amd64/161949: [kern] 64-bit structures are used even with 32-bit
cdavis at mymail.mines.edu
Mon Oct 24 01:00:24 UTC 2011
>Synopsis: [kern] 64-bit structures are used even with 32-bit code
>Arrival-Date: Mon Oct 24 01:00:02 UTC 2011
>Originator: Charles Davis
Colorado School of Mines
FreeBSD <hostname> 8.2-RELEASE-p3 FreeBSD 8.2-RELEASE-p3 #0: Tue Sep 27 18:45:57 UTC 2011 root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC amd64
When a process transfers data to or from the kernel, and those data are organized into structures whose size depends on whether or not the size of a pointer is 4 or 8 bytes, an LP64 kernel always uses 64-bit structures, even with 32-bit processes. I know this is true of structures returned from sysctl(3), but I also think it is true of structures used with ioctl(2) and fcntl(2). Because 32-bit processes expect 32-bit structures, attempts to use the 64-bit structures fail at best and cause massive data corruption at worst.
This is already affecting real-world code. A patch of mine that was recently committed to Wine (http://www.winehq.org) exposed this issue with the xtcpcb and xinpcb structs returned by the sysctl(3)s "net.inet.tcp.pcblist" and "net.inet.udp.pcblist" (cf. Wine bug 28857: http://bugs.winehq.org/show_bug.cgi?id=28857).
Run any 32-bit program under a 64-bit kernel that calls sysctl(3), ioctl(2), or fcntl(2) and uses a data structure with those calls whose size depends on the pointer size.
FreeBSD should detect if a process is a 32-bit one, and if so, it should use 32-bit structures instead of 64-bit ones. I don't know how the former can be done; a cursory look through the <sys/proc.h> header reveals nothing. The latter is easy, but tedious: definitions for the 32-bit structs must be added to the kernel headers.
Another way to solve this problem (at the cost of binary compatibility for 32-bit programs) is to simply make the 32-bit and 64-bit structures the same.
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