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

[Segher Boessenkool]

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.


Segher