diff --git a/gnu/local.mk b/gnu/local.mk
index a0f40d13ae..7363655f38 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -814,6 +814,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/gcc-6-source-date-epoch-1.patch		\
   %D%/packages/patches/gcc-6-source-date-epoch-2.patch		\
   %D%/packages/patches/gcc-8-strmov-store-file-names.patch	\
+  %D%/packages/patches/gcc-9-strmov-store-file-names.patch	\
   %D%/packages/patches/gd-CVE-2018-5711.patch			\
   %D%/packages/patches/gd-CVE-2018-1000222.patch		\
   %D%/packages/patches/gd-CVE-2019-6977.patch			\
diff --git a/gnu/packages/commencement.scm b/gnu/packages/commencement.scm
index b07630a54d..a8ec677cee 100644
--- a/gnu/packages/commencement.scm
+++ b/gnu/packages/commencement.scm
@@ -1085,4 +1085,7 @@ and binaries, plus debugging symbols in the @code{debug} output), and Binutils."
 (define-public gcc-toolchain-8
   (make-gcc-toolchain gcc-8))

+(define-public gcc-toolchain-9
+  (make-gcc-toolchain gcc-9))
+
 ;;; commencement.scm ends here
diff --git a/gnu/packages/gcc.scm b/gnu/packages/gcc.scm
index b9a9583410..eefce2737b 100644
--- a/gnu/packages/gcc.scm
+++ b/gnu/packages/gcc.scm
@@ -519,6 +519,20 @@ It also includes runtime support libraries for these languages.")))
               (patches (search-patches "gcc-8-strmov-store-file-names.patch"
                                        "gcc-5.0-libvtv-runpath.patch"))))))

+(define-public gcc-9
+  (package
+   (inherit gcc-8)
+   (version "9.1.0")
+   (source (origin
+            (method url-fetch)
+            (uri (string-append "mirror://gnu/gcc/gcc-"
+                                version "/gcc-" version ".tar.xz"))
+            (sha256
+             (base32
+              "1817nc2bqdc251k0lpc51cimna7v68xjrnvqzvc50q3ax4s6i9kr"))
+            (patches (search-patches "gcc-9-strmov-store-file-names.patch"
+                                     "gcc-5.0-libvtv-runpath.patch"))))))
+
 ;; Note: When changing the default gcc version, update
 ;;       the gcc-toolchain-* definitions and the gfortran definition
 ;;       accordingly.
diff --git a/gnu/packages/patches/gcc-9-strmov-store-file-names.patch b/gnu/packages/patches/gcc-9-strmov-store-file-names.patch
new file mode 100644
index 0000000000..0c5d70491a
--- /dev/null
+++ b/gnu/packages/patches/gcc-9-strmov-store-file-names.patch
@@ -0,0 +1,114 @@
+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
