What's the reason of this segmentation fault?

It doesn't happen always,but will happen when the server application has been running for quite a while.

What's the reason and how can I fix it?

Code as follows:

struct hostent* Host; Result->sin_family=AF_INET; Result->sin_port=htons((unsigned short)Port); Host=gethostbyname(HostName); if(!Host) { unsigned long int addr=inet_addr(HostName); if(addr!=-1) Host=gethostbyaddr(&addr,sizeof(addr),AF_INET); if(!Host) { if(errno!=ETIMEDOUT) errno=-1; /* use h_errno */ printf("Unknown host for server [%s].", HostName); return(0); } } memcpy((char*)&Result->sin_addr,(char*)Host->h_addr,sizeof(Result->sin_addr));

core dump:

#0 0x0000000000401913 in proxy_getaddr (HostName=0x7ae30be0 "stackoverflow.com", Port=80, Result=0x7ae30bd0) at proxy.c:529 529 memcpy((char*)&Result->sin_addr,(char*)Host->h_addr,sizeof(Result->sin_addr)); (gdb) p *Host $4 = {h_name = 0xc4ee048 "", h_aliases = 0xc4ee030, h_addrtype = 2, h_length = 4, h_addr_list = 0xc4ee038} (gdb) print Result $5 = (struct sockaddr_in *) 0x7ae30bd0 (gdb) print *Result $6 = {sin_family = 2, sin_port = 20480, sin_addr = {s_addr = 0}, sin_zero = "00000000000000"} (gdb) p Host->h_addr_list[0] $1 = 0x0 (gdb) p Host->h_addr_list $2 = (char **) 0x1bd9d050

-------------Problems Reply------------

Given that the Host and Result variables both point to legitimate blocks of memory, the most likely cause is that Host->h_addr is NULL. This would be the case if the list of addresses returned by gethostbyname() or gethostbyaddr() were empty.

I don't know how that could be caused (the documentation on my OS X system implies that both functions should return NULL if no addresses can be found). However, I would check Host->h_addr_list[0] in the debugger to confirm.


The update of the debug info shows where the problem is: Host->h_addr is NULL. h_addr is actually a #define like this:

#define h_addr h_addr_list[0]

One of the functions is returning a struct hostent with an empty address list.

Maybe, source and destination memory areas overlap? i.e.

&Result->sin_addr >= Host->h_addr >= &Result->sin_addr + sizeof(Result->sin_addr)

The memcpy is failing.

This could be caused by (1) sin_addr and h_addr are not the same sizes or (2) sin_addr is a pointer and you have not malloc'd memory for it.

Please provide the definition and initialisation of Result for more info.

Category:c# Views:0 Time:2011-05-23
Tags: coredump

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