Re: [RFC PATCH 0/3] kernel: add support for 256-bit IO access
flat view
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: 2018-03-19 16:29:30
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On Mon, Mar 19, 2018 at 8:53 AM, David Laight [off-list ref] wrote:
The x87 and SSE registers can't be changed - they can contain callee-saved registers. But (IIRC) the AVX and AVX2 registers are all caller-saved.
No.
The kernel entry is not the usual function call.
On kernel entry, *all* registers are callee-saved.
Of course, some may be return values, and I have a slight hope that I
can trash %eflags. But basically, a system call is simply not a
function call. We have different calling conventions on the argument
side too. In fact, the arguments are in different registers depending
on just *which* system call you take.
Linus