Re: [PATCH v2 11/18] arm64: make mrs_s and msr_s macros work with LTO

From: Segher Boessenkool
Date: Thu Nov 16 2017 - 12:10:07 EST

On Thu, Nov 16, 2017 at 08:46:08AM -0800, Sami Tolvanen wrote:
> On Thu, Nov 16, 2017 at 07:56:50AM -0600, Segher Boessenkool wrote:
> > The compiler is fine, the assembler is fine (and the linker has
> > nothing to do with it). Your code is not fine.
> Would you care to elaborate? The current code assumes that macros are
> visible in other inline assembly blocks, and LLVM developers seem to
> feel this isn't correct behavior. This patch fixes the current code so
> it works with both assemblers.

If you say e.g.

void f(void)
asm(".macro something\n\t.endm");

there is nothing that prevents the compiler from emitting this more
than once. Expecting things to be emitted in whatever order is a bad
idea, too.

The thing with .purgem can work. Inelegant, sure, but it can work :-)
Just make sure you do the macro define, the code that uses it, and the
undefine, all in the same inline asm statement.