From: Joshua Kinard <kumba@xxxxxxxxxx> 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@xxxxxxxxxx> Suggested-by: James Hogan <james.hogan@xxxxxxxxxx> --- 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. #
