Question

我目前正在开发一个内存分配器，我现在已经提供了这个代码，但是当我执行LD_PRELOAD时，几乎所有命令都会出现以下代码。

Forall field In form.Fields     
    fieldCount = fieldCount + 1
    msgString = msgString & Chr(10) &   "     " & field

    If (field  Like "*Act*")  Then          
        ActfieldCount = ActfieldCount + 1

        If (field  Like "RNomAct1")  Then
            Msgbox("RNomAct1 found in SourceString!")
'thoses do not work             

'               test = field.GetItemValue("RNomAct1")   
'               test = field.FieldGetText("RNomAct1")   
'               Messagebox( test( 0 ) )

        End If
    Else
        Msgbox("Could not find the SearchString.")
    End If

End Forall

这是malloc.h：

#include <pthread.h>
#include "malloc.h"

t_mem_map       g_map;
int         g_empty_map = TRUE;

static t_ctrl       *get_free_block(size_t size)
{
  t_ctrl        *tmp;

  tmp = g_map.head;
  while (tmp != NULL)
    {
      if (tmp->is_free == TRUE && tmp->size < size)
    {
      tmp->is_free = FALSE;
      return (tmp);
    }
      tmp = tmp->next;
    }
  return (NULL);
}

static void     *init_map(size_t size)
{
  t_ctrl        *tmp;

  g_map.map_size = DEFAULT_MAP_SIZE;
  while (g_map.map_size < size + sizeof(t_ctrl))
    g_map.map_size += DEFAULT_MAP_SIZE;
  if ((g_map.head = (t_ctrl *)sbrk(g_map.map_size)) == (void *)-1)
    return (NULL);
  tmp = g_map.head;
  tmp->next = NULL;
  tmp->prev = NULL;
  tmp->size = size;
  tmp->is_free = FALSE;
  g_map.free_space = g_map.map_size - size - sizeof(t_ctrl);
  g_empty_map = FALSE;
  unlock_thread();
  return ((void *)((char *)tmp + sizeof(t_ctrl)));
}

static void     *add_block(size_t size)
{
  t_ctrl        *tmp;
  t_ctrl        *new;

  tmp = get_free_block(size);
  if (tmp != NULL)
    return ((void *)((char *)tmp + sizeof(t_ctrl)));
  tmp = g_map.head;
  while (tmp->next != NULL)
    tmp = tmp->next;
  new = (t_ctrl *)((char *)tmp + sizeof(t_ctrl) + tmp->size);
  new->prev = tmp;
  new->next = NULL;
  tmp->next = new;
  new->size = size;
  new->is_free = FALSE;
  g_map.free_space -= (new->size + sizeof(t_ctrl));
  unlock_thread();
  return ((void *)((char *)new + sizeof(t_ctrl)));
}

static void     *resize_map(size_t size)
{
  size_t        size_shift;

  size_shift = 0;
  while (g_map.free_space < size + sizeof(t_ctrl))
    {
      g_map.map_size += DEFAULT_MAP_SIZE;
      g_map.free_space += DEFAULT_MAP_SIZE;
      size_shift += DEFAULT_MAP_SIZE;
    }
  if (sbrk(size_shift) == (void *)-1)
    return (NULL);
  return (add_block(size));
}

void            *malloc(size_t size)
{
  size_t        a_size;

  lock_thread();
  a_size = ALIGN(size);
  if (g_empty_map == TRUE)
    return (init_map(a_size));
  else
    {
      if ((a_size + sizeof(t_ctrl)) <= g_map.free_space)
        return (add_block(a_size));
      else
    return (resize_map(a_size));
    }
  return (NULL);
}

通过一些研究，我发现segfault可能来自get_free_block（）函数中的while循环，但我无法理解为什么。

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

# define TRUE 0
# define FALSE 1

# define SUCCESS 0
# define FAILURE 1


# ifndef __X86_64__
#  define ALIGNMENT (16)
# else
#  define ALIGNMENT (8)
# endif

# define ALIGN(size) (((size) + (ALIGNMENT - 1)) &~ (ALIGNMENT - 1))
# define DEFAULT_MAP_SIZE (ALIGN(sysconf(_SC_PAGESIZE)))

typedef struct      s_ctrl
{
  size_t        is_free;
  size_t        size;
  struct s_ctrl     *next;
  struct s_ctrl     *prev;
}           t_ctrl;

typedef struct      s_mem_map
{
  size_t        map_size;
  size_t        free_space;
  //  int           free_blocks;
  //int         nb_blocks;
  t_ctrl        *head;
}           t_mem_map;

Answer 1

无法验证这是唯一的问题，但您正在检查tmp->size < size，而您可能应该检查tmp->size >= size。

内存分配器实现段错误

1 个答案: