From: Felix Fietkau <nbd@nbd.name>
Date: Mon, 6 Jul 2026 11:12:32 +0200
Subject: [PATCH] compiler: prevent unbounded recompilation on failed
 module imports

A source's exports.offset of -1 marks a module whose compilation has been
entered but not completed. When a module failed to compile, uc_compiler_finish
freed its function and the error cascaded up through the importers via error
recovery, leaving each involved source at offset -1 with its function gone. The
re-entry guard only recognised an in-progress module by finding its function, so
those freed modules were recompiled again on every subsequent import. Across a
wide import graph this recompilation multiplies and the compiler appears to hang.

Detect the offset -1 marker directly instead of relying on the presence of a
function: report a circular dependency when the function is still around, and
propagate the failure otherwise, rather than recursing into the module again.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

--- a/compiler.c
+++ b/compiler.c
@@ -3479,15 +3479,26 @@ uc_compiler_compile_module_source(uc_com
 
 	uc_program_function_foreach(compiler->program, fn) {
 		if (uc_program_function_source(fn) == source) {
-			if (source->exports.offset == (size_t)-1)
-				uc_compiler_syntax_error(compiler, compiler->parser->prev.pos,
-					"Circular dependency");
-
 			loaded = true;
 			break;
 		}
 	}
 
+	/* An offset of -1 marks a source whose compilation was entered but not yet
+	 * completed. Re-entering it is either a circular dependency (its function is
+	 * still present) or a module whose earlier compilation failed and freed its
+	 * function. Recompiling in either case recurses without bound across a large
+	 * import graph, so report the cycle and propagate the failure instead. */
+	if (source->exports.offset == (size_t)-1) {
+		if (loaded)
+			uc_compiler_syntax_error(compiler, compiler->parser->prev.pos,
+				"Circular dependency");
+		else if (errp)
+			xasprintf(errp, "Module previously failed to compile\n");
+
+		return false;
+	}
+
 	if (!loaded) {
 		/* We do not yet support linking precompiled modules at compile time,
 		   turn static import operation into dynamic load one. */