[PATCH] detect incompatible aliases (PR c/81854)

[Steve Ellcey]

On Tue, 2017-09-19 at 09:16 -0600, Martin Sebor wrote:
> On 09/18/2017 03:44 PM, Joseph Myers wrote:
> > 
> > On Mon, 18 Sep 2017, Martin Sebor wrote:
> > 
> > > 
> > > It's meant as an escape hatch.  It allows declaring compatibility
> > > symbols, for example by the libstdc++ _GLIBCXX_3_4_SYMVER macro
> > > defined in libstdc++-v3/src/c++98/compatibility.cc.  The macro is
> > > used to declare compatibility functions of all sorts of
> > > incompatible
> > > types.  The originally posted patch had libstdc++ disable the
> > > warning
> > > for the file with the symbols but Jonathan preferred this
> > > solution.
> > > 
> > > It could perhaps be tightened up to detect some of the cases on
> > > your
> > > list but I'm not sure it's worth the effort and added complexity.
> > > Let me know if you feel differently (or have a different
> > > suggestion),
> > > otherwise I will go ahead and commit the patch as is.
> > Please add a comment explaining this reasoning and commit the
> > patch.
> Done in r252976.
> 
> Thanks
> Martin

This patch is causing my gcc/glibc ToT build to fail on aarch64. Â I am
not sure if everything should be working at this point or not or if
there is more that needs to be done. Â The problem is with the memcpy,
memmove, etc. ifuncs on aarch64.

Steve Ellcey
sellcey@cavium.com


In file included from <command-line>:0:0:
../sysdeps/aarch64/multiarch/memmove.c:38:31: error: ‘memmove’ alias
between functions of incompatible types ‘void *(void *, const void *,
size_t) {aka void *(void *, const void *, long unsigned int)}’ and
‘void * (*(void))(void *, const void *, size_t) {aka void *
(*(void))(void *, const void *, long unsigned int)}’ [-
Werror=attributes]
 strong_alias (__libc_memmove, memmove);
                               ^~~~~~~
./../include/libc-symbols.h:135:26: note: in definition of macro
‘_strong_alias’
   extern __typeof (name) aliasname __attribute__ ((alias (#name)));
                          ^~~~~~~~~
../sysdeps/aarch64/multiarch/memmove.c:38:1: note: in expansion of
macro ‘strong_alias’
 strong_alias (__libc_memmove, memmove);
 ^~~~~~~~~~~~
In file included from <command-line>:0:0:
../sysdeps/aarch64/multiarch/memmove.c:34:13: note: aliased declaration
here
 libc_ifunc (__libc_memmove,
             ^~~~~~~~~~~~~~
./../include/libc-symbols.h:800:25: note: in definition of macro
‘__ifunc_resolver’

   __typeof (type_name) *name##_ifunc (arg)    \
                         ^~~~
./../include/libc-symbols.h:916:32: note: in expansion of macro
‘__ifunc’
 #define libc_ifunc(name, expr) __ifunc (name, name, expr, void,
INIT_ARCH)
                                ^~~~~~~
../sysdeps/aarch64/multiarch/memmove.c:34:1: note: in expansion of
macro ‘libc_ifunc’
 libc_ifunc (__libc_memmove,
 ^~~~~~~~~~
cc1: all warnings being treated as errors