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Date: Tue, 29 Oct 2019 13:35:40 -0700
From: Nick Desaulniers <>
To: Mark Rutland <>, Kristof Beyls <>
Cc: Will Deacon <>, Catalin Marinas <>, 
	Steven Rostedt <>, Masami Hiramatsu <>, 
	Ard Biesheuvel <>, Dave Martin <>, 
	Kees Cook <>, Laura Abbott <>, Jann Horn <>, 
	Miguel Ojeda <>, 
	Masahiro Yamada <>, 
	clang-built-linux <>, 
	Kernel Hardening <>, 
	linux-arm-kernel <>, LKML <>, 
	Sami Tolvanen <>
Subject: Re: [PATCH v2 09/17] arm64: disable function graph tracing with SCS

On Tue, Oct 29, 2019 at 10:45 AM Sami Tolvanen <> wrote:
> On Fri, Oct 25, 2019 at 4:03 AM Mark Rutland <> wrote:
> > We have a similar issue with pointer authentication, and we're solving
> > that with -fpatchable-function-entry, which allows us to hook the
> > callsite before it does anything with the return address. IIUC we could
> > use the same mechanism here (and avoid introducing a third).
> >
> > Are there plans to implement -fpatchable-function-entry on the clang
> > side?
> I'm not sure if there are plans at the moment, but if this feature is
> needed for PAC, adding it to clang shouldn't be a problem. Nick, did
> you have any thoughts on this?

I didn't see anything explicitly in LLVM's issue tracker.  I also
didn't see -fpatchable-function-entry currently in -next other than
under arch/parisc.  Are there patches I can look at?

Has ARM's kernel team expressed the need to ARM's LLVM team?
~Nick Desaulniers

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