Re: Ancillary data and 32/64 bit processes
Re: Ancillary data and 32/64 bit processes
- Subject: Re: Ancillary data and 32/64 bit processes
- From: Kevin Van Vechten <email@hidden>
- Date: Sun, 03 Feb 2008 22:18:30 -0800
On Feb 3, 2008, at 11:15 AM, Michael Tuexen wrote:
I habe a problem using ancillary data on 64-bit processes...
The macro CMSG_DATA ist defined in /usr/include/sys/socket.h as
#define CMSG_DATA(cmsg) ((unsigned char *)(cmsg) + \
__DARWIN_ALIGN(sizeof(struct
cmsghdr)))
__DARWIN_ALIGN behaves different on 32-bit processes and 64-bit
processes.
Therefore the offset of the CMSG_DATA is 12 bytes on 32-bit processes
and 16 byte on 64-bit processes. However, the kernel ignores this
difference
and puts the CMSG_DATA at a 12 byte offset.
User processes may be 32-bit or 64-bit, but the kernel always executes
in a 32-bit address space.
Therefore programs using ancillary data work, when compiled for 32-
bit,
but do not work when compiled for 64-bit.
I can provide a simple UDP discard server which shows this bug.
Is this a known bug?
Please file a bug <http://developer.apple.com/bugreporter/>. Even if
it's a known issue, additional reports help us gauge the overall
impact of the issue. (A quick check didn't find any issues reported
against CMSG_DATA or DARWIN_ALIGN.)
Should it be fixed by changing the CMSG_DATA
macros to behave the same on 32-bit and 64-bit processes or should
the kernel be changed to adjust the ancillary data?
I suspect the former, since that would preserve the binary
compatibility expectations of 64-bit processes with today's kernel.
This problem is crucial for our SCTP NKE, which uses ancillary
data a lot...
As a workaround, you could define your own CMSG_DATA macro.
- Kevin
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