理解 malloc.h 差异：__attribute_malloc__

Question

有人可以帮我找到在哪里或解释什么__attribute_malloc__意思吗？并且__wur？

我正在使用一些大约 120 个 fortran f77 文件的旧代码，但使用了一些 C 文件，其中它只使用malloc()并且它们确实使用# include <malloc.h>.

我已经 kdiff'dstdlib.h和malloc.h; 不太确定我能找到这两种实现之间的区别吗？

正在使用的 Linux 发行版可以对 的内容负责吗/usr/include/malloc.h？我正在使用具有 GCC 4.3.4 的 SLES 11.4 x86-64，这里是/usr/include/malloc.h：

/* Prototypes and definition for malloc implementation.
   Copyright (C) 1996, 1997, 1999, 2000, 2002-2004, 2005, 2007, 2009
   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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#ifndef _MALLOC_H
#define _MALLOC_H 1

#include <features.h>
#include <stddef.h>
#include <stdio.h>

# define __malloc_ptr_t  void *

/* Used by GNU libc internals. */
#define __malloc_size_t size_t
#define __malloc_ptrdiff_t ptrdiff_t

#ifdef __GNUC__

# define __MALLOC_P(args)   args __THROW
/* This macro will be used for functions which might take C++ callback functions.  */
# define __MALLOC_PMT(args) args

#else   /* Not GCC.  */

# define __MALLOC_P(args)   args
# define __MALLOC_PMT(args) args

#endif  /* GCC.  */


__BEGIN_DECLS

/* Allocate SIZE bytes of memory.  */
extern void *malloc __MALLOC_P ((size_t __size)) __attribute_malloc__ __wur;

/* Allocate NMEMB elements of SIZE bytes each, all initialized to 0.  */
extern void *calloc __MALLOC_P ((size_t __nmemb, size_t __size)) __attribute_malloc__ __wur;

/* Re-allocate the previously allocated block in __ptr, making the new block SIZE bytes long.  */
/* __attribute_malloc__ is not used, because if realloc returns
   the same pointer that was passed to it, aliasing needs to be allowed
   between objects pointed by the old and new pointers.  */
extern void *realloc __MALLOC_P ((void *__ptr, size_t __size)) __attribute_warn_unused_result__;

/* Free a block allocated by `malloc', `realloc' or `calloc'.  */
extern void free __MALLOC_P ((void *__ptr));

/* Free a block allocated by `calloc'. */
extern void cfree __MALLOC_P ((void *__ptr));

/* Allocate SIZE bytes allocated to ALIGNMENT bytes.  */
extern void *memalign __MALLOC_P ((size_t __alignment, size_t __size)) __attribute_malloc__ __wur;

/* Allocate SIZE bytes on a page boundary.  */
extern void *valloc __MALLOC_P ((size_t __size)) __attribute_malloc__ __wur;

/* Equivalent to valloc(minimum-page-that-holds(n)), that is, round up __size to nearest pagesize. */
extern void * pvalloc __MALLOC_P ((size_t __size)) __attribute_malloc__ __wur;

/* Underlying allocation function; successive calls should return contiguous pieces of memory.  */
extern void *(*__morecore) __MALLOC_PMT ((ptrdiff_t __size));

/* Default value of `__morecore'.  */
extern void *__default_morecore __MALLOC_P ((ptrdiff_t __size)) __attribute_malloc__;

/* SVID2/XPG mallinfo structure */

struct mallinfo {
  int arena;    /* non-mmapped space allocated from system */
  int ordblks;  /* number of free chunks */
  int smblks;   /* number of fastbin blocks */
  int hblks;    /* number of mmapped regions */
  int hblkhd;   /* space in mmapped regions */
  int usmblks;  /* maximum total allocated space */
  int fsmblks;  /* space available in freed fastbin blocks */
  int uordblks; /* total allocated space */
  int fordblks; /* total free space */
  int keepcost; /* top-most, releasable (via malloc_trim) space */
};

/* Returns a copy of the updated current mallinfo. */
extern struct mallinfo mallinfo __MALLOC_P ((void));

/* SVID2/XPG mallopt options */
#ifndef M_MXFAST
# define M_MXFAST  1    /* maximum request size for "fastbins" */
#endif
#ifndef M_NLBLKS
# define M_NLBLKS  2    /* UNUSED in this malloc */
#endif
#ifndef M_GRAIN
# define M_GRAIN   3    /* UNUSED in this malloc */
#endif
#ifndef M_KEEP
# define M_KEEP    4    /* UNUSED in this malloc */
#endif

