[PATCH 07/17] malloc: Add specialized dynarray for C strings

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

This patch adds an specialized dynarray to manage C strings using the
dynarray internal implementation.  It uses some private fields from
dynarray and thus it provided specific files to access and manage
the internal string buffer.

   For instance:

   struct char_array str;
   // str == "testing"
   char_array_init_str (&str, "testing");
   // c == 's'
   char c = char_array_pos (&str, 2);
   // str = "testing2"
   char_array_set_str (&str, "testing2");
   // str = "testi"
   char_array_erase (&str, 5);
   // str = "123testi"
   char_array_prepend_str (&str, "123");
   // len = 8
   size_t len = char_array_length (&str);
   // str = "123testi456"
   char_array_append_str (&str, "456");
   // str = "123testi789"
   char_array_replace_str_pos (&str, 7, "789", 3);

The provided function are not extensive and meant mainly to be use in
subsequent glob implementation cleanup.  For internal object consistency
only the function provided by char_array.c should be used, including
internal object manipulation.

To check for possible overflows in internal size manipulation a new
function, check_add_wrapv_size_t, is added on malloc-internal.  It basically
return whether the addition of two size_t overflows.

Checked on x86_64-linux-gnu.

	* malloc/Makefile (test-internal): Add tst-char_array.
	* malloc/malloc-internal (check_add_wrapv_size_t): New function.
	* malloc/char_array.c: New file.
	* malloc/tst-char-array.c: Likewise.
---
 malloc/Makefile          |   1 +
 malloc/char_array.c      | 256 +++++++++++++++++++++++++++++++++++++++++++++++
 malloc/malloc-internal.h |  14 +++
 malloc/tst-char_array.c  | 107 ++++++++++++++++++++
 4 files changed, 378 insertions(+)
 create mode 100644 malloc/char_array.c
 create mode 100644 malloc/tst-char_array.c

diff --git a/malloc/Makefile b/malloc/Makefile
index af025cb..098e3c6 100644
--- a/malloc/Makefile
+++ b/malloc/Makefile
@@ -46,6 +46,7 @@ tests-internal += \
 	 tst-dynarray \
 	 tst-dynarray-fail \
 	 tst-dynarray-at-fail \
+	 tst-char_array
 
