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Date: Thu, 7 Apr 2016 13:42:17 +0200
From: Sebastian Gottschall <>
Subject: Re: recvmsg/sendmsg broken on mips64

> ok so the failure is in sendmsg and in the msg_control copy.
> does the call fail with ENOMEM (because >1024 bytes of ancillary data)?
> that would be easy to fix..
> (libc has to make a copy, the struct is const and might be in
> readonly memory. a detailed bug report of the failure would
> be more useful than speculations about broken compilers..
> e.g. strace log with and without the msg_control copying.)
how to make a more detailed report than just that all netlink operations 
in iproute2 fail. so the whole ip command doesnt work.
i tracked it down to recvmsg / sendmsg which do not return in success 
for some reason. if i send it more detailed, which means i debug out
the real cause would also mean submit a better patch. just had no time 
yet to care about since my hack works.

but does not fit to your philosophy. its easy to reproduce on any octeon 
device using musl and iproute2.

>>          struct msghdr h;
>>          struct cmsghdr chbuf[1024/sizeof(struct cmsghdr)+1], *c;
>>          if (msg) {
>>                  h = *msg;
>>                  h.__pad1 = h.__pad2 = 0;
>>                  msg = &h;
>>                  if (h.msg_controllen) {
>>                          if (h.msg_controllen > 1024) {
>>                                  errno = ENOMEM;
>>                                  return -1;
>>                          }
>>                          memcpy(chbuf, h.msg_control, h.msg_controllen);
>>                          h.msg_control = chbuf;
>>                          for (c=CMSG_FIRSTHDR(&h); c; c=CMSG_NXTHDR(&h,c))
>>                                  c->__pad1 = 0;
>>                  }
>>          }
>> #endif

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