0
我做了一個如下所示的小隊列，用於存儲二進制數據。 queue_read（）和queue_del（）在隊列的一邊進行讀取和刪除操作。 queue_add（）將數據添加到隊列的另一端。當我在另一個代碼中使用此代碼存儲數據時，我正面臨分段錯誤問題。但我無法找到甚至使用gdb導致分割問題的原因。它大部分時間都像malloc-> memalign問題，但我找不到任何空指針。單獨測試這些代碼，我找不到任何問題。如果執行過程中出現任何問題，有人可能會指出這是非常棒的。由於排隊算法的分段錯誤
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct queue_node {
struct queue_node *next;
unsigned char data;
};
struct queue {
struct queue_node *first;
struct queue_node *last;
};
/* initialize the queue */
void init_queue(struct queue *q) {
q->first = q->last = NULL;
}
/* check if the queue is empty or not */
int queue_empty_p(const struct queue *q) {
return q->first == NULL;
}
/* Reading 'len' bytes data from queue to buffer variable 'value'
*
* RETURNS bytes read which can be less than or equal to the requested
* value of 'len'
*/
int queue_read(struct queue *q, unsigned char *read_buffer, unsigned int len) {
unsigned int i;
struct queue_node *tmp = (struct queue_node *) malloc(
sizeof(struct queue_node));
tmp = q->first;
for (i = 0; i < len; i++) {
if (tmp == NULL) {
read_buffer[i] = 0;
return (i);
}
read_buffer[i] = tmp->data;
tmp = tmp->next;
}
return len;
}
/* Deleting specified no of bytes from queue. Usually done after queue_read() */
int queue_del(struct queue *q, unsigned int no_of_bytes) {
unsigned int i;
for (i = 0; i < no_of_bytes; i++) {
if (!q->first) {
return 1;
}
struct queue_node *tmp = q->first;
if (q->first == q->last)
q->first = q->last = NULL;
else
q->first = q->first->next;
free(tmp);
}
return 0;
}
/* Adding 'len' bytes of data contained in the variable 'value' to the queue */
int queue_add(struct queue *q, unsigned char *value, unsigned int len) {
struct queue_node *node;
unsigned int i;
for (i = 0; i < len; i++) {
node = (struct queue_node *) malloc(sizeof(struct queue_node));
if (node == NULL) {
return 1;
}
node->data = *(value + i);
if (q->first == NULL)
q->first = q->last = node;
else {
q->last->next = node;
q->last = node;
}
node->next = NULL;
}
return 0;
}
int main() {
struct queue left_queue;
char *buffer = (char *)malloc(100);
int read_bytes;
strcpy(buffer, "This is a test");
init_queue(&left_queue);
queue_add(&left_queue, (unsigned char *) buffer, strlen(buffer));
queue_del(&left_queue, 3);
read_bytes = queue_read(&left_queue, (unsigned char *)buffer, 1500);
buffer[read_bytes]=0;
printf("Buffer: %s \nBytes read %d \n", (unsigned char *)buffer, read_bytes);
return 0;
}
編輯：的valgrind的GDB回溯輸出
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb6ef3b70 (LWP 2678)]
0x0012f4df in memalign() from /usr/lib/libefence.so.0
#0 0x0012f4df in memalign() from /usr/lib/libefence.so.0
#1 0x0012f88b in malloc() from /usr/lib/libefence.so.0
#2 0x08049576 in queue_add (q=0xb7f21fc8,
value=0xb7f2da28 "GET /wiki/Special:Search?search=rohc&sourceid=Mozilla-search HTTP/1.1\r\nHost: en.wikipedia.org\r\nUser-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.13) Gecko/20101206 Ubuntu/10.04 (lucid) Fire"...,
len=440) at pep_core.h:248
#3 0x0804cc81 in fn_process_tcp() at pep_core.c:584
#4 0x0013b96e in start_thread() from /lib/tls/i686/cmov/libpthread.so.0
#5 0x00228a4e in clone() from /lib/tls/i686/cmov/libc.so.6
#0 0x0012f4df in memalign() from /usr/lib/libefence.so.0
No symbol table info available.
#1 0x0012f88b in malloc() from /usr/lib/libefence.so.0
No symbol table info available.
#2 0x08049576 in queue_add (q=0xb7f21fc8,
value=0xb7f2da28 "GET /wiki/Special:Search?search=rohc&sourceid=Mozilla-search HTTP/1.1\r\nHost: en.wikipedia.org\r\nUser-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.13) Gecko/20101206 Ubuntu/10.04 (lucid) Fire"...,
len=440) at pep_core.h:248
node = 0xb661bff8
i = 245
#3 0x0804cc81 in fn_process_tcp() at pep_core.c:584
ip_queue_table = 0xb7f2d9fc
tmp_ip_queue_table = 0x0
tcp_conn = 0xb7f21fa8
tmp_tcp_conn = 0x0
tcphdrs = 0xb7f2da14
iphdrs = 0xb7f2da00
packet_data = 0xb7f2da28 "GET /wiki/Special:Search?search=rohc&sourceid=Mozilla-search HTTP/1.1\r\nHost: en.wikipedia.org\r\nUser-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.13) Gecko/20101206 Ubuntu/10.04 (lucid) Fire"...
read_buffer = 0xb7f17a24 ""
read_bytes = 0
payload_size = 440
ret = 0
rawfd = 9
one = 1
#4 0x0013b96e in start_thread() from /lib/tls/i686/cmov/libpthread.so.0
No symbol table info available.
#5 0x00228a4e in clone() from /lib/tls/i686/cmov/libc.so.6
No symbol table info available.
輸出
我的valgrind跑如你所說，得到了以下
Syscall param socketcall.sendto(msg) points to uninitialised byte(s)
上面的錯誤被認爲是4次，然後下面的消息
==3159== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==3159== Bad permissions for mapped region at address 0x5AD2FFC
==3159== at 0x804962F: queue_read (pep_core.h:279)
==3159== by 0x804D672: fn_thread_pep_left_sctp_client (pep_core.c:856)
==3159== by 0x403D96D: start_thread (pthread_create.c:300)
==3159== by 0x412AA4D: clone (clone.S:130)
段錯誤不一定是由空指針引起的。你說你使用gdb，你可以在segfault之後提供回溯嗎？ – Florian
你確定這個問題不是你的第二個程序嗎？我的猜測是，你將錯誤的長度傳遞給'queue_read'，它會覆蓋一些東西。就像你在你的例子中做的那樣。 –
你有沒有試過用valgrind來測試它？如果是的話，你可以給valgrind輸出。 – tune2fs