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

[Steve Ellcey]

On Wed, 2017-09-20 at 08:37 -0700, Steve Ellcey wrote:
> 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

Martin,

I think there is more fallout from this patch. Â The libatomic library
can use ifuncs and right now it is not working on aarch64 (testing a
proposed patch I sent) because the ifunc check fails due to the new
warnings. Â I believe this can be reproduced with ToT on x86 or arm as
they use ifuncs in the checked in sources but I have not tried that
yet. Â Note that the build does not fail, it is just that the check for
ifunc support fails and thus the library is built without them.

Steve Ellcey
sellcey@cavium.com

configure:14698: checking whether the target supports the ifunc attribute
configure:14720: /home/sellcey/gcc-libatomic/obj/gcc/./gcc/xgcc
-B/home/sellcey/gcc-libatomic/obj/gcc/./gcc/ -B/home/sellcey/gcc-
libatomic/install/aarch64-unknown-linux-gnu/bin/ -B/home/sellcey/gcc-
libatomic/install/aarch64-unknown-linux-gnu/lib/ -isystem
/home/sellcey/gcc-libatomic/install/aarch64-unknown-linux-gnu/include
-isystem /home/sellcey/gcc-libatomic/install/aarch64-unknown-linux-
gnu/sys-include    -o conftest -g -O2  -pthread
-Werror   conftest.c  >&5
conftest.c:68:9: error: 'foo' 'ifunc' resolver should return a function
pointer [-Werror=attributes]
     int foo(void) __attribute__((ifunc("foo_sel")));
         ^~~
conftest.c:67:11: note: resolver declaration here
     void *foo_sel(void) { return foo_alt; }
           ^~~~~~~
cc1: all warnings being treated as errors
configure:14720: $? = 1