> On 4 Jul 2016, at 16:59, Arnd Bergmann <a...@arndb.de> wrote: > > On Monday, July 4, 2016 2:47:10 PM CEST Tautschnig, Michael wrote: >> Thanks a lot for the immediate feedback. >> >>> On 4 Jul 2016, at 16:28, Andi Kleen <a...@linux.intel.com> wrote: >>> >>> On Mon, Jul 04, 2016 at 01:52:58PM +0000, Tautschnig, Michael wrote: >>>> All syscall arguments are passed in as types of the same byte size as >>>> unsigned long (width of full registers). Using a smaller type without a >>>> cast may result in losing bits of information. In all other instances >>>> apart from the ones fixed by the patch the code explicitly introduces >>>> type casts (using, e.g., SYSCALL_DEFINE1). >>>> >>>> While goto-cc reported these problems at build time, it is noteworthy >>>> that the calling conventions specified in the System V AMD64 ABI do >>>> ensure that parameters 1-6 are passed via registers, thus there is no >>>> implied risk of misaligned stack access. >>> >>> Does this actually fix anything? >>> >> >> It will ensure the behaviour on 32 and 64-bit systems is consistent, i.e., >> no truncation occurs. This is to ensure that future uses of these syscalls ^^^ no *hidden*
>> do not face surprises. >> [...] > This is the same truncation that we do with SYSCALL_DEFINE2(), > clearing the top 32 bits of the 'code' parameter to ensure that > user space doesn't pass data unexpectedly. > > That change seems reasonable, but why not just use SYSCALL_DEFINE2() > directly for consistency with the other syscalls? > Happy to provide such an updated patch; Andi seemed less confident this should be going ahead? Best, Michael
