Make sure that statements such as:

  strcpy (dst, "/gnu/store/…");

or

  static const char str[] = "/gnu/store/…";
  …
  strcpy (dst, str);

do not result in chunked /gnu/store strings that are undetectable by
Guix's GC and its grafting code.  See <https://bugs.gnu.org/24703>
and <https://bugs.gnu.org/30395>.

diff --git a/gcc/builtins.c b/gcc/builtins.c
index d37d73fc4a0..dac33d9d29a 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -3282,6 +3282,58 @@ determine_block_size (tree len, rtx len_rtx,
 			  GET_MODE_MASK (GET_MODE (len_rtx)));
 }

+extern void debug_tree (tree);
+
+/* Return true if STR contains the string "/gnu/store".  */
+
+bool
+store_reference_p (tree str)
+{
+  if (getenv ("GUIX_GCC_DEBUG") != NULL)
+    debug_tree (str);
+
+  if (TREE_CODE (str) == ADDR_EXPR)
+    str = TREE_OPERAND (str, 0);
+
+  if (TREE_CODE (str) == VAR_DECL
+      && TREE_STATIC (str)
+      && TREE_READONLY (str))
+    {
+      /* STR may be a 'static const' variable whose initial value
+         is a string constant.  See <https://bugs.gnu.org/30395>.  */
+      str = DECL_INITIAL (str);
+      if (str == NULL_TREE)
+        return false;
+    }
+
+  if (TREE_CODE (str) != STRING_CST)
+    return false;
+
+  int len;
+  const char *store;
+
+  store = getenv ("NIX_STORE") ? getenv ("NIX_STORE") : "/gnu/store";
+  len = strlen (store);
+
+  /* Size of the hash part of store file names, including leading slash and
+     trailing hyphen.  */
+  const int hash_len = 34;
+
+  if (TREE_STRING_LENGTH (str) < len + hash_len)
+    return false;
+
+  /* We cannot use 'strstr' because 'TREE_STRING_POINTER' returns a string
+     that is not necessarily NUL-terminated.  */
+
+  for (int i = 0; i < TREE_STRING_LENGTH (str) - (len + hash_len); i++)
+    {
+      if (strncmp (TREE_STRING_POINTER (str) + i, store, len) == 0)
+	return true;
+    }
+
+  return false;
+}
+
 /* Try to verify that the sizes and lengths of the arguments to a string
    manipulation function given by EXP are within valid bounds and that
    the operation does not lead to buffer overflow or read past the end.
@@ -3839,6 +3891,13 @@ expand_builtin_memory_copy_args (tree dest, tree src, tree len,
   unsigned HOST_WIDE_INT max_size;
   unsigned HOST_WIDE_INT probable_max_size;

+  /* Do not emit block moves, which translate to the 'movabs' instruction on
+     x86_64, when SRC refers to store items.  That way, store references
+     remain visible to the Guix GC and grafting code.  See
+     <https://bugs.gnu.org/24703>.  */
+  if (store_reference_p (src))
+    return NULL_RTX;
+
   /* If DEST is not a pointer type, call the normal function.  */
   if (dest_align == 0)
     return NULL_RTX;
diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index f30818042ee..56b592f9335 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -656,6 +656,8 @@ var_decl_component_p (tree var)
 	      && TREE_CODE (TREE_OPERAND (inner, 0)) == ADDR_EXPR));
 }

+extern bool store_reference_p (tree);
+
 /* Return TRUE if the SIZE argument, representing the size of an
    object, is in a range of values of which exactly zero is valid.  */

@@ -748,6 +750,9 @@ gimple_fold_builtin_memory_op (gimple_stmt_iterator *gsi,
       off0 = build_int_cst (build_pointer_type_for_mode (char_type_node,
 							 ptr_mode, true), 0);

+      if (store_reference_p (src))
+        return false;
+
       /* If we can perform the copy efficiently with first doing all loads
          and then all stores inline it that way.  Currently efficiently
 	 means that we can load all the memory into a single integer
05</span></td><td><a href='/guix/commit/gnu/packages/electronics.scm?id=de3c03a47160dec355d9b19ad5ca210d90c15fd7'>Merge remote-tracking branch 'origin/master' into staging</a></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2020-07-25 18:47:55 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu/packages/electronics.scm?id=406f3f9b8afe77823b11932586e32e259f1b9242'>gnu: libsigrok: Remove unused input.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-07-25 16:16:11 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu/packages/electronics.scm?id=e1409c764f554b688efe07c04bf90198daeca258'>gnu: check: Update to 0.15.1.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>