Re: [PATCH] Syscall arguments are unsigned long (full registers)

On 4 Jul 2016, at 20:27, H. Peter Anvin [off-list ref] wrote:

On July 4, 2016 6:52:58 AM PDT, "Tautschnig, Michael" [off-list ref] wrote:

quoted

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.

[...]

Wrong.  Syscall arguments aren't necessarily full registers, and on x86 truncation is already done by the callee, so we don't need any special handing.  Some other architectures have other constraints. 

Ok - I'm assuming I have thus misunderstood eb974c62565072e10c1422eb3205f5b611dd99a1 ? Supposedly all those SYSCALL_DEFINEx are required for other architectures only?

Best,
Michael