Re: [PATCH 0/2] ftrace: fixes for PPC

From: Josh Boyer
Date: Mon Oct 20 2008 - 13:21:51 EST

On Mon, Oct 20, 2008 at 12:30:33PM -0400, Steven Rostedt wrote:
>> Anyway, if you want a tester let me know. It seems should be
>> fine since FTRACE was disabled, but for .28-rc1 it would be cool if it
>> worked :).
>Hi Josh,
>I've been looking deeper at the code for PPC. I realized that my PPC64 box
>that I've been testing on did not use modules. While looking at the module
>code it dawned on me the dynamic ftrace needs a bit of work. This is
>because the way modules are handled in PPC (and other architectures as
>well). The jmps used by mcount is a 24 bit jump. Since the modules are
>loaded farther than 24bits away, a trampoline is needed.

Ah, indeed.

>A bit of rework is needed in the ftrace infrastructure to handle the
>trampoline. Too much work to go into 28. I'll start working on code that
>can hopefully be ready and tested for 29. It's not that major of a change,
>but since the merge window for 28 has already been opened, we would like
>to get a bit more testing in before we hand it over to Linus.

That seems like a good plan. Should we mark dynamic ftrace as X86 only
in Kconfig for .28 to prevent people from inadvertently setting it?

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