Subject: Re: [1/2] powerpc/ftrace: Separate the heuristics for checking call sites

From: Michael Ellerman <[email-masked]>
Date: Fri, 22 Jul 2016 15:50:42 +1000 (AEST)

On Tue, 2016-19-07 at 04:48:30 UTC, Michael Ellerman wrote:
> In __ftrace_make_nop() (the 64-bit version), we have code to deal with
> two ftrace ABIs. There is the original ABI, which looks mostly like a
> function call, and then the mprofile-kernel ABI which is just a branch.
> 
> The code tries to handle both cases, by looking for the presence of a
> load to restore the TOC pointer (PPC_INST_LD_TOC). If we detect the TOC
> load, we assume the call site is for an mcount() call using the old ABI.
> That means we patch the mcount() call with a b +8, to branch over the
> TOC load.
> 
> However if the kernel was built with mprofile-kernel, then there will
> never be a call site using the original ftrace ABI. If for some reason
> we do see a TOC load, then it's there for a good reason, and we should
> not jump over it.
> 
> So split the code, using the existing CC_USING_MPROFILE_KERNEL. Kernels
> built with mprofile-kernel will only look for, and expect, the new ABI,
> and similarly for the original ABI.
> 
> Signed-off-by: Michael Ellerman <[email-masked]>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/9d636109511a000882f8dff4ea

cheers