sysctl in a NSAutoreleasePool -> bus errors & segfaults
Thanks in advance to everyone trying to help me. I'm having a big issue here, I've found some example code about sysctl and extended it so I can query the network interfaces for their in/out data. When I run this code directly in main() (without any NSAutoreleasePool) everything works fine. However, once I add it to my class and execute it I get bus errors & segfaults. I've tracked the issue down to NSAutoreleasePools. Can anybody please help? (If you don't believe it, just place a NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; before the code 开发者_StackOverflow中文版and place the whole thing into main())
int mib[] = { CTL_NET, PF_ROUTE, 0, 0, NET_RT_IFLIST, 0 };
int alloc;
struct if_msghdr *ifm, *nextifm;
struct sockaddr_dl *sdl;
char *lim, *next;
size_t needed;
char s[32];
char* buf;
if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
return 0;
if (alloc < needed) {
buf = malloc(needed);
if (buf == NULL)
return 0;
alloc = needed;
}
if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0)
return 0;
lim = buf + needed;
next = buf;
while (next < lim) {
ifm = (struct if_msghdr *)next;
if (ifm->ifm_type != RTM_IFINFO)
return 0;
next += ifm->ifm_msglen;
while (next < lim) {
nextifm = (struct if_msghdr *)next;
if (nextifm->ifm_type != RTM_NEWADDR)
break;
next += nextifm->ifm_msglen;
}
if (ifm != NULL && ifm->ifm_flags & IFF_UP) {
sdl = (struct sockaddr_dl *)(ifm + 1);
if (sdl->sdl_family != AF_LINK)
continue;
strncpy(s, sdl->sdl_data, sdl->sdl_nlen);
s[sdl->sdl_nlen] = '\0';
NSLog(@"interface %s in %qu out %qu \n", s,(UInt64)ifm->ifm_data.ifi_ibytes, (UInt64)ifm->ifm_data.ifi_obytes );
}
}
The NSAutoreleasePool
isn't the problem. It just reveals that you have a problem with memory allocation, double releases, dangling pointers or uninitialized data.
In your case, it's uninitialized data. You don't initialize the alloc
variable. As a consequence, it's completely random whether buf
is allocated or is pointing to some random memory location.
My hunch is it's to do with your misuse of strncpy()
. You're copying sdl->sdl_nlen
characters. If this is larger than 32, then you're overflowing your buffer. If it's exactly 32, then your assignment of \0
is outside of s[]
(likely in buf
).
In either case, you're passing some kind of illegal memory to NSLog()
, which itself generates autoreleased variables. Likely one of those is responsible for the crash when the pool drains.
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