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Make sure that statements such as:
strcpy (dst, "/gnu/store/…");
do not result in chunked /gnu/store strings that are undetectable by
Guix's GC and its grafting code. See <http://bugs.gnu.org/24703>.
--- gcc-5.3.0/gcc/builtins.c 2016-10-18 10:50:46.080616285 +0200
+++ gcc-5.3.0/gcc/builtins.c 2016-11-09 15:26:43.693042737 +0100
@@ -3192,6 +3192,42 @@ determine_block_size (tree len, rtx len_
GET_MODE_MASK (GET_MODE (len_rtx)));
}
+/* Return true if STR contains the string "/gnu/store". */
+
+static bool
+store_reference_p (tree str)
+{
+ if (TREE_CODE (str) == ADDR_EXPR)
+ str = TREE_OPERAND (str, 0);
+
+ 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;
+}
+
/* Helper function to do the actual work for expand_builtin_memcpy. */
static rtx
@@ -3207,6 +3243,13 @@ expand_builtin_memcpy_args (tree dest, t
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
+ <http://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;
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