[compiler-rt][msan] Ensure initialisation before calling __msan_unpoison

[Hahnfeld]

Summary

__msan_unpoison uses intercepted memset which currently leads to a SEGV when linking with libc++ under CentOS 7.

[eugenis]

LGTM, thanks!

compiler-rt/trunk/lib/msan/msan_interceptors.cc

 #define COMMON_INTERCEPTOR_WRITE_RANGE(ctx, ptr, size) \
   __msan_unpoison(ptr, size)
 #define COMMON_INTERCEPTOR_READ_RANGE(ctx, ptr, size) \
   CHECK_UNPOISONED_CTX(ctx, ptr, size)
 #define COMMON_INTERCEPTOR_INITIALIZE_RANGE(ptr, size) \
   __msan_unpoison(ptr, size)
 #define COMMON_INTERCEPTOR_ENTER(ctx, func, ...)                  \
   if (msan_init_is_running) return REAL(func)(__VA_ARGS__);       \
+  ENSURE_MSAN_INITED();                                           \
   MSanInterceptorContext msan_ctx = {IsInInterceptorScope()};     \
   ctx = (void *)&msan_ctx;                                        \
   (void)ctx;                                                      \
   InterceptorScope interceptor_scope;                             \
-  __msan_unpoison(__errno_location(), sizeof(int)); /* NOLINT */  \
-  ENSURE_MSAN_INITED();
+  __msan_unpoison(__errno_location(), sizeof(int)); /* NOLINT */
 #define COMMON_INTERCEPTOR_DIR_ACQUIRE(ctx, path) \
   do {                                            \
   } while (false)
 #define COMMON_INTERCEPTOR_FD_ACQUIRE(ctx, fd) \
   do {                                         \
   } while (false)
 #define COMMON_INTERCEPTOR_FD_RELEASE(ctx, fd) \
   do {                                         \