Re: [PATCH v3 1/1] tools/tests/x86_emulator: avoid duplicate symbol error with clang: use -O0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.03.2026 17:25, Edwin Török wrote:
> clang would duplicate the loop body and end up with a double definition
> of the symbol:
> ```
> /tmp/test_x86_emulator-0f3576.s:27823: Error: symbol `vmovsh_to_mem' is 
> already defined
> /tmp/test_x86_emulator-0f3576.s:27825: Error: symbol `.Lvmovsh_to_mem_end' is 
> already defined
> ```
> 
> Until a better solution is found: disable all optimizations in the test 
> runner.
> 
> Using -Os might also work, but we can't rely on the size optimization
> always avoiding the duplication of asm blocks.
> This is test code, not performance critical code, and -O0 is more future
> proof.

Hmm, yes, the good thing is that this then doesn't even conflict with my
https://lists.xen.org/archives/html/xen-devel/2023-04/msg00283.html.

> --- a/tools/tests/x86_emulator/Makefile
> +++ b/tools/tests/x86_emulator/Makefile
> @@ -323,4 +323,9 @@ x86-emulate.o x86_emulate/%.o: HOSTCFLAGS += 
> -D__XEN_TOOLS__
>  $(call cc-option-add,HOSTCFLAGS-toplevel,HOSTCC,-fno-toplevel-reorder)
>  test_x86_emulator.o: HOSTCFLAGS += $(HOSTCFLAGS-toplevel)
>  
> +# clang duplicates inline assembly when unrolling loops,
> +# which causes a duplicate label error.
> +# Until a better solution is found: disable all optimizations in the test 
> runner.
> +test_x86_emulator.o: HOSTCFLAGS += -O0

I think the first sentence may want wording a little differently, and I
further think it absolutely needs to mention put_insn(). Maybe:

"When unrolling loops, compilers may duplicate inline assembly. put_insn()
 emits labels, which may not be emitted multiple times."

Happy to adjust while committing if you're okay with me doing so. There's
one other question though: Isn't -O0 the default? Where would any other
optimization setting come from in HOSTCFLAGS? Ah, I see ./Config.mk does
this, for an unclear to me reason. Perhaps that would want mentioning
here then as well.

Jan