Re: build error while building arch/x86/purgatory/sha256.o: invalid 'asm': operand is not a condition code [...]

From: Kees Cook
Date: Tue May 30 2023 - 00:23:57 EST

On May 28, 2023 9:40:31 AM PDT, "Joan Bruguera Micó" <joanbrugueram@xxxxxxxxx> wrote:
>I can also reproduce the problem with Arch's linux-next-git, see config:
>I've bisected it to df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3"),
>which explains why it only happens on GCC13.
>The problematic expansion that causes the error seems to be this fragment
>from `_BUG_FLAGS` in `arch/x86/include/asm/bug.h`:
> asm(".long %c0 - .\n": : "i" (__FILE__));
>Along with the fact that this file is built with `-mcmodel=large`
>(see `PURGATORY_CFLAGS` in `arch/x86/purgatory/Makefile`).

I haven't reproduced this yet, but the error implies that the asm input "i"mmediate value of the __FILE__ string address cannot be used with the asm template format "%c0" (a constant value).

I cannot fathom why struct flex array logic would change that...

I'll take a closer look in the morning.


Kees Cook