On Mon, Aug 22, 2011 at 6:13 PM, Al Viro <v...@zeniv.linux.org.uk> wrote:
>
> *UGH*. OK,
> 1) I'm an idiot; int_ret_from_sys_call does *not* usually step on
> rbp (it's callee-saved). So normally ebp is left as is on the way out,
> which is why we don't see stuff getting buggered left, right and center.
Check.
And the system call restart should actually work fine too, because at
syscall entry we save %ebp *both* in the slot for ebp and ecx when we
enter the first time. So the second time, we'll re-load the third
argument from ebp again, but that's fine - it's still going to be the
right value. Yes? No?
However, I note that the cstar entrypont has a comment about not saving ebp:
* %ebp Arg2 [note: not saved in the stack frame, should not be touched]
which sounds odd. Why don't we save it? If we take a signal handler
there, don't we want %ebp on the kernel stack in pt_regs, in order to
do everything right?
Now I'm *really* confused.
Linus
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