Valgrind说"memcpy中的源和目标重叠"关于两个缓冲区,但它们似乎没有重叠

Question

最后编辑在OP结束

我用Valgrind测试了一个项目中使用的函数,它说"memcpy中的源和目标重叠",并且还给出了"无效读取"和"无效写入"错误.我修复了代码,以便不重叠这两个缓冲区但没有结果.这是代码:

static
int download_build_buffer(char **seq_numbered_buffer, int seq_n, int dim_payload, char *buffer) {

if(!seq_numbered_buffer)
    return 1;

/* allocates seq_numbered_buffer */
if(*seq_numbered_buffer != NULL) {
    free(*seq_numbered_buffer);
    *seq_numbered_buffer = NULL;
}
if(!(*seq_numbered_buffer = malloc((SIZE_SEQ_N + SIZE_DIM_S + dim_payload + 1) * sizeof(char))))
    return 1;

#if DEBUG_DOWNLOAD
fprintf(stderr, "download_build_buffer %d: seq->%d, dim->%d\n",
                getpid(), seq_n, dim_payload);
#endif

/* prints sequence number in its string */
seq_n = htonl(seq_n);
if(!memcpy(*seq_numbered_buffer, &seq_n, SIZE_SEQ_N))
    return 1;
dim_payload = htonl(dim_payload);
if(!memcpy(&(*seq_numbered_buffer)[SIZE_SEQ_N], &dim_payload, SIZE_DIM_S))
    return 1;

/* creates payload -> buffer = seq_number + buffer */
if(!memcpy(&(*seq_numbered_buffer)[SIZE_SEQ_N+SIZE_DIM_S], buffer, dim_payload))
    return 1;
(*seq_numbered_buffer)[SIZE_SEQ_N+SIZE_DIM_S+dim_payload] = 0;

return 0;
}

正在使用以下函数调用此函数:

/* allocates buffer */
if(buffer != NULL) {
    free(buffer);
    buffer = NULL;
}
assert((buffer = malloc((dim_payload+1)*sizeof(char)))
               != NULL);

/* stores bytes in buffer */
if((n = read(fd, buffer, dim_payload)) <= 0)
    break;
buffer[n] = 0;
buf_len = n;

/* increments seq_number */
seq_n = next_request;

/* creates payload -> buffer = seq_number + buffer */
if(download_build_buffer(&seq_numbered_buffer, seq_n, dim_payload, buffer))
    return 1;

其中seq_numbered缓冲区和缓冲区被定义并初始化为:

char *seq_numbered_buffer = NULL,
     *buffer = NULL;

另外,我试图用memmove替换memcpy但没有结果:(我的Valgrind输出是

==3921== Source and destination overlap in memcpy(0x41bb2b0, 0x41bb070, 131072)
==3921==    at 0x4027BD6: memcpy (mc_replace_strmem.c:635)
==3921==    by 0x8049A8D: download_build_buffer (uftp_server.c:791)
==3921==    by 0x8049F4C: server_download_file (uftp_server.c:989)
==3921==    by 0x804A4E1: data_connection_proc (uftp_server.c:1209)    
==3921==    by 0x804AEE8: main (uftp_server.c:1512)
==3921== 
==3921== Invalid read of size 4
==3921==    at 0x4027D42: memcpy (mc_replace_strmem.c:635)
==3921==    by 0x8049A8D: download_build_buffer (uftp_server.c:791)
==3921==    by 0x8049F4C: server_download_file (uftp_server.c:989)
==3921==    by 0x804A4E1: data_connection_proc (uftp_server.c:1209)
==3921==    by 0x804AEE8: main (uftp_server.c:1512)
==3921==  Address 0x41db06c is not stack'd, malloc'd or (recently) free'd
==3921== 
==3921== Invalid write of size 4
==3921==    at 0x4027D44: memcpy (mc_replace_strmem.c:635)
==3921==    by 0x8049A8D: download_build_buffer (uftp_server.c:791)
==3921==    by 0x8049F4C: server_download_file (uftp_server.c:989)
==3921==    by 0x804A4E1: data_connection_proc (uftp_server.c:1209)
==3921==    by 0x804AEE8: main (uftp_server.c:1512)
==3921==  Address 0x41db2ac is not stack'd, malloc'd or (recently) free'd
==3921== 
==3921== Invalid write of size 1
==3921==    at 0x8049A9C: download_build_buffer (uftp_server.c:792)
==3921==    by 0x8049F4C: server_download_file (uftp_server.c:989)
==3921==    by 0x804A4E1: data_connection_proc (uftp_server.c:1209)
==3921==    by 0x804AEE8: main (uftp_server.c:1512)
==3921==  Address 0x41db2b0 is not stack'd, malloc'd or (recently) free'd
==3921== 
server_download_file 3921: download finished
--3921-- VALGRIND INTERNAL ERROR: Valgrind received a signal 11 (SIGSEGV) - exiting
--3921-- si_code=1;  Faulting address: 0x0;  sp: 0x62af9e0c

valgrind: the 'impossible' happened:
Killed by fatal signal
==3921==    at 0x38034171: unlinkBlock (m_mallocfree.c:244)

sched status:
running_tid=1

Thread 1: status = VgTs_Runnable
==3921==    at 0x4026864: malloc (vg_replace_malloc.c:236)
==3921==    by 0x804911B: file_release_lock (uftp_server.c:423)
==3921==    by 0x8049DE9: server_download_file (uftp_server.c:930)
==3921==    by 0x804A4E1: data_connection_proc (uftp_server.c:1209)
==3921==    by 0x804AEE8: main (uftp_server.c:1512)

万一,请问我其他信息,谢谢

编辑在最后一次memcpy之前,dim_payload用htonl()转换为网络格式并从512传递到131072 ..它需要使用ntohl()返回512.

Answer 1

你不应该有副作用assert.在没有它们的情况下编译时,它们的表达式将被忽略.在这种情况下,以下可能会导致您的问题:

assert((buffer = malloc((dim_payload+1)*sizeof(char)))
           != NULL);

我会用以下代替:

buffer = malloc((dim_payload+1)*sizeof(char));
assert(buffer != NULL);

哦,还有,sizeof(char)就是总是 1,所以你可以丢弃.