_value) {
         auto& instruction = instructions[current_ip_value.value()];
+        auto old_ip = current_ip_value;
         interpret(configuration, current_ip_value, instruction);
         if (m_do_trap)
             return;
-        ++current_ip_value;
+        if (current_ip_value == old_ip) // If no jump occurred
+            ++current_ip_value;
     }
 }
 
@@ -46,18 +48,19 @@ void Interpreter::branch_to_label(Configuration& configuration, LabelIndex index
     size_t drop_count = index.value() + 1;
 
     for (; !configuration.stack().is_empty();) {
-        auto entry = configuration.stack().pop();
+        auto& entry = configuration.stack().peek();
         if (entry.has<NonnullOwnPtr<Label>>()) {
             if (drop_count-- == 0)
                 break;
         }
+        configuration.stack().pop();
     }
 
     // Push results in reverse
     for (size_t i = results.size(); i > 0; --i)
         configuration.stack().push(move(static_cast<Vector<NonnullOwnPtr<Value>>&>(results)[i - 1]));
 
-    configuration.ip() = label->continuation() + 1;
+    configuration.ip() = label->continuation();
 }
 
 ReadonlyBytes Interpreter::load_from_memory(Configuration& configuration, const Instruction& instruction, size_t size)
@@ -321,7 +324,7 @@ void Interpreter::interpret(Configuration& configuration, InstructionPointer& ip
         auto& args = instruction.arguments().get<Instruction::StructuredInstructionArgs>();
         if (args.block_type.kind() != BlockType::Empty)
             arity = 1;
-        configuration.stack().push(make<Label>(arity, ip.value() + 1));
+        configuration.stack().push(make<Label>(arity, ip.value()));
         return;
     }
     case Instructions::if_.value(): {
diff --git a/Userland/Libraries/LibWasm/Parser/Parser.cpp b/Userland/Libraries/LibWasm/Parser/Parser.cpp
index 5a6ab098be..bfe32b84a6 100644
--- a/Userland/Libraries/LibWasm/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWasm/Parser/Parser.cpp
@@ -82,7 +82,7 @@ struct ParseUntilAnyOfResult {
     Vector<T> values;
 };
 template<typename T, u8... terminators, typename... Args>
-static ParseResult<ParseUntilAnyOfResult<T>> parse_until_any_of(InputStream& stream, Args... args) requires(requires(InputStream& stream, Args... args) { T::parse(stream, args...); })
+static ParseResult<ParseUntilAnyOfResult<T>> parse_until_any_of(InputStream& stream, Args&... args) requires(requires(InputStream& stream, Args... args) { T::parse(stream, args...); })
 {
     ScopeLogger<WASM_BINPARSER_DEBUG> logger;
     ReconsumableStream new_stream { stream };
@@ -305,7 +305,8 @@ ParseResult<Vector<Instruction>> Instruction::parse(InputStream& stream, Instruc
                 result.value().values.append(Instruction { Instructions::structured_end });
 
                 // Transform op(..., instr*) -> op(...) instr* op(end(ip))
-                result.value().values.prepend(Instruction { opcode, StructuredInstructionArgs { BlockType { block_type.release_value() }, ++ip, {} } });
+                result.value().values.prepend(Instruction { opcode, StructuredInstructionArgs { BlockType { block_type.release_value() }, ip.value(), {} } });
+                ++ip;
                 return result.release_value().values;
             }
 
@@ -314,7 +315,7 @@ ParseResult<Vector<Instruction>> Instruction::parse(InputStream& stream, Instruc
             instructions.append(result.release_value().values);
             instructions.append(Instruction { Instructions::structured_else });
             ++ip;
-            else_ip = ip;
+            else_ip = ip.value();
         }
         // if with else
         {
@@ -324,7 +325,7 @@ ParseResult<Vector<Instruction>> Instruction::parse(InputStream& stream, Instruc
             instructions.append(result.release_value().values);
             instructions.append(Instruction { Instructions::structured_end });
             ++ip;
-            end_ip = ip;
+            end_ip = ip.value();
         }
 
         instructions.prepend(Instruction { opcode, StructuredInstructionArgs { BlockType { block_type.release_value() }, end_ip, else_ip } });