1 files changed, 24 insertions, 9 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 9cbc7473fc1..7a3e0d6a8a3 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4603,14 +4603,29 @@ verify (sizeof (struct Lisp_Cons) == sizeof (union Aligned_Cons));
 
 # define USE_LOCAL_ALLOCATORS
 
+/* Alignment fixup needed for alloca.  GCC aligns alloca properly already,
+   Clang sometimes doesn't, and play it safe for other random compilers.  */
+# if __GNUC__ && !__clang__
+enum { ALLOCA_FIXUP = 0 };
+# else
+enum { ALLOCA_FIXUP = GCALIGNMENT - 1 };
+# endif
+
+/* Declare a void * variable PTR and set it to a properly-aligned array of
+   N newly allocated bytes with function lifetime.  */
+# define LOCAL_ALLOCA(ptr, n)                           \
+    void *ptr = alloca ((n) + ALLOCA_FIXUP);            \
+    ptr = (void *) ((intptr_t) ptr_ & ~(ALLOCA_FIXUP))
+
 /* Return a function-scoped cons whose car is X and cdr is Y.  */
 
 # define local_cons(x, y)                                               \
     ({                                                                  \
-       struct Lisp_Cons *c = alloca (sizeof (struct Lisp_Cons));        \
-       c->car = (x);                                                    \
-       c->u.cdr = (y);                                                  \
-       make_lisp_ptr (c, Lisp_Cons);                                    \
+       LOCAL_ALLOCA (ptr_, sizeof (struct Lisp_Cons));                  \
+       struct Lisp_Cons *c_ = ptr_;                                     \
+       c_->car = (x);                                                   \
+       c_->u.cdr = (y);                                                 \
+       make_lisp_ptr (c_, Lisp_Cons);                                   \
     })
 
 # define local_list1(x) local_cons (x, Qnil)
@@ -4625,9 +4640,9 @@ verify (sizeof (struct Lisp_Cons) == sizeof (union Aligned_Cons));
        ptrdiff_t size_ = size;                                          \
        Lisp_Object init_ = init;                                        \
        Lisp_Object vec_;                                                \
-       if (size_ <= (MAX_ALLOCA - header_size) / word_size)             \
+       if (size_ <= (MAX_ALLOCA - ALLOCA_FIXUP - header_size) / word_size) \
          {                                                              \
-           void *ptr_ = alloca (size_ * word_size + header_size);       \
+           LOCAL_ALLOCA (ptr_, size_ * word_size + header_size);        \
            vec_ = local_vector_init (ptr_, size_, init_);               \
          }                                                              \
        else                                                             \
@@ -4642,10 +4657,10 @@ verify (sizeof (struct Lisp_Cons) == sizeof (union Aligned_Cons));
        char const *data_ = data;                                        \
        ptrdiff_t nbytes_ = nbytes;                                      \
        Lisp_Object string_;                                             \
-       if (nbytes_ <= MAX_ALLOCA - sizeof (struct Lisp_String) - 1)     \
+       if (nbytes_                                                      \
+           <= MAX_ALLOCA - ALLOCA_FIXUP - sizeof (struct Lisp_String) - 1) \
          {                                                              \
-           struct Lisp_String *ptr_                                     \
-             = alloca (sizeof (struct Lisp_String) + 1 + nbytes_);      \
+           LOCAL_ALLOCA (ptr_, sizeof (struct Lisp_String) + 1 + bytes_); \
            string_ = local_string_init (ptr_, data_, nbytes_);          \
          }                                                              \
        else                                                             \