Re: [PATCH 3/3] powerpc: Include -m32 / -m64 for stack protector Kconfig test

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 08/10/2024 à 06:22, Nathan Chancellor a écrit :
> Kbuild uses the powerpc64le-linux-gnu target for clang, which causes the
> Kconfig check for 32-bit powerpc stack protector support to fail because
> nothing flips the target to 32-bit:
> 
>    $ clang --target=powerpc64le-linux-gnu \
>            -mstack-protector-guard=tls
>            -mstack-protector-guard-reg=r2 \
>            -mstack-protector-guard-offset=0 \
>            -x c -c -o /dev/null /dev/null
>    clang: error: invalid value 'r2' in 'mstack-protector-guard-reg=', expected one of: r13

Why is there any restriction at all on which register can be used ? I 
can't see such restriction in GCC documentation : 
https://gcc.gnu.org/onlinedocs/gcc/RS_002f6000-and-PowerPC-Options.html



> 
> Use the Kconfig macro '$(m32-flag)', which expands to '-m32' when
> supported, in the stack protector support cc-option call to properly
> switch the target to a 32-bit one, which matches what happens in Kbuild.
> While the 64-bit macro does not strictly need it, add the equivalent
> 64-bit option for symmetry.
> 
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>   arch/powerpc/Kconfig | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index eb98050b8c016bb23887a9d669d29e69d933c9c8..6aaca48955a34b2a38af1415bfa36f74f35c3f3e 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -275,8 +275,8 @@ config PPC
>   	select HAVE_RSEQ
>   	select HAVE_SETUP_PER_CPU_AREA		if PPC64
>   	select HAVE_SOFTIRQ_ON_OWN_STACK
> -	select HAVE_STACKPROTECTOR		if PPC32 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r2 -mstack-protector-guard-offset=0)
> -	select HAVE_STACKPROTECTOR		if PPC64 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r13 -mstack-protector-guard-offset=0)
> +	select HAVE_STACKPROTECTOR		if PPC32 && $(cc-option,$(m32-flag) -mstack-protector-guard=tls -mstack-protector-guard-reg=r2 -mstack-protector-guard-offset=0)
> +	select HAVE_STACKPROTECTOR		if PPC64 && $(cc-option,$(m64-flag) -mstack-protector-guard=tls -mstack-protector-guard-reg=r13 -mstack-protector-guard-offset=0)

You modify the exact same line than Patch 1, if this patch is really 
required it should be squashed into patch 1 I think.

>   	select HAVE_STATIC_CALL			if PPC32
>   	select HAVE_SYSCALL_TRACEPOINTS
>   	select HAVE_VIRT_CPU_ACCOUNTING
>