Re: [PATCH 1/2] kbuild: add '-fno-stack-check' to barebox build options

[Sascha Hauer <sha@pengutronix.de>]

On Tue, Feb 23, 2021 at 08:24:26AM +0100, Ahmad Fatoum wrote:
> This ports over Linux commit 3ce120b16cc5 ("kbuild: add
> '-fno-stack-check' to kernel build options"):
> 
>   Author:     Linus Torvalds <torvalds@linux-foundation.org>
> 
>     kbuild: add '-fno-stack-check' to kernel build options
> 
>     It appears that hardened gentoo enables "-fstack-check" by default for
>     gcc.
> 
>     That doesn't work _at_all_ for the kernel, because the kernel stack
>     doesn't act like a user stack at all: it's much smaller, and it doesn't
>     auto-expand on use.  So the extra "probe one page below the stack" code
>     generated by -fstack-check just breaks the kernel in horrible ways,
>     causing infinite double faults etc.
> 
>     [ I have to say, that the particular code gcc generates looks very
>       stupid even for user space where it works, but that's a separate
>       issue.  ]
> 
>     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> 
> I am porting it, because it may become more acute with the incoming
> support for multiple stacks (via initjmp).
> 
> Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
> ---

Applied, thanks

Sascha

>  Makefile | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index f3c85cff9430..fa7fbbeb35f0 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -622,6 +622,9 @@ KBUILD_CFLAGS += $(call cc-option, -fno-delete-null-pointer-checks,)
>  # disable invalid "can't wrap" optimizations for signed / pointers
>  KBUILD_CFLAGS	+= $(call cc-option,-fno-strict-overflow)
>  
> +# Make sure -fstack-check isn't enabled (like gentoo apparently did)
> +KBUILD_CFLAGS  += $(call cc-option,-fno-stack-check)
> +
>  KBUILD_CFLAGS   += $(call cc-disable-warning, address-of-packed-member)
>  
>  # Align the bit size of userspace programs with the kernel
> -- 
> 2.30.0
> 
> 
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