Re: x86-32: Early microcode loading stumbles over disabled DYNAMIC_FTRACE

[H. Peter Anvin]

On 08/30/2013 10:03 AM, Steven Rostedt wrote:
> On Fri, 30 Aug 2013 09:35:18 -0700
> "H. Peter Anvin" <hpa@xxxxxxxxx> wrote:
> 
>> On 08/30/2013 08:51 AM, Steven Rostedt wrote:
>>>
>>> It does when dynamic tracing is enabled. But this issue is with static
>>> tracing, there's no code modification, thus all functions call
>>> mcount/__fentry__ and we need to look at a variable to determine if we
>>> should trace or not.
>>>
>>
>> And of course global variables are a no-no without special handling in
>> pre-paging mode.  Sigh.
>>
>> You *could* bail out of the calling address is < PAGE_OFFSET.
>>
> 
> We could do that too, as static tracing already gives us high overhead,
> I'm not sure how much more overhead another check like this even
> matters.
> 
> Who uses static tracing? I only use it to test that it still works ;-)
> 

Anyway... can we add this to the static tracing code?  It is two
instructions and is only needed on x86-32.  For performance, use dynamic.

	-hpa


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/