Re: alloc_size attribute

[Bruno Haible]

Jim Meyering wrote:
> ---------------------------------------------
> While looking through gcc's documentation (latest upstream),
> I noticed this, which can be put to good use in xalloc.h:
> 
>     @item alloc_size
>     @cindex @code{alloc_size} attribute
>     The @code{alloc_size} attribute is used to tell the compiler that the
>     function return value points to memory, where the size is given by
>     one or two of the functions parameters.  GCC uses this
>     information to improve the correctness of @code{__builtin_object_size}.

Here is a proposed patch:


2010-10-17  Bruno Haible  <address@hidden>

        Make use of GCC's attribute __alloc_size__.
        * lib/xalloc.h (ATTRIBUTE_ALLOC_SIZE): New macro.
        (xmalloc, xzalloc, xcalloc, xrealloc, xmemdup, xnmalloc, xnrealloc,
        xcharalloc): Declare with ATTRIBUTE_ALLOC_SIZE.
        * lib/eealloc.h (eemalloc, eerealloc): Declare with attribute
        __alloc_size__.
        * lib/pagealign_alloc.h (pagealign_alloc, pagealign_xalloc): Likewise.
        Suggested by Jim Meyering.

--- lib/eealloc.h.orig  Sun Oct 17 15:33:30 2010
+++ lib/eealloc.h       Sun Oct 17 15:33:29 2010
@@ -1,5 +1,5 @@
 /* Memory allocation with expensive empty allocations.
-   Copyright (C) 2003, 2008, 2009, 2010 Free Software Foundation, Inc.
+   Copyright (C) 2003, 2008, 2010 Free Software Foundation, Inc.
    Written by Bruno Haible <address@hidden>, 2003,
    based on prior work by Jim Meyering.
 
@@ -35,7 +35,12 @@
 # define eemalloc malloc
 #else
 # if __GNUC__ >= 3
-static inline void *eemalloc (size_t n) __attribute__ ((__malloc__));
+static inline void *eemalloc (size_t n)
+     __attribute__ ((__malloc__))
+#  if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+     __attribute__ ((__alloc_size__ (1)))
+#  endif
+  ;
 # endif
 static inline void *
 eemalloc (size_t n)
@@ -50,6 +55,10 @@
 #if REALLOC_0_IS_NONNULL
 # define eerealloc realloc
 #else
+# if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+static inline void *eerealloc (void *p, size_t n)
+     __attribute__ ((__alloc_size__ (2)));
+# endif
 static inline void *
 eerealloc (void *p, size_t n)
 {
--- lib/pagealign_alloc.h.orig  Sun Oct 17 15:33:30 2010
+++ lib/pagealign_alloc.h       Sun Oct 17 15:27:53 2010
@@ -1,6 +1,6 @@
 /* Memory allocation aligned to system page boundaries.
 
-   Copyright (C) 2005, 2008, 2009, 2010 Free Software Foundation, Inc.
+   Copyright (C) 2005, 2008, 2010 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -29,6 +29,9 @@
 extern void *pagealign_alloc (size_t size)
 # if __GNUC__ >= 3
      __attribute__ ((__malloc__))
+#  if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+     __attribute__ ((__alloc_size__ (1)))
+#  endif
 # endif
      ;
 
@@ -37,6 +40,9 @@
 extern void *pagealign_xalloc (size_t size)
 # if __GNUC__ >= 3
      __attribute__ ((__malloc__))
+#  if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+     __attribute__ ((__alloc_size__ (1)))
+#  endif
 # endif
      ;
 
--- lib/xalloc.h.orig   Sun Oct 17 15:33:30 2010
+++ lib/xalloc.h        Sun Oct 17 15:32:00 2010
@@ -46,6 +46,14 @@
 #  endif
 # endif
 
+# ifndef ATTRIBUTE_ALLOC_SIZE
+#  if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+#   define ATTRIBUTE_ALLOC_SIZE(args) __attribute__ ((__alloc_size__ args))
+#  else
+#   define ATTRIBUTE_ALLOC_SIZE(args)
+#  endif
+# endif
+
 /* This function is always triggered when memory is exhausted.
    It must be defined by the application, either explicitly
    or by using gnulib's xalloc-die module.  This is the
@@ -53,13 +61,19 @@
    memory allocation failure.  */
 extern void xalloc_die (void) ATTRIBUTE_NORETURN;
 
-void *xmalloc (size_t s) ATTRIBUTE_MALLOC;
-void *xzalloc (size_t s) ATTRIBUTE_MALLOC;
-void *xcalloc (size_t n, size_t s) ATTRIBUTE_MALLOC;
-void *xrealloc (void *p, size_t s);
+void *xmalloc (size_t s)
+      ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((1));
+void *xzalloc (size_t s)
+      ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((1));
+void *xcalloc (size_t n, size_t s)
+      ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((1, 2));
+void *xrealloc (void *p, size_t s)
+      ATTRIBUTE_ALLOC_SIZE ((2));
 void *x2realloc (void *p, size_t *pn);
-void *xmemdup (void const *p, size_t s) ATTRIBUTE_MALLOC;
-char *xstrdup (char const *str) ATTRIBUTE_MALLOC;
+void *xmemdup (void const *p, size_t s)
+      ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((2));
+char *xstrdup (char const *str)
+      ATTRIBUTE_MALLOC;
 
 /* Return 1 if an array of N objects, each of size S, cannot exist due
    to size arithmetic overflow.  S must be positive and N must be
@@ -106,10 +120,13 @@
 # if HAVE_INLINE
 #  define static_inline static inline
 # else
-void *xnmalloc (size_t n, size_t s) ATTRIBUTE_MALLOC;
-void *xnrealloc (void *p, size_t n, size_t s);
+void *xnmalloc (size_t n, size_t s)
+      ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((1, 2));
+void *xnrealloc (void *p, size_t n, size_t s)
+      ATTRIBUTE_ALLOC_SIZE ((2, 3));
 void *x2nrealloc (void *p, size_t *pn, size_t s);
-char *xcharalloc (size_t n) ATTRIBUTE_MALLOC;
+char *xcharalloc (size_t n)
+      ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((1));
 # endif
 
 # ifdef static_inline
@@ -117,7 +134,8 @@
 /* Allocate an array of N objects, each with S bytes of memory,
    dynamically, with error checking.  S must be nonzero.  */
 
-static_inline void *xnmalloc (size_t n, size_t s) ATTRIBUTE_MALLOC;
+static_inline void *xnmalloc (size_t n, size_t s)
+                    ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((1, 2));
 static_inline void *
 xnmalloc (size_t n, size_t s)
 {
@@ -129,6 +147,8 @@
 /* Change the size of an allocated block of memory P to an array of N
    objects each of S bytes, with error checking.  S must be nonzero.  */
 
+static_inline void *xnrealloc (void *p, size_t n, size_t s)
+                    ATTRIBUTE_ALLOC_SIZE ((2, 3));
 static_inline void *
 xnrealloc (void *p, size_t n, size_t s)
 {
@@ -229,7 +249,8 @@
 /* Return a pointer to a new buffer of N bytes.  This is like xmalloc,
    except it returns char *.  */
 
-static_inline char *xcharalloc (size_t n) ATTRIBUTE_MALLOC;
+static_inline char *xcharalloc (size_t n)
+                    ATTRIBUTE_MALLOC ATTRIBUTE_ALLOC_SIZE ((1));
 static_inline char *
 xcharalloc (size_t n)
 {