我使用malloc初始化了一个全局变量page_table，如下所示。里面的每个元素都是一个结构：
page* page_table;
void init_clock(FILE* fd,int num_of_frames){
total_frames = num_of_frames;
fp = fd;
page_table = malloc(sizeof(page)*num_of_frames);
int i;
for(i=0;i<num_of_frames;i++){
page_table[i].page_number = -1;
page_table[i].dirty = 0;
page_table[i].valid = 0;
page_table[i].referenced = 0;
page_table[i].virtual_time = -1;
}
}
在我的另一种方法中，每次它都会生成一个页面结构。如果它已经在页面表中，它将被更新。如果它不在页面表中，但是有可用空间，则会添加它。否则，从页面表中逐出页面。
void execute_clock(){
int available_frames = total_frames;
int next = 0; // next location in the page table
int page_to_examine = 0; // next page that will be evicted
unsigned int address;
char mode;
while(fscanf(fp,"%x %c", &address, &mode) != EOF){
printf("%08x,%c\n",address,mode);
page new_access = {address>>12,1,mode=='W',1,mem_access};
/* add the frame into the frame array */
int location_in_table = already_in_table(new_access);
if( location_in_table != -1){ // if page is already in table, update stats
page_table[location_in_table].referenced = 1;
if(new_access.dirty) page_table[location_in_table].dirty = 1;
// printf("hit\n");
}
else if(available_frames){ // if there are spaces available, add directly
page_table[next] = new_access;
available_frames--;
next = (next+1)%total_frames;
page_faults++;
// printf("page fault - no eviction\n");
}
else{ // evict page out of table
/* find the page to evict */
int found = 0;
while(!found){
if (page_table[page_to_examine].referenced == 0){
found = 1;
}
else page_table[page_to_examine].referenced = 0;
page_to_examine = (page_to_examine+1)%total_frames;
}
/* evict the page */
int evict = page_to_examine == 0?total_frames-1:page_to_examine-1;
if(page_table[evict].dirty == 1){
disk_writes++;
printf("evict dirty %08x\n",page_table[evict].page_number);
}else{
printf("evict clean %08x\n",page_table[evict].page_number);
}
page_table[page_to_examine-1] = new_access;
page_faults++;
}
mem_access++;
print_table();
}
}
我的问题是在运行上面的代码之后，当我尝试使用以下内容释放内存：
void exit_clock(){
free(page_table);
}
该程序刚刚停止运行。错误是：
*** glibc detected *** ./main: free(): invalid next size (normal): 0x00000000006 02010 ***
======= Backtrace: =========
/lib64/libc.so.6[0x34ff676166]
/lib64/libc.so.6[0x34ff678ca3]
/lib64/libc.so.6(fclose+0x14d)[0x34ff6667cd]
./main[0x400d7a]
./main[0x40075f]
/lib64/libc.so.6(__libc_start_main+0xfd)[0x34ff61ed1d]
./main[0x400629]
======= Memory map: ========
00400000-00402000 r-xp 00000000 00:1a 2136211636 /afs/pi tt.edu/home/z/i/ziz19/private/cs1550/project3/main
00601000-00602000 rw-p 00001000 00:1a 2136211636 /afs/pi tt.edu/home/z/i/ziz19/private/cs1550/project3/main
00602000-00623000 rw-p 00000000 00:00 0 [heap]
34fee00000-34fee20000 r-xp 00000000 fd:00 127 /lib64/ ld-2.12.so
34ff01f000-34ff020000 r--p 0001f000 fd:00 127 /lib64/ ld-2.12.so
34ff020000-34ff021000 rw-p 00020000 fd:00 127 /lib64/ ld-2.12.so
34ff021000-34ff022000 rw-p 00000000 00:00 0
34ff600000-34ff78b000 r-xp 00000000 fd:00 131 /lib64/ libc-2.12.so
34ff78b000-34ff98a000 ---p 0018b000 fd:00 131 /lib64/ libc-2.12.so
34ff98a000-34ff98e000 r--p 0018a000 fd:00 131 /lib64/ libc-2.12.so
34ff98e000-34ff98f000 rw-p 0018e000 fd:00 131 /lib64/ libc-2.12.so
34ff98f000-34ff994000 rw-p 00000000 00:00 0
3505a00000-3505a16000 r-xp 00000000 fd:00 609 /lib64/ libgcc_s-4.4.7-20120601.so.1
3505a16000-3505c15000 ---p 00016000 fd:00 609 /lib64/ libgcc_s-4.4.7-20120601.so.1
3505c15000-3505c16000 rw-p 00015000 fd:00 609 /lib64/ libgcc_s-4.4.7-20120601.so.1
7ffff7fd3000-7ffff7fd6000 rw-p 00000000 00:00 0
7ffff7ffb000-7ffff7ffe000 rw-p 00000000 00:00 0
7ffff7ffe000-7ffff7fff000 r-xp 00000000 00:00 0 [vdso]
7ffffffea000-7ffffffff000 rw-p 00000000 00:00 0 [stack]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsysca ll]
Aborted (core dumped)
我不确定为什么会出现这个问题。我只在execute_clock方法中将本地页面结构分配给page_table。甚至局部变量都被破坏了，这不应该影响我免费的malloc内存。
我发现了这个问题。这是圆形数组的索引，我没有正确更新。