compiler: fix try/catch miscompilation

When skipping catch blocks with exception variables, jump beyond the
instruction popping the exception variable off the stack to fix a
stack position mismatch between compiler and vm.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

2 files changed, 30 insertions, 2 deletions

diff --git a/compiler.c b/compiler.c
index 3c6f6e1..436f91d 100644
--- a/compiler.c
+++ b/compiler.c
@@ -2485,9 +2485,9 @@ uc_compiler_compile_try(uc_compiler *compiler)
 
 	uc_compiler_parse_consume(compiler, TK_RBRACE);
 
-	uc_compiler_set_jmpaddr(compiler, jmp_off, chunk->count);
-
 	uc_compiler_leave_scope(compiler);
+
+	uc_compiler_set_jmpaddr(compiler, jmp_off, chunk->count);
 }
 
 static void
diff --git a/tests/03_bugs/01_try_catch_stack_mismatch b/tests/03_bugs/01_try_catch_stack_mismatch
new file mode 100644
index 0000000..ae7c760
--- /dev/null
+++ b/tests/03_bugs/01_try_catch_stack_mismatch
@@ -0,0 +1,28 @@
+When compiling a try/catch statement with an exception variable, the catch
+skip jump incorrectly pointed to the POP instruction popping the exception
+variable off the stack, leading to a stack position mismatch between
+compiler and vm, causing local variables to yield wrong values at runtime.
+
+-- Expect stdout --
+1
+-- End --
+
+-- Testcase --
+{%
+	function f() {
+		let x;
+
+		try {
+			x = 1;
+		}
+		catch(e) {
+
+		}
+
+		// Before the fix, `x` incorrectly yielded the print function value
+		print(x, "\n");
+	}
+
+	f()
+%}
+-- End --