Using ftrace

Using ftrace

[Glenn Washburn]

I'm trying to use the ftrace facility within UML. It appears as though
it exists in the menuconfig, but I can't seem to get the kernel to
recognize the tracefs filesystem. I'm wondering if someone can confirm
that either ftrace does or does not work in UML.

Thanks,
Glenn

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Re: Using ftrace

[Anton Ivanov]

On 31/01/2023 04:17, Glenn Washburn wrote:
> I'm trying to use the ftrace facility within UML. It appears as though
> it exists in the menuconfig, but I can't seem to get the kernel to
> recognize the tracefs filesystem. I'm wondering if someone can confirm
> that either ftrace does or does not work in UML.

I have not used it. We have not had any requests related to it either

I will look into it.

Brgds,

> 
> Thanks,
> Glenn
> 
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> 


-- 
Anton R. Ivanov
https://www.kot-begemot.co.uk/

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Re: Using ftrace

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "Anton Ivanov" <anton.ivanov@kot-begemot.co.uk>
> On 31/01/2023 04:17, Glenn Washburn wrote:
>> I'm trying to use the ftrace facility within UML. It appears as though
>> it exists in the menuconfig, but I can't seem to get the kernel to
>> recognize the tracefs filesystem. I'm wondering if someone can confirm
>> that either ftrace does or does not work in UML.
> 
> I have not used it. We have not had any requests related to it either
> 
> I will look into it.

Tracing itself should work. But function tracing is not supported.
You'll get tracefs as soon you select one tracer (such as CONFIG_IRQSOFF_TRACER).

Adding function (and function graph) tracing to UML is possible but a bit of work.
You need to find a way to implement all of ftraces mcount hooks for UML.

Thanks,
//richard

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Re: Using ftrace

[Johannes Berg]

On Tue, 2023-01-31 at 08:22 +0100, Richard Weinberger wrote:
> 
> Adding function (and function graph) tracing to UML is possible but a bit of work.
> You need to find a way to implement all of ftraces mcount hooks for UML.
> 

It feels like it shouldn't be that hard, but I coincidentally looked a
few days ago and got scared :)

johannes

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Re: Using ftrace

[Anton Ivanov]

On 31/01/2023 09:10, Johannes Berg wrote:
> On Tue, 2023-01-31 at 08:22 +0100, Richard Weinberger wrote:
>> Adding function (and function graph) tracing to UML is possible but a bit of work.
>> You need to find a way to implement all of ftraces mcount hooks for UML.
>>
> It feels like it shouldn't be that hard, but I coincidentally looked a
> few days ago and got scared :)
Isn't that nearly always the case with UML?
>
> johannes
>
-- 
Anton R. Ivanov
https://www.kot-begemot.co.uk/


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Re: Using ftrace

[YiFei Zhu]

On Tue, Jan 31, 2023 at 1:11 AM Johannes Berg <johannes@sipsolutions.net> wrote:
>
> On Tue, 2023-01-31 at 08:22 +0100, Richard Weinberger wrote:
> >
> > Adding function (and function graph) tracing to UML is possible but a bit of work.
> > You need to find a way to implement all of ftraces mcount hooks for UML.
> >
>
> It feels like it shouldn't be that hard, but I coincidentally looked a
> few days ago and got scared :)

This looks interesting. I might want to take a look too soon. ;)

YiFei Zhu

> johannes
>
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Re: Using ftrace

[Glenn Washburn]

On Tue, 31 Jan 2023 08:22:45 +0100 (CET)
Richard Weinberger <richard@nod.at> wrote:

> ----- Ursprüngliche Mail -----
> > Von: "Anton Ivanov" <anton.ivanov@kot-begemot.co.uk>
> > On 31/01/2023 04:17, Glenn Washburn wrote:
> >> I'm trying to use the ftrace facility within UML. It appears as
> >> though it exists in the menuconfig, but I can't seem to get the
> >> kernel to recognize the tracefs filesystem. I'm wondering if
> >> someone can confirm that either ftrace does or does not work in
> >> UML.
> > 
> > I have not used it. We have not had any requests related to it
> > either
> > 
> > I will look into it.
> 
> Tracing itself should work. But function tracing is not supported.
> You'll get tracefs as soon you select one tracer (such as
> CONFIG_IRQSOFF_TRACER).

Okay, that makes sense. Yes, I was really asking about function
tracing.

> Adding function (and function graph) tracing to UML is possible but a
> bit of work. You need to find a way to implement all of ftraces
> mcount hooks for UML.

Sounds like more than I want to invest at this point. I'll get on
without it for the time being. Thanks for the confirmation. 

Glenn

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