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

- From: H. Peter Anvin \<hidden\>
- Date: 2016-07-04 20:24:39 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/07/4788143
- Thread: https://ratatoskr.run/linux-api/2016/07/4788017/t.md

```text
On July 4, 2016 1:13:21 PM PDT, "Tautschnig, Michael" [ref] wrote:
>
>> On 4 Jul 2016, at 20:27, H. Peter Anvin [ref] wrote:
>> 
>> On July 4, 2016 6:52:58 AM PDT, "Tautschnig, Michael"
>[ref] 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.
>>> 
>>> 
>[...]
>> 
>> 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

That, and tracing.
-- 
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```