From: James Hogan <james.hogan@imgtec.com>
To: Joshua Kinard <kumba@gentoo.org>
Cc: Ralf Baechle <ralf@linux-mips.org>,
"Maciej W. Rozycki" <macro@linux-mips.org>,
Linux/MIPS <linux-mips@linux-mips.org>
Subject: Re: [PATCH] MIPS: Disable stack checks on MIPS kernels
Date: Tue, 14 Feb 2017 10:08:02 +0000 [thread overview]
Message-ID: <20170214100802.GQ24226@jhogan-linux.le.imgtec.org> (raw)
In-Reply-To: <8d0e3484-c8bd-2559-0809-2631474a11f8@gentoo.org>
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On Sat, Jan 28, 2017 at 10:24:16PM -0500, Joshua Kinard wrote:
> From: Joshua Kinard <kumba@gentoo.org>
>
> Disable stack checking on MIPS kernels. Some distribution toolchains
> might pass the -fstack-check option to gcc. This results in a
> store-doubleword instruction being emitted at the top of all
> functions that checks the available stack space. E.g.,
>
> a80000000001d740 <per_cpu_init>:
> a80000000001d740: ffa0bfc0 sd zero,-16448(sp)
> a80000000001d744: 2405ffc9 li a1,-55
> a80000000001d748: 67bdffc0 daddiu sp,sp,-64
>
> Generally, this is undesirable, and especially on the SGI IP27
> platform, it will trigger a NULL pointer dereference in
> '_raw_spin_lock_irq' during early init.
>
> Signed-off-by: Joshua Kinard <kumba@gentoo.org>
> Suggested-by: James Hogan <james.hogan@imgtec.com>
Applied
Thanks
James
> ---
> arch/mips/Makefile | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> linux-mips-4.10-disable-stack-check.patch
> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> index 1a6bac7b076f..6b2a30442105 100644
> --- a/arch/mips/Makefile
> +++ b/arch/mips/Makefile
> @@ -131,6 +131,21 @@ cflags-$(CONFIG_CPU_LITTLE_ENDIAN) += $(shell $(CC) -dumpmachine |grep -q 'mips.
>
> cflags-$(CONFIG_SB1XXX_CORELIS) += $(call cc-option,-mno-sched-prolog) \
> -fno-omit-frame-pointer
> +
> +# Some distribution-specific toolchains might pass the -fstack-check
> +# option during the build, which adds a simple stack-probe at the beginning
> +# of every function. This stack probe is to ensure that there is enough
> +# stack space, else a SEGV is generated. This is not desirable for MIPS
> +# as kernel stacks are small, placed in unmapped virtual memory, and do not
> +# grow when overflowed. Especially on SGI IP27 platforms, this check will
> +# lead to a NULL pointer dereference in _raw_spin_lock_irq.
> +#
> +# In disassembly, this stack probe appears at the top of a function as:
> +# sd zero,<offset>(sp)
> +# Where <offset> is a negative value.
> +#
> +cflags-y += -fno-stack-check
> +
> #
> # CPU-dependent compiler/assembler options for optimization.
> #
>
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prev parent reply other threads:[~2017-02-14 10:08 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-29 3:24 [PATCH] MIPS: Disable stack checks on MIPS kernels Joshua Kinard
2017-02-14 10:08 ` James Hogan [this message]
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