On Thu, Jun 26, 2014 at 12:08 PM, Andy Lutomirski wrote:
> The int_ret_from_sys_call and syscall tracing code disagrees with
> the sysret path as to the value of RCX.
>
> The Intel SDM, the AMD APM, and my laptop all agree that sysret
> returns with RCX == RIP. The syscall tracing code does not
On Thu, Jun 26, 2014 at 12:08 PM, Andy Lutomirski l...@amacapital.net wrote:
The int_ret_from_sys_call and syscall tracing code disagrees with
the sysret path as to the value of RCX.
The Intel SDM, the AMD APM, and my laptop all agree that sysret
returns with RCX == RIP. The syscall tracing
On Sat, Jun 28, 2014 at 10:07 AM, Pavel Machek wrote:
> On Thu 2014-06-26 13:47:32, Andy Lutomirski wrote:
>> On Thu, Jun 26, 2014 at 1:12 PM, H. Peter Anvin wrote:
>> > The real question is if we care that sysret and iter don't match. On 32
>> > bits the situation is even more complex.
>>
>>
On Sat, Jun 28, 2014 at 10:07 AM, Pavel Machek pa...@ucw.cz wrote:
On Thu 2014-06-26 13:47:32, Andy Lutomirski wrote:
On Thu, Jun 26, 2014 at 1:12 PM, H. Peter Anvin h...@zytor.com wrote:
The real question is if we care that sysret and iter don't match. On 32
bits the situation is even
On Thu 2014-06-26 13:47:32, Andy Lutomirski wrote:
> On Thu, Jun 26, 2014 at 1:12 PM, H. Peter Anvin wrote:
> > The real question is if we care that sysret and iter don't match. On 32
> > bits the situation is even more complex.
>
> At least for 64 bits, iret vs sysret is purely a kernel
On Thu 2014-06-26 13:47:32, Andy Lutomirski wrote:
On Thu, Jun 26, 2014 at 1:12 PM, H. Peter Anvin h...@zytor.com wrote:
The real question is if we care that sysret and iter don't match. On 32
bits the situation is even more complex.
At least for 64 bits, iret vs sysret is purely a
On Thu, Jun 26, 2014 at 1:12 PM, H. Peter Anvin wrote:
> The real question is if we care that sysret and iter don't match. On 32 bits
> the situation is even more complex.
At least for 64 bits, iret vs sysret is purely a kernel implementation
detail (except where a tracer modifies things that
The real question is if we care that sysret and iter don't match. On 32 bits
the situation is even more complex.
On June 26, 2014 1:00:22 PM PDT, Andy Lutomirski wrote:
>On Thu, Jun 26, 2014 at 12:59 PM, Andy Lutomirski
>wrote:
>> On Thu, Jun 26, 2014 at 12:56 PM, Andi Kleen
>wrote:
On Thu, Jun 26, 2014 at 12:59 PM, Andy Lutomirski wrote:
> On Thu, Jun 26, 2014 at 12:56 PM, Andi Kleen wrote:
>>> show RCX == RIP even under strace.
>>
>> If you think it's really worth the extra instruction?
>
> Hard to say. That extra instruction only happens on slow paths, so I
> suspect
On Thu, Jun 26, 2014 at 12:56 PM, Andi Kleen wrote:
>> show RCX == RIP even under strace.
>
> If you think it's really worth the extra instruction?
Hard to say. That extra instruction only happens on slow paths, so I
suspect the slowdown is negligible. On the other hand, having syscall
show a
> show RCX == RIP even under strace.
If you think it's really worth the extra instruction?
It's not wrong, but it's not clear if it's useful.
-Andi
>
> Signed-off-by: Andy Lutomirski
> ---
> arch/x86/kernel/entry_64.S | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git
The int_ret_from_sys_call and syscall tracing code disagrees with
the sysret path as to the value of RCX.
The Intel SDM, the AMD APM, and my laptop all agree that sysret
returns with RCX == RIP. The syscall tracing code does not respect
this property.
For example, this program:
int main()
{
The int_ret_from_sys_call and syscall tracing code disagrees with
the sysret path as to the value of RCX.
The Intel SDM, the AMD APM, and my laptop all agree that sysret
returns with RCX == RIP. The syscall tracing code does not respect
this property.
For example, this program:
int main()
{
show RCX == RIP even under strace.
If you think it's really worth the extra instruction?
It's not wrong, but it's not clear if it's useful.
-Andi
Signed-off-by: Andy Lutomirski l...@amacapital.net
---
arch/x86/kernel/entry_64.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
On Thu, Jun 26, 2014 at 12:56 PM, Andi Kleen a...@firstfloor.org wrote:
show RCX == RIP even under strace.
If you think it's really worth the extra instruction?
Hard to say. That extra instruction only happens on slow paths, so I
suspect the slowdown is negligible. On the other hand, having
On Thu, Jun 26, 2014 at 12:59 PM, Andy Lutomirski l...@amacapital.net wrote:
On Thu, Jun 26, 2014 at 12:56 PM, Andi Kleen a...@firstfloor.org wrote:
show RCX == RIP even under strace.
If you think it's really worth the extra instruction?
Hard to say. That extra instruction only happens on
The real question is if we care that sysret and iter don't match. On 32 bits
the situation is even more complex.
On June 26, 2014 1:00:22 PM PDT, Andy Lutomirski l...@amacapital.net wrote:
On Thu, Jun 26, 2014 at 12:59 PM, Andy Lutomirski l...@amacapital.net
wrote:
On Thu, Jun 26, 2014 at
On Thu, Jun 26, 2014 at 1:12 PM, H. Peter Anvin h...@zytor.com wrote:
The real question is if we care that sysret and iter don't match. On 32 bits
the situation is even more complex.
At least for 64 bits, iret vs sysret is purely a kernel implementation
detail (except where a tracer modifies
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