/* mallopt options that actually do something */
#define M_TRIM_THRESHOLD    -1
#define M_TOP_PAD           -2
#define M_MMAP_THRESHOLD    -3
#define M_MMAP_MAX          -4
#define M_CHECK_ACTION      -5
#define M_PERTURB       -6
#define M_ARENA_TEST        -7
#define M_ARENA_MAX     -8

/* General SVID/XPG interface to tunable parameters. */
extern int mallopt __MALLOC_P ((int __param, int __val));

/* Release all but __pad bytes of freed top-most memory back to the
   system. Return 1 if successful, else 0. */
extern int malloc_trim __MALLOC_P ((size_t __pad));

/* Report the number of usable allocated bytes associated with allocated chunk __ptr. */
extern size_t malloc_usable_size __MALLOC_P ((void *__ptr));

/* Prints brief summary statistics on stderr. */
extern void malloc_stats __MALLOC_P ((void));

/* Output information about state of allocator to stream FP.  */
extern int malloc_info (int __options, FILE *__fp);

/* Record the state of all malloc variables in an opaque data structure. */
extern void *malloc_get_state __MALLOC_P ((void));

/* Restore the state of all malloc variables from data obtained with malloc_get_state(). */
extern int malloc_set_state __MALLOC_P ((void *__ptr));

/* Called once when malloc is initialized; redefining this variable in
   the application provides the preferred way to set up the hook pointers. */
extern void (*__malloc_initialize_hook) __MALLOC_PMT ((void));

/* Hooks for debugging and user-defined versions. */
extern void (*__free_hook) __MALLOC_PMT ((void *__ptr, __const __malloc_ptr_t));
extern void *(*__malloc_hook) __MALLOC_PMT ((size_t __size, __const __malloc_ptr_t));
extern void *(*__realloc_hook) __MALLOC_PMT ((void *__ptr, size_t __size, __const __malloc_ptr_t));
extern void *(*__memalign_hook) __MALLOC_PMT ((size_t __alignment, size_t __size, __const __malloc_ptr_t));
extern void (*__after_morecore_hook) __MALLOC_PMT ((void));

/* Activate a standard set of debugging hooks. */
extern void __malloc_check_init __MALLOC_P ((void));


__END_DECLS

#endif /* malloc.h */

Answer 1

如果您的代码仅使用标准内存分配接口（malloc、realloc、calloc和free），那么您应该包含stdlib.h，而不应该包含malloc.h。 malloc.h是一个非标准标头，存在的原因有两个：向后兼容某些 1980 年代、标准化前的 C 库，以及作为声明一系列接口扩展的地方malloc，这样它们就不会污染命名空间没有使用它们。 stdlib.h是获取内存分配函数的标准位置。它还声明了一堆与内存分配无关的其他内容。比较 和 之间的差异malloc.h不会stdlib.h告诉你任何有用的信息。

您不需要关心 or __attribute_malloc__（__wur或__THROW，或者一般来说，C 库头中的任何内容都没有记录，并且其名称以两个下划线开头）的含义。它们是 C 库用来与 C 编译器就“不是你的问题”的事情进行通信的注释。mallocin的声明malloc.h应该与mallocin的声明完全相同stdlib.h，包括任何注释；如果不是，则这是 C 库中的错误。由于这是 GNU C 库，您正在查看其标头，因此我通常会告诉您在https://sourceware.org/bugzilla/提交错误报告，但malloc.h您引用的内容比当前开发系列早十年，我刚刚检查过，它们在当前的开发系列中是相同的，所以如果有差异，那是因为你的 Linux 发行版已经过时了，你应该与他们一起解决这个问题，而不是与 GNU libc 上游一起解决。

不过，为了满足您的好奇心，我将告诉您这些注释的含义。__attribute_malloc__和__wur是定义的宏（由 GNU libc 中的每个sys/cdefs.h公共标头间接包含）。 展开为、展开为或 展开为空，具体取决于 的值。__attribute_malloc____attribute__ ((__malloc__))__wur__attribute__ ((__warn_unused_result__))_FORTIFY_SOURCE

这两种__attribute__ ((...))结构都记录在GCC 手册中。该malloc属性告诉编译器这是一个“类似于 malloc”的函数，即函数返回的指针 P 不能为函数返回时任何其他有效的指针别名，而且在任何寻址的存储中都不会出现指向有效对象的指针by P”，这对优化器有一些帮助。（当前版本的 GCC 已经知道这一点malloc，即使它是在没有该注释的情况下声明的，但旧版本却没有。）该warn_unused_result属性“如果具有此属性的函数的调用者不使用其返回值，则会发出警告” ”，这作为 的安全功能是有意义的malloc，因为如果您调用malloc但不使用其返回值，则会出现内存泄漏。