Re: [PATCH] x86: assemble with -Wa,--noexecstack to avoid BFD 2.39 warning

[Fangrui Song]

On 2022-08-08, Linus Torvalds wrote:
> On Mon, Aug 8, 2022 at 1:32 PM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote:
> > Thanks for the link; I recall Ard mentioning the ELF segments are
> > ignored by the kernels loader in another thread.
>
> Yeah, the kernel loader is not some generic ELF loader thing.
>
> > Perhaps we should be adding
> > --no-warn-execstack
> > wrapped in an ld-option check to KBUILD_LDFLAGS at the top level?
>
> I think both the linker flag and the assembler flag are the "correct"
> thing to do.
>
> And yes, I don't think there is anything architecture-specific about
> it, and the top-level Makefile is likely the right thing to modify.
>
> I'm a tiny bit worried about "what versions of as/ld accept those
> flags", though.
>
>              Linus

If most ports don't need executable stacks, I think using `-z
noexecstack` is better than the binutils 2.39 specific
--no-warn-execstack (not recognized by lld and older GNU ld, so a
configure check will be needed).

Then -Wa,--noexecstack is not necessary: if the built relocatable files
are destined to be used with ld with -z noexecstack, the input
.note.GNU-stack sections are really redundant. It would be a difficult
story if the relocatable files can "leak" to the outside world where a
GNU ld without -z noexecstack may be used. But IMO this is not the case
for the kernel.