Re: [PATCH 5/5] x86/asm/entry/32: Simplify ptrace register shuffling

Andy Lutomirski
2015-06-09T18:59:37Z

On Tue, Jun 9, 2015 at 11:54 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
> Before this patch, we were clearing pt_regs->r8..r11 on stack.
> We can as well just store actual r8..r11 registers there:
> they came from userspace, we leak no information by showing them to ptrace.
> This allows to get rid of one insn ("xor %eax,%eax").
> Not a big deal, but still...
>
> After call to syscall_trace_enter(), before this patch we were restoring
> clobbered registers and jump to code which converts 32-bit syscall
> ABI to 64-bit C ABI. This is unnecessary work, we can combine both
> steps into one (similar to what audit code does already).

I think like zeroing it better. There's nothing wrong with zeroing
it, and it makes testing (if we ever started testing this stuff)
easier, I think.

--Andy