Index: docs/ld.lld.1
===================================================================
--- docs/ld.lld.1
+++ docs/ld.lld.1
@@ -50,6 +50,7 @@
 Generate a build ID note.
 .Ar value
 may be one of
+.Cm fast ,
 .Cm md5 ,
 .Cm sha1 ,
 .Cm tree ,
@@ -61,13 +62,17 @@
 is an alias for
 .Cm sha1 .
 Build-IDs of type
+.Cm fast ,
 .Cm md5 ,
 .Cm sha1 ,
 and
 .Cm tree
 are calculated from the object contents.
+.Cm fast
+is not intended to be cryptographically secure.
 .It Fl -build-id
-Generate a build ID note.
+Synonym for
+.Fl -build-id= Ns Cm fast .
 .It Fl -color-diagnostics= Ns Ar value
 Use colors in diagnostics.
 .Ar value