diff --git a/compiler-rt/lib/profile/InstrProfilingPlatformLinux.c b/compiler-rt/lib/profile/InstrProfilingPlatformLinux.c
--- a/compiler-rt/lib/profile/InstrProfilingPlatformLinux.c
+++ b/compiler-rt/lib/profile/InstrProfilingPlatformLinux.c
@@ -18,6 +18,11 @@
 #include "InstrProfilingInternal.h"
 
 #if defined(__FreeBSD__) && !defined(ElfW)
+/*
+ * FreeBSD's elf.h and link.h headers do not define the ElfW(type) macro yet.
+ * If this is added to all supported FreeBSD versions in the future, this
+ * compatibility macro can be removed.
+ */
 #define ElfW(type) __ElfN(type)
 #endif