Re: [PATCH] zap linking-only option from EMBEDDED_EXTRA_CFLAGS

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.09.2022 16:29, Andrew Cooper wrote:
> On 27/09/2022 15:14, Roger Pau Monne wrote:
>> On Fri, Sep 09, 2022 at 09:22:52AM +0200, Jan Beulich wrote:
>>> While I was suspicious of the compiler issuing a diagnostic about an
>>> unused linking-only option when not doing any linking, I did check this
>>> with a couple of gcc versions only, but not with Clang. (Oddly enough at
>>> least older Clang versions complain about the use of '-nopie' now that
>>> we actually use '-no-pie'.) Filter out the problematic option in all
>>> cases where the variable is consumed for compilation only (which right
>>> now is everywhere).
>>>
>>> Fixes: ecd6b9759919 ("Config.mk: correct PIE-related option(s) in 
>>> EMBEDDED_EXTRA_CFLAGS")
>>> Reported-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> ---
>>> Arguably with all users of EMBEDDED_EXTRA_CFLAGS using these just for
>>> compiling, the option could be omitted from that variable right away.
>>> But if any compile-and-link-in-one-go use appeared, there would be an
>>> issue.
>> Is it feasible to have compile-and-link-in-one-go in one use feasible
>> with what we consider embedded (firmware or kernel like binaries).  I
>> would expect those to always require a linker script and a separate
>> linking step.
> 
> As I've expressed several times previously, the entire variable is bogus.
> 
> Just because we do have several things which are built as
> non-freestanding, doesn't mean they share a common CLFLAGS environment.
> 
> PIE is very specific to the intended use, and blindly disabling the
> stack protector isn't safe either.  It only works because none of our
> freestanding environments have gone to the effort of adding stack
> protector support.
> 
> -fno-exceptions is furthermore bogus in CLFLAGS, as its a CXXFLAG only.
> 
> And no, this mess can't plausibly be used for a compile and link in one
> go.  Filtering out a non-CFLAG from the collection at every call site is
> nonsense.

So what do you suggest we do in the short term?

Jan