 ifneq (no,$(have-tunables))
 tests += tst-malloc-usable-tunables
diff --git a/malloc/char_array.c b/malloc/char_array.c
new file mode 100644
index 0000000..cce9360
--- /dev/null
+++ b/malloc/char_array.c
@@ -0,0 +1,256 @@
+/* Specialized dynarray for C strings.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This file provides a dynamic C string with an initial stack allocated
+   buffer.  Since it is based on dynarray, it provided dynamic size
+   expansion and heap usage for large strings.
+
+   The following parameters are optional:
+
+   CHAR_ARRAY_INITIAL_SIZE
+      The size of the statically allocated array (default is 256).  It will
+      be used to define DYNARRAY_INITIAL_SIZE.
+
+   The following functions are provided:
+
+   bool char_array_init_empty (struct char_array *);
+   bool char_array_init_str (struct char_array *, const char *);
+   bool char_array_init_str_size (struct char_array *, const char *, size_t);
+   bool char_array_is_empty (struct char_array *);
+   const char *char_array_str (struct char_array *);
+   char char_array_pos (struct char_array *, size_t);
+   size_t char_array_length (struct char_array *);
+   bool char_array_set_str (struct char_array *, const char *);
+   bool char_array_set_str_size (struct char_array *, const char *, size_t);
+   void char_array_erase (struct char_array *, size_t);
+   bool char_array_resize_str (struct char_array *, size_t);
+   bool char_array_prepend_str (struct char_array *, const char *);
+   bool char_array_append_str (struct char_array *, const char *);
+   bool char_array_replace_str_pos (struct char_array *, size_t, const char *,
+				    size_t);
+
+   For instance:
+
+   struct char_array str;
+   // str == "testing";
+   char_array_init_str (&str, "testing");
+   // c == 's'
+   char c = char_array_pos (&str, 2);
+   // str = "testing2";
+   char_array_set_str (&str, "testing2");
+   // str = "testi";
+   char_array_erase (&str, 5);
+   // str = "123testi";
+   char_array_prepend_str (&str, "123");
+   // len = 8;
+   size_t len = char_array_length (&str);
+   // str = "123testi456";
+   char_array_append_str (&str, "456");
+   // str = "123testi789";
+   char_array_replace_str_pos (&str, 7, "789", 3);
+ */
+
+#define DYNARRAY_STRUCT            char_array
+#define DYNARRAY_ELEMENT           char
+#define DYNARRAY_PREFIX            char_array_
+#define DYNARRAY_ELEMENT_INIT(__e) (*__e = '\0')
+#ifndef CHAR_ARRAY_INITIAL_SIZE
+# define CHAR_ARRAY_INITIAL_SIZE 256
+#endif
+#define DYNARRAY_INITIAL_SIZE  CHAR_ARRAY_INITIAL_SIZE
+#include <malloc/dynarray-skeleton.c>
+#include <malloc/malloc-internal.h>
+
+/* Return a const char for the internal C string handled by 'array'.  */
+static const char * __attribute_used__
+char_array_str (struct char_array *array)
+{
+  return char_array_at (array, 0);
+}
+
+/* Return the character at position 'pos' from the char_array 'array'.  */
+static char __attribute_used__
+char_array_pos (struct char_array *array, size_t pos)
+{
+  return *char_array_at (array, pos);
+}
+
+static size_t __attribute_used__
+char_array_length (struct char_array *array)
+{
+  /* Exclude the final '\0'.  */
+  return array->dynarray_header.used - 1;
+}
+
+/* Copy the contents of string 'str' to char_array 'array', including the
+   final '\0'.  */
+static bool __attribute_used__
+char_array_set_str (struct char_array *array, const char *str)
+{
+  size_t size = strlen (str) + 1;
+  if (!char_array_resize (array, size))
+    return false;
+  memcpy (array->dynarray_header.array, str, size);
+  array->dynarray_header.used = size;
+  return true;
+}
+
+/* Copy up 'size' bytes from string 'str' to char_array 'array'.  A final
+   '\0' is appended in the char_array.  */
+static bool __attribute_used__
+char_array_set_str_size (struct char_array *array, const char *str,
+			 size_t size)
+{
+  size_t newsize;
+  if (check_add_wrapv_size_t (size, 1, &newsize)
+      || !char_array_resize (array, newsize))
+    return false;
+  *((char *) mempcpy (array->dynarray_header.array, str, size)) = '\0';
+  array->dynarray_header.used = newsize;
+  return true;
+}
+
+/* Initialize the char_array 'array' and sets it to an empty string ("").  */
+static bool __attribute_used__
+char_array_init_empty (struct char_array *array)
+{
+  char_array_init (array);
+  return char_array_set_str (array, "");
+}
+
