OSS-Fuzz: Add new fuzzer targets assembly process (#1913)

Signed-off-by: Arthur SC Chan <arthur.chan@adalogics.com>

test/fuzzers/fuzz_asm.c

@@ -0,0 +1,61 @@
+#include <stddef.h>
+#include <stdint.h>
+#include <janet.h>
+
+#define MAX_ASM_INPUT 65536
+
+#ifdef JANET_ASSEMBLER
+static void assemble_forms(JanetParser *parser) {
+    while (janet_parser_has_more(parser)) {
+        Janet form = janet_parser_produce(parser);
+        janet_gcroot(form);
+
+        for (int mode = 0; mode < 2; mode++) {
+            JanetTryState try_state;
+            if (janet_try(&try_state) == JANET_SIGNAL_OK) {
+                int flags = mode ? JANET_ASSEMBLE_FLAG_OPTIMIZE : 0;
+                JanetAssembleResult result = janet_asm(form, flags);
+                (void)result;
+            }
+            janet_restore(&try_state);
+        }
+
+        janet_gcunroot(form);
+    }
+}
+#endif
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+#ifdef JANET_ASSEMBLER
+    if (size == 0 || size > MAX_ASM_INPUT) return 0;
+
+    janet_init();
+    JanetParser parser;
+    janet_parser_init(&parser);
+
+    JanetTryState try_state;
+    if (janet_try(&try_state) == JANET_SIGNAL_OK) {
+        for (size_t index = 0; index < size; index++) {
+            enum JanetParserStatus status = janet_parser_status(&parser);
+            if (status == JANET_PARSE_ERROR || status == JANET_PARSE_DEAD)
+                break;
+            janet_parser_consume(&parser, data[index]);
+            assemble_forms(&parser);
+        }
+
+        enum JanetParserStatus status = janet_parser_status(&parser);
+        if (status != JANET_PARSE_ERROR && status != JANET_PARSE_DEAD) {
+            janet_parser_eof(&parser);
+            assemble_forms(&parser);
+        }
+    }
+    janet_restore(&try_state);
+
+    janet_parser_deinit(&parser);
+    janet_deinit();
+#else
+    (void)data;
+    (void)size;
+#endif
+    return 0;
+}