Fixes to afl-cc and documentation (#1974)

* Always compile with -ldl when building for CODE_COVERAGE

When building with CODE_COVERAGE, the afl runtime contains code that
calls `dladdr` which requires -ldl. Under most circumstances, clang
already adds this (e.g. when building with pc-table), but there are some
circumstances where it isn't added automatically.

* Add visibility declaration to __afl_connected

When building with hidden visibility, the use of __AFL_LOOP inside such
code can cause linker errors due to __afl_connected being declared
"hidden".

* Update docs to clarify that CODE_COVERAGE=1 is required for dynamic_covfilter

1 files changed, 6 insertions, 1 deletions

diff --git a/src/afl-cc.c b/src/afl-cc.c
index 73487188..d11419b0 100644
--- a/src/afl-cc.c
+++ b/src/afl-cc.c
@@ -1521,7 +1521,7 @@ void add_defs_persistent_mode(aflcc_state_t *aflcc) {
       "({ static volatile const char *_B __attribute__((used,unused)); "
       " _B = (const char*)\"" PERSIST_SIG
       "\"; "
-      "extern int __afl_connected;"
+      "extern __attribute__((visibility(\"default\"))) int __afl_connected;"
 #ifdef __APPLE__
       "__attribute__((visibility(\"default\"))) "
       "int _L(unsigned int) __asm__(\"___afl_persistent_loop\"); "
@@ -2311,6 +2311,11 @@ void add_runtime(aflcc_state_t *aflcc) {
 
     }
 
+  #if __AFL_CODE_COVERAGE
+    // Required for dladdr used in afl-compiler-rt.o
+    insert_param(aflcc, "-ldl");
+  #endif
+
   #if !defined(__APPLE__) && !defined(__sun)
     if (!aflcc->shared_linking && !aflcc->partial_linking)
       insert_object(aflcc, "dynamic_list.txt", "-Wl,--dynamic-list=%s", 0);