fuzz: Hide conflicts with cstdlib and use clang++ for linking.

This creates a build target called libec.a by setting the visibility
of functions that conflict with cstdlib to hidden. It then links
those symbols locally into one large object file that makes up libec.a

Fuzzing targets are linked against libec.a so that they can invoke ec
functionality while depending on outside libraries that need cstdlib.
When linking a particular object against cstdlib, to avoid conflicting
function declarations put the following before any includes from the
ec codebase:
   #define __stdlib_compat(...)

The fuzzing targets are now linked using clang++, so that c++ libraries
and objects can be used as part of the fuzzers.

BRANCH=none
BUG=chromium:876582
TEST=make -j buildfuzztests &&
  ./build/host/host_command_fuzz/host_command_fuzz.exe

Change-Id: Ifdfdc6a51c6ef23b4e192b013ca993bf48a4411b
Signed-off-by: Allen Webb <allenwebb@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1180401
Reviewed-by: Randall Spangler <rspangler@chromium.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/common.h b/include/common.h
index dac0bf2f00..f6bf9b1308 100644
--- a/include/common.h
+++ b/include/common.h
@@ -215,6 +215,17 @@ enum ec_error_list {
 #define test_export_static static
 #endif
 
+/*
+ * Mark functions that collide with stdlib so they can be hidden when linking
+ * against libraries that require stdlib. HIDE_EC_STDLIB should be defined
+ * before including common.h from code that links to cstdlib.
+ */
+#ifdef TEST_FUZZ
+#define __stdlib_compat __attribute__((visibility("hidden")))
+#else /* TEST_FUZZ */
+#define __stdlib_compat
+#endif /* TEST_FUZZ */
+
 /* find the most significant bit. Not defined in n == 0. */
 #define __fls(n) (31 - __builtin_clz(n))