gcc/ChangeLog:

	* doc/extend.texi (attribute alias, weak, weakref): Mention that
	the target of an alias must have the same type as the alias itself.

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index ec99c38a607..6f602140bfa 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2558,7 +2558,9 @@ __attribute__ ((access (write_only, 1, 2), access (read_write, 3))) int fgets (c
 @item alias ("@var{target}")
 @cindex @code{alias} function attribute
 The @code{alias} attribute causes the declaration to be emitted as an
-alias for another symbol, which must be specified.  For instance,
+alias for another symbol, which must have been previously declared with
+the same type.  Declaring an alias with a different type than the target
+is undefined and may be diagnosed.  For instance,
 
 @smallexample
 void __f () @{ /* @r{Do something.} */; @}
@@ -3922,9 +3924,10 @@ results in warning on line 5.
 The @code{weak} attribute causes the declaration to be emitted as a weak
 symbol rather than a global.  This is primarily useful in defining
 library functions that can be overridden in user code, though it can
-also be used with non-function declarations.  Weak symbols are supported
-for ELF targets, and also for a.out targets when using the GNU assembler
-and linker.
+also be used with non-function declarations.  The overriding symbol must
+have the same type as the declaration of the weak symbol.  Weak symbols
+are supported for ELF targets, and also for a.out targets when using
+the GNU assembler and linker.
 
 @item weakref
 @itemx weakref ("@var{target}")
@@ -3932,7 +3935,8 @@ and linker.
 The @code{weakref} attribute marks a declaration as a weak reference.
 Without arguments, it should be accompanied by an @code{alias} attribute
 naming the target symbol.  Optionally, the @var{target} may be given as
-an argument to @code{weakref} itself.  In either case, @code{weakref}
+an argument to @code{weakref} itself.  The the @var{target} must have
+the same type as the declaration.  In either case, @code{weakref}
 implicitly marks the declaration as @code{weak}.  Without a
 @var{target}, given as an argument to @code{weakref} or to @code{alias},
 @code{weakref} is equivalent to @code{weak}.
@@ -3951,7 +3955,9 @@ definition to be given for the target symbol.  If the target symbol is
 only referenced through weak references, then it becomes a @code{weak}
 undefined symbol.  If it is directly referenced, however, then such
 strong references prevail, and a definition is required for the
-symbol, not necessarily in the same translation unit.
+symbol, not necessarily in the same translation unit.  The definition
+must have the same type as the alias, otherwise the behavior is
+undefined.
 
 The effect is equivalent to moving all references to the alias to a
 separate translation unit, renaming the alias to the aliased symbol,