On Fri, Jul 24, 2020 at 06:02:32PM +0200, Joerg Roedel wrote: > From: Joerg Roedel <jroedel@xxxxxxx> > > The x86-64 ABI defines a red-zone on the stack: > > The 128-byte area beyond the location pointed to by %rsp is considered > to be reserved and shall not be modified by signal or interrupt > handlers. Therefore, functions may use this area for temporary data > that is not needed across function calls. In particular, leaf > functions may use this area for their entire stack frame, rather than > adjusting the stack pointer in the prologue and epilogue. This area is > known as the red zone. > > This is not compatible with exception handling, because the IRET frame > written by the hardware at the stack pointer and the functions to handle > the exception will overwrite the temporary variables of the interrupted > function, causing undefined behavior. So disable red-zones for the > pre-decompression boot code. > > Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> > --- > arch/x86/boot/Makefile | 2 +- > arch/x86/boot/compressed/Makefile | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile > index fe605205b4ce..4d6a16a47e9f 100644 > --- a/arch/x86/boot/Makefile > +++ b/arch/x86/boot/Makefile > @@ -66,7 +66,7 @@ targets += cpustr.h > > # --------------------------------------------------------------------------- > > -KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP > +KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -mno-red-zone > KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ > KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables This change seems unnecessary? REALMODE_CFLAGS means it uses -m16, so this isn't 64-bit code. [As an aside, we can drop the check for -m16 support in arch/x86/Makefile now that we've bumbed to 4.9] > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile > index 5a828fde7a42..416f52ab39ec 100644 > --- a/arch/x86/boot/compressed/Makefile > +++ b/arch/x86/boot/compressed/Makefile > @@ -32,7 +32,7 @@ KBUILD_CFLAGS := -m$(BITS) -O2 > KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC) > KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING > cflags-$(CONFIG_X86_32) := -march=i386 > -cflags-$(CONFIG_X86_64) := -mcmodel=small > +cflags-$(CONFIG_X86_64) := -mcmodel=small -mno-red-zone > KBUILD_CFLAGS += $(cflags-y) > KBUILD_CFLAGS += -mno-mmx -mno-sse > KBUILD_CFLAGS += $(call cc-option,-ffreestanding) > -- > 2.27.0 > This one is necessary.