+/* Initialize the char_array 'array' and copy the content of string 'str'.  */
+static bool __attribute_used__
+char_array_init_str (struct char_array *array, const char *str)
+{
+  char_array_init (array);
+  return char_array_set_str (array, str);
+}
+
+/* Initialize the char_array 'array' and copy the content of string 'str'
+   up to 'size' characteres.  */
+static bool __attribute_used__
+char_array_init_str_size (struct char_array *array, const char *str,
+			  size_t size)
+{
+  char_array_init (array);
+  return char_array_set_str_size (array, str, size);
+}
+
+static bool __attribute_used__
+char_array_is_empty (struct char_array *array)
+{
+  return *char_array_at (array, 0) == '\0';
+}
+
+/* Remove the byte at position 'pos' from char_array 'array'.  The contents
+   are moved internally if the position is not at the end of the internal
+   buffer.  */
+static bool __attribute_used__
+char_array_erase (struct char_array *array, size_t pos)
+{
+  if (pos >= array->dynarray_header.used - 1)
+    return false;
+
+  char *ppos = char_array_at (array, pos);
+  char *lpos = array->dynarray_header.array + array->dynarray_header.used;
+  ptrdiff_t size = lpos - ppos;
+  memmove (ppos, ppos + 1, size);
+  array->dynarray_header.used--;
+  return true;
+}
+
+/* Resize the char_array 'array' to size 'count' maintaining the ending
+   '\0' byte.  */
+static bool __attribute_used__
+char_array_crop (struct char_array *array, size_t size)
+{
+  if (size >= (array->dynarray_header.used - 1)
+      || !char_array_resize (array, size + 1))
+    return false;
+
+  array->dynarray_header.array[array->dynarray_header.used] = '\0';
+  return true;
+}
+
+/* Prepend the contents of string 'str' to char_array 'array', including the
+   final '\0' byte.  */
+static bool __attribute_used__
+char_array_prepend_str (struct char_array *array, const char *str)
+{
+  size_t size = strlen (str);
+  /* Resizing the array might change its used elements and we need below
+     to correct copy the elements.  */
+  size_t used = array->dynarray_header.used;
+
+  size_t newsize;
+  if (check_add_wrapv_size_t (used, size, &newsize)
+      || !char_array_resize (array, newsize))
+    return false;
+
+  /* Make room for the string and copy it.  */
+  memmove (array->dynarray_header.array + size, array->dynarray_header.array,
+           used);
+  memcpy (array->dynarray_header.array, str, size);
+  array->dynarray_header.used = newsize;
+  return true;
+}
+
+/* Append the contents of string 'str' to char_array 'array, including the
+   final '\0' byte.  */
+static bool __attribute_used__
+char_array_append_str (struct char_array *array, const char *str)
+{
+  size_t size = strlen (str);
+  /* Resizing the array might change its used elements and it used it below
+     to correct copy the elements.  */
+  size_t used = array->dynarray_header.used - 1;
+
+  /* array 'used' does account for final '\0', so there is no need to add
+     an extra element to calculate the final required size.  */
+  size_t newsize;
+  if (check_add_wrapv_size_t (used + 1, size, &newsize)
+      || !char_array_resize (array, newsize))
+    return false;
+
+  /* Start to append at '\0' up to string length and add a final '\0'.  */
+  *(char*) mempcpy (array->dynarray_header.array + used, str, size) = '\0';
+  array->dynarray_header.used = newsize;
+  return true;
+}
+
+/* Replace the contents starting of position 'pos' of char_array 'array'
+   with the contents of string 'str' up to 'len' bytes.  A final '\0'
+   is appended in the string.  */
+static bool __attribute_used__
+char_array_replace_str_pos (struct char_array *array, size_t pos,
+                            const char *str, size_t len)
+{
+  if (pos > array->dynarray_header.used)
+    return false;
+
+  size_t newsize;
+  if (check_add_wrapv_size_t (pos, len, &newsize)
+      || check_add_wrapv_size_t (newsize, 1, &newsize)
+      || !char_array_resize (array, newsize))
+    return false;
+
+  char *start = char_array_at (array, pos);
+  *(char *) mempcpy (start, str, len) = '\0';
+  array->dynarray_header.used = newsize;
+  return true;
+}
diff --git a/malloc/malloc-internal.h b/malloc/malloc-internal.h
index dbd801a..3066cd3 100644
--- a/malloc/malloc-internal.h
+++ b/malloc/malloc-internal.h
@@ -101,4 +101,18 @@ check_mul_overflow_size_t (size_t left, size_t right, size_t *result)
 #endif
 }
 
