Commit 573deec0 authored by Joshua Kinard's avatar Joshua Kinard Committed by James Hogan

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 <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: default avatarJoshua Kinard <kumba@gentoo.org>
Suggested-by: default avatarJames Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15132/Signed-off-by: default avatarJames Hogan <james.hogan@imgtec.com>
parent 93e502b3
...@@ -131,6 +131,21 @@ cflags-$(CONFIG_CPU_LITTLE_ENDIAN) += $(shell $(CC) -dumpmachine |grep -q 'mips. ...@@ -131,6 +131,21 @@ cflags-$(CONFIG_CPU_LITTLE_ENDIAN) += $(shell $(CC) -dumpmachine |grep -q 'mips.
cflags-$(CONFIG_SB1XXX_CORELIS) += $(call cc-option,-mno-sched-prolog) \ cflags-$(CONFIG_SB1XXX_CORELIS) += $(call cc-option,-mno-sched-prolog) \
-fno-omit-frame-pointer -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. # CPU-dependent compiler/assembler options for optimization.
# #
......
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