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.

4 files changed, 20 insertions, 27 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 67187f12ea6..5bbd5e55c42 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -46,6 +46,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include TERM_HEADER
 #endif /* HAVE_WINDOW_SYSTEM */
 
+#include <flexmember.h>
 #include <verify.h>
 #include <execinfo.h>           /* For backtrace.  */
 
@@ -1757,27 +1758,23 @@ static char const string_overrun_cookie[GC_STRING_OVERRUN_COOKIE_SIZE] =
 
 #ifdef GC_CHECK_STRING_BYTES
 
-#define SDATA_SIZE(NBYTES)                      \
-     ((SDATA_DATA_OFFSET                        \
-       + (NBYTES) + 1                           \
-       + sizeof (ptrdiff_t) - 1)                \
-      & ~(sizeof (ptrdiff_t) - 1))
+#define SDATA_SIZE(NBYTES) FLEXSIZEOF (struct sdata, data, NBYTES)
 
 #else /* not GC_CHECK_STRING_BYTES */
 
 /* The 'max' reserves space for the nbytes union member even when NBYTES + 1 is
    less than the size of that member.  The 'max' is not needed when
-   SDATA_DATA_OFFSET is a multiple of sizeof (ptrdiff_t), because then the
-   alignment code reserves enough space.  */
+   SDATA_DATA_OFFSET is a multiple of FLEXALIGNOF (struct sdata),
+   because then the alignment code reserves enough space.  */
 
 #define SDATA_SIZE(NBYTES)                                    \
      ((SDATA_DATA_OFFSET                                      \
-       + (SDATA_DATA_OFFSET % sizeof (ptrdiff_t) == 0         \
+       + (SDATA_DATA_OFFSET % FLEXALIGNOF (struct sdata) == 0 \
           ? NBYTES                                            \
-          : max (NBYTES, sizeof (ptrdiff_t) - 1))             \
+          : max (NBYTES, FLEXALIGNOF (struct sdata) - 1))     \
        + 1                                                    \
-       + sizeof (ptrdiff_t) - 1)                              \
-      & ~(sizeof (ptrdiff_t) - 1))
+       + FLEXALIGNOF (struct sdata) - 1)                      \
+      & ~(FLEXALIGNOF (struct sdata) - 1))
 
 #endif /* not GC_CHECK_STRING_BYTES */
 
@@ -1997,7 +1994,7 @@ allocate_string_data (struct Lisp_String *s,
 
   if (nbytes > LARGE_STRING_BYTES)
     {
-      size_t size = offsetof (struct sblock, data) + needed;
+      size_t size = FLEXSIZEOF (struct sblock, data, needed);
 
 #ifdef DOUG_LEA_MALLOC
       if (!mmap_lisp_allowed_p ())
@@ -2953,15 +2950,15 @@ set_next_vector (struct Lisp_Vector *v, struct Lisp_Vector *p)
 enum
   {
     /* Alignment of struct Lisp_Vector objects.  */
-    vector_alignment = COMMON_MULTIPLE (ALIGNOF_STRUCT_LISP_VECTOR,
-                                        GCALIGNMENT),
+    vector_alignment = COMMON_MULTIPLE (FLEXALIGNOF (struct Lisp_Vector),
+                                         GCALIGNMENT),
 
     /* Vector size requests are a multiple of this.  */
     roundup_size = COMMON_MULTIPLE (vector_alignment, word_size)
   };
 
 /* Verify assumptions described above.  */
-verify ((VECTOR_BLOCK_SIZE % roundup_size) == 0);
+verify (VECTOR_BLOCK_SIZE % roundup_size == 0);
 verify (VECTOR_BLOCK_SIZE <= (1 << PSEUDOVECTOR_SIZE_BITS));
 
 /* Round up X to nearest mult-of-ROUNDUP_SIZE --- use at compile time.  */
diff --git a/src/image.c b/src/image.c
index 7a554ef1b63..f15c2788967 100644
--- a/src/image.c
+++ b/src/image.c
@@ -30,7 +30,9 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #endif
 
 #include <setjmp.h>
+
 #include <c-ctype.h>
+#include <flexmember.h>
 
 #include "lisp.h"
 #include "frame.h"
@@ -3347,7 +3349,7 @@ xpm_cache_color (struct frame *f, char *color_name, XColor *color, int bucket)
   if (bucket < 0)
     bucket = xpm_color_bucket (color_name);
 
-  nbytes = offsetof (struct xpm_cached_color, name) + strlen (color_name) + 1;
+  nbytes = FLEXSIZEOF (struct xpm_cached_color, name, strlen (color_name) + 1);
   p = xmalloc (nbytes);
   strcpy (p->name, color_name);
   p->color = *color;
@@ -8328,8 +8330,8 @@ static struct animation_cache *
 imagemagick_create_cache (char *signature)
 {
   struct animation_cache *cache
-    = xmalloc (offsetof (struct animation_cache, signature)
-               + strlen (signature) + 1);
+    = xmalloc (FLEXSIZEOF (struct animation_cache, signature,
+                           strlen (signature) + 1));
   cache->wand = 0;
   cache->index = 0;
   cache->next = 0;
diff --git a/src/lisp.h b/src/lisp.h
index 97c8d9fe84f..29ed9fe8a2d 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -1429,13 +1429,6 @@ struct Lisp_Vector
     Lisp_Object contents[FLEXIBLE_ARRAY_MEMBER];
   };
 
-/* C11 prohibits alignof (struct Lisp_Vector), so compute it manually.  */
-enum
-  {
-    ALIGNOF_STRUCT_LISP_VECTOR
-      = alignof (union { struct vectorlike_header a; Lisp_Object b; })
-  };
-
 /* A boolvector is a kind of vectorlike, with contents like a string.  */
 
 struct Lisp_Bool_Vector
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;