+/* Set *R = A + B.  Return true if the answer is mathematically incorrect due
+   to overflow; in this case, *R is the low order bits of the correct
+   answer.  */
+static inline bool
+check_add_wrapv_size_t (size_t a, size_t b, size_t *r)
+{
+#if 5 <= __GNUC__
+  return __builtin_add_overflow (a, b, r);
+#else
+  *r = a + b;
+  return *r < a;
+#endif
+}
+
 #endif /* _MALLOC_INTERNAL_H */
diff --git a/malloc/tst-char_array.c b/malloc/tst-char_array.c
new file mode 100644
index 0000000..53f9482
--- /dev/null
+++ b/malloc/tst-char_array.c
@@ -0,0 +1,107 @@
+/* Test for char_array.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <string.h>
+
+#include <malloc/char_array.c>
+
+#include <malloc.h>
+#include <mcheck.h>
+#include <stdint.h>
+#include <support/check.h>
+#include <support/support.h>
+
+static int
+do_test (void)
+{
+  mtrace ();
+
+  {
+    struct char_array str;
+    TEST_VERIFY_EXIT (char_array_init_empty (&str) == true);
+    TEST_VERIFY_EXIT (char_array_length (&str) == 0);
+    TEST_VERIFY_EXIT (char_array_is_empty (&str) == true);
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "") == 0);
+    char_array_free (&str);
+  }
+
+  {
+    struct char_array str;
+    TEST_VERIFY_EXIT (char_array_init_str (&str, "testing"));
+    TEST_VERIFY_EXIT (char_array_length (&str) == strlen ("testing"));
+    TEST_VERIFY_EXIT (char_array_pos (&str, 2) == 's');
+    TEST_VERIFY_EXIT (char_array_is_empty (&str) == false);
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "testing") == 0);
+    char_array_free (&str);
+  }
+
+  {
+    struct char_array str;
+    TEST_VERIFY_EXIT (char_array_init_str_size (&str, "testing", 4));
+    TEST_VERIFY_EXIT (char_array_length (&str) == 4);
+    TEST_VERIFY_EXIT (char_array_pos (&str, 2) == 's');
+    TEST_VERIFY_EXIT (char_array_is_empty (&str) == false);
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "test") == 0);
+    char_array_free (&str);
+  }
+
+  {
+    struct char_array str;
+    TEST_VERIFY_EXIT (char_array_init_str (&str, "testing"));
+    TEST_VERIFY_EXIT (char_array_set_str (&str, "abcdef"));
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "abcdef") == 0);
+    TEST_VERIFY_EXIT (char_array_set_str_size (&str, "abcdef", 4));
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "abcd") == 0);
+    char_array_free (&str);
+  }
+
+  {
+    struct char_array str;
+    TEST_VERIFY_EXIT (char_array_init_str (&str, "testing"));
+    TEST_VERIFY_EXIT (char_array_erase (&str, 4) == true);
+    TEST_VERIFY_EXIT (char_array_length (&str) == strlen ("testing") - 1);
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "testng") == 0);
+    TEST_VERIFY_EXIT (char_array_erase (&str, char_array_length (&str))
+		      == false);
+    TEST_VERIFY_EXIT (char_array_length (&str) == strlen ("testing") - 1);
+    TEST_VERIFY_EXIT (char_array_erase (&str, char_array_length (&str) - 1)
+		      == true);
+    TEST_VERIFY_EXIT (char_array_length (&str) == strlen ("testing") - 2);
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "testn") == 0);
+    char_array_free (&str);
+  }
+
+  {
+    struct char_array str;
+    TEST_VERIFY_EXIT (char_array_init_str (&str, "test"));
+    TEST_VERIFY_EXIT (char_array_prepend_str (&str, "123"));
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "123test") == 0);
+    TEST_VERIFY_EXIT (char_array_length (&str) == strlen ("123test"));
+    TEST_VERIFY_EXIT (char_array_append_str (&str, "456"));
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "123test456") == 0);
+    TEST_VERIFY_EXIT (char_array_length (&str) == strlen ("123test456"));
+    TEST_VERIFY_EXIT (char_array_replace_str_pos (&str, 7, "789", 3));
+    TEST_VERIFY_EXIT (strcmp (char_array_str (&str), "123test789") == 0);
+    TEST_VERIFY_EXIT (char_array_length (&str) == strlen ("123test789"));
+    char_array_free (&str);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.7.4