On Mon, Oct 24, 2022 at 08:57:13AM +0200, Ahmad Fatoum wrote: > Recent episode with pointer authentication showed again that for > platforms without __attribute__((naked)), we are better off writing > the early header in assembly. We still want to keep the board specific > entry points in C for ease of use, so we have ENTRY_FUNCTION_WITHSTACK > generate two symbols: > > - A 32-bit stack top value that's placed in .rodata > > - An entry point with the normal C code, including stack-using > prologues > > The new common assembly head code will access the stack pointer in a > position-independent manner and set it up, before continuing with the > C code. The barebox header is part of the common assembly head code > ensuring it's not moved around due to compiler code generation. > > The common code will need access to board-specific entry point and stack > top. The former is readily available as the alias __pbl_board_entry. > The latter is a bit more complicated, as the symbol may not exist for > boards not using the common header in a multi-image build. > > Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> > --- > Makefile | 3 +-- > arch/arm/cpu/Makefile | 2 ++ > arch/arm/cpu/head_64.S | 36 ++++++++++++++++++++++++++++++ > arch/arm/include/asm/barebox-arm.h | 28 +++++++---------------- > arch/arm/lib/pbl.lds.S | 9 ++++++++ > 5 files changed, 56 insertions(+), 22 deletions(-) > create mode 100644 arch/arm/cpu/head_64.S > > diff --git a/Makefile b/Makefile > index 81ef44122367..a4b9f3c021d7 100644 > --- a/Makefile > +++ b/Makefile > @@ -660,8 +660,7 @@ KBUILD_CFLAGS += $(call cc-option,-fno-stack-check) > KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none) > > # We don't have the necessary infrastructure to benefit from ARMv8.3+ pointer > -# authentication. On older CPUs, they are interpreted as NOPs and blot the > -# code and break less portable code that expects a very specific code layout > +# authentication. On older CPUs, they are interpreted as NOPs bloating the code > KBUILD_CFLAGS += $(call cc-option,-mbranch-protection=none) > > KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > diff --git a/arch/arm/cpu/Makefile b/arch/arm/cpu/Makefile > index c0993c1abe5d..7674c1464c1f 100644 > --- a/arch/arm/cpu/Makefile > +++ b/arch/arm/cpu/Makefile > @@ -13,6 +13,8 @@ AFLAGS_hyp.pbl.o :=-Wa,-march=armv7-a -Wa,-mcpu=all > obj-y += start.o entry.o entry_ll$(S64).o > KASAN_SANITIZE_start.o := n > > +pbl-$(CONFIG_CPU_64) += head_64.o > + > pbl-$(CONFIG_BOARD_ARM_GENERIC_DT) += board-dt-2nd.o > pbl-$(CONFIG_BOARD_ARM_GENERIC_DT_AARCH64) += board-dt-2nd-aarch64.o > > diff --git a/arch/arm/cpu/head_64.S b/arch/arm/cpu/head_64.S > new file mode 100644 > index 000000000000..4ed4ffb05250 > --- /dev/null > +++ b/arch/arm/cpu/head_64.S > @@ -0,0 +1,36 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > +#include <linux/linkage.h> > +#include <asm/barebox-arm64.h> > +#include <asm/image.h> > + > +/* Linker will point these at board-specific symbols */ > +.globl __pbl_board_stack_top > +.globl __pbl_board_entry > + > +.section .text_head_prologue_common, "x" > +ENTRY(__barebox_arm64_head) > + nop > + nop > + nop Why these nops here? > + adr x9, __pbl_board_stack_top > + ldr w9, [x9] > + cbz x9, 1f > + mov sp, x9 > + b 1f > + .org 0x20 > + .asciz "barebox" > + .word 0xffffffff > + .word _barebox_image_size /* image size to copy */ > + .rept 8 > + .word 0x55555555 > + .endr > +1: > +#ifdef CONFIG_PBL_BREAK > + brk #17 > + nop > +#else > + nop > + nop > +#endif Why do you jump over the barebox header? You could put all the code before it. Sascha -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
