From 573deec09436c9136fff6d78e0325e052a1ad6be Mon Sep 17 00:00:00 2001 From: Joshua Kinard Date: Sat, 28 Jan 2017 22:24:16 -0500 Subject: [PATCH] MIPS: Disable stack checks on MIPS kernels 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 : 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 Suggested-by: James Hogan Cc: Ralf Baechle Cc: "Maciej W. Rozycki" Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/15132/ Signed-off-by: James Hogan --- arch/mips/Makefile | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/mips/Makefile b/arch/mips/Makefile index 6ea306b28ae9..8ef9c02747fa 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,(sp) +# Where is a negative value. +# +cflags-y += -fno-stack-check + # # CPU-dependent compiler/assembler options for optimization. # -- GitLab