Re: [Xen-devel] [RFC PATCH 4/7] build: convert frame_pointer to Kconfig

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.05.16 at 17:25, <konrad.wilk@xxxxxxxxxx> wrote:
> On Sun, May 01, 2016 at 11:10:43PM -0500, Doug Goldstein wrote:
>> --- a/xen/Kconfig.debug
>> +++ b/xen/Kconfig.debug
>> @@ -15,6 +15,14 @@ config CRASH_DEBUG
>>        If you want to be able to attach gdb to Xen to be able to debug
>>        Xen if it crashes then say Y.
>>  
>> +config FRAME_POINTER
>> +    bool "Compile Xen with frame pointers"
>> +    default y
>> +    ---help---
>> +      If you say Y here the resulting Xen will be slightly larger and
>> +      maybe slower, but it gives very useful debugging information
> 
> The extra cost is:
> 
>  leaq  offs(%rsp),%rbp;
>  notq  %rbp   
> 
> On entry in hypervisor.

An higher register pressure.

> Perhaps just say two extra operations are added on every vmexit ?
> 
> Is there an use-case for _not_ having frame pointers?

Yes - having one more register available for the compiler to put
data in. That's why we build with frame pointers in debug mode
only by default.

Jan


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