Re: [PATCH 13/15] arm64: fix mrs_s/msr_s macros for clang LTO

[Yury Norov]

Hi Sami,

(CC Andi Kleen, Alex Matveev, Maxim Kuvyrkov)

On Fri, Nov 03, 2017 at 10:12:01AM -0700, Sami Tolvanen wrote:
> Clang's integrated assembler does not allow assembly macros defined
> in one inline asm block using the .macro directive to be used across
> separate asm blocks. LLVM developers consider this a feature and not a
> bug, recommending code refactoring:
> 
>   https://bugs.llvm.org/show_bug.cgi?id=19749
> 
> As binutils doesn't allow macros to be redefined, this change adds C
> preprocessor macros that define the assembly macros globally for binutils
> and locally for clang's integrated assembler.

This macros are also the problem for gcc and ld.bfd if we try to
enable LTO.

The patch below uses trick with undefining mrs_s/msr_s immediately
after use to solve the problem. It works for both gcc and clang.

There's the series from Andi Kleen that enables LTO for Linux on x86:
https://lwn.net/Articles/512548/
https://github.com/andikleen/linux-misc/tree/lto-411-1

It has solved many problems you also try to solve, and some patches
are looking very similar. 

At now we have different patchsets for gcc and clang, and it would be
better to have them together. One thing I'm worried is that you introduce
CONFIG_CLANG_LTO and use it for all cases, including that where more
generic CONFIG_LTO should be used.

I think we'd also discuss it here.
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