Hi Arnd,

On Thu, Feb 1, 2018 at 12:46 PM, Arnd Bergmann [off-list ref] wrote:

On Thu, Feb 1, 2018 at 11:21 AM, Geert Uytterhoeven
[off-list ref] wrote:

quoted

Gcc versions before 4.4 do not recognize the __optimize__ compiler
attribute:

    warning: ‘__optimize__’ attribute directive ignored

Fixes: 7375ae3a0b79ea07 ("compiler-gcc.h: Introduce __nostackprotector function attribute")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Can anyone please verify this?
Apparently __nostackprotector is used on x86 only, which is usually
served by modern compilers.

I've checked that __optimize("no-stack-protector") is accepted by exactly those
compilers that your 40400 version check tests for, across all architectures, so
that's fine.

Thanks!

However,  looking at commit 91cfc88c66bf ("x86: Use __nostackprotect for
sme_encrypt_kernel"), I suspect that gcc-4.1 through 4.3 will now cause
a runtime failure in sme_encrypt_kernel() without a compile-time warning.

So having this functionality is a hard requirement. Oops...

I would leave __nostackprotector unchanged here, so we at least get
a warning for functions that need to disable the stack protector to work
correctly.

Agreed.

We might want to add an #ifdef CONFIG_CC_STACKPROTECTOR around
the __nostackprotector definition, so that we only warn if stackprotector
is globally enabled.

And we might want to remove the dummy in include/linux/compiler_types.h:

#ifndef __nostackprotector
# define __nostackprotector
#endif

BTW, how does this work with non-gcc compilers?

Gr{oetje,eeting}s,

                        Geert