[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [RFC v3 20/27] x86/ftrace: Adapt function tracing for PIE support



On Thu, Oct 5, 2017 at 6:06 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> On Wed,  4 Oct 2017 14:19:56 -0700
> Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
>
>> When using -fPIE/PIC with function tracing, the compiler generates a
>> call through the GOT (call *__fentry__@GOTPCREL). This instruction
>> takes 6 bytes instead of 5 on the usual relative call.
>>
>> With this change, function tracing supports 6 bytes on traceable
>> function and can still replace relative calls on the ftrace assembly
>> functions.
>>
>> Position Independent Executable (PIE) support will allow to extended the
>> KASLR randomization range below the -2G memory limit.
>
> Question: This 6 bytes is only the initial call that gcc creates. When
> function tracing is enabled, the calls are back to the normal call to
> the ftrace trampoline?

That is correct.

>
> -- Steve
>



-- 
Thomas

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.