Port flexible array members to GCC + valgrind

These changes are needed to conform to the C standard's rule for
allocating structs containing flexible array members.  C11 says
that malloc (offsetof (struct s, m) + n) does not suffice to
allocate a struct with an n-byte tail; instead, malloc’s arg
should be rounded up to the nearest multiple of alignof (struct s).
Although this is arguably a defect in C11, gcc -O2 + valgrind
sometimes complains when this rule is violated, and when debugging
it’s better to keep valgrind happy.
For details please see the thread containing the message at:
https://gcc.gnu.org/ml/gcc-patches/2016-09/msg00416.html
* lib-src/ebrowse.c, src/alloc.c, src/image.c, src/process.c:
Include flexmember.h.
* lib-src/ebrowse.c (add_sym, add_member, make_namespace)
(register_namespace_alias):
* src/alloc.c (SDATA_SIZE, allocate_string_data):
* src/image.c (xpm_cache_color, imagemagick_create_cache):
* src/process.c (Fmake_network_process):
Use FLEXSIZEOF instead of offsetof and addition.
* src/alloc.c (SDATA_SIZE, vector_alignment):
Use FLEXALIGNOF instead of sizeof (ptrdiff_t).
* src/lisp.h (ALIGNOF_STRUCT_LISP_VECTOR):
Remove, as alloc.c can now calculate this on its own.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/process.c b/src/process.c
index 989511967ce..29bf43e0f29 100644
--- a/src/process.c
+++ b/src/process.c
@@ -88,6 +88,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #endif
 
 #include <c-ctype.h>
+#include <flexmember.h>
 #include <sig2str.h>
 #include <verify.h>
 
@@ -3807,8 +3808,8 @@ usage: (make-network-process &rest ARGS)  */)
         struct gaicb gaicb;
         struct addrinfo hints;
         char str[FLEXIBLE_ARRAY_MEMBER];
-      } *req = xmalloc (offsetof (struct req, str)
-                        + hostlen + 1 + portstringlen + 1);
+      } *req = xmalloc (FLEXSIZEOF (struct req, str,
+                                    hostlen + 1 + portstringlen + 1));
       dns_request = &req->gaicb;
       dns_request->ar_name = req->str;
       dns_request->ar_service = req->str + hostlen + 1;