GCC diagnoses declarations of function aliases whose type doesn't
match that of the target (ditto for attribute weakref). It doesn't
yet diagnose such incompatbilities for variable aliases but that's
just an oversight that I will try to remember to correct in GCC 11.
The attached patch updates the manual to make it clear that
aliases must have the same type as their targets, or the behavior
is undefined (and may be diagnosed).
Martin
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,
