linux/arch/arm/Kconfig.assembler

# SPDX-License-Identifier: GPL-2.0

config AS_VFP_VMRS_FPINST
	def_bool $(as-instr,.fpu vfpv2\nvmrs r0$(comma)FPINST)
	help
	  Supported by binutils >= 2.24 and LLVM integrated assembler.
ARM: 8991/1: use VFP assembler mnemonics if available The integrated assembler of Clang 10 and earlier do not allow to access the VFP registers through the coprocessor load/store instructions: arch/arm/vfp/vfpmodule.c:342:2: error: invalid operand for instruction fmxr(FPEXC, fpexc & ~(FPEXC_EX\|FPEXC_DEX\|FPEXC_FP2V\|FPEXC_VV\|FPEXC_TRAP_MASK)); ^ arch/arm/vfp/vfpinstr.h:79:6: note: expanded from macro 'fmxr' asm("mcr p10, 7, %0, " vfpreg(_vfp_) ", cr0, 0 @ fmxr " #_vfp_ ", %0" ^ <inline asm>:1:6: note: instantiated into assembly here mcr p10, 7, r0, cr8, cr0, 0 @ fmxr FPEXC, r0 ^ This has been addressed with Clang 11 [0]. However, to support earlier versions of Clang and for better readability use of VFP assembler mnemonics still is preferred. Ideally we would replace this code with the unified assembler language mnemonics vmrs/vmsr on call sites along with .fpu assembler directives. The GNU assembler supports the .fpu directive at least since 2.17 (when documentation has been added). Since Linux requires binutils 2.21 it is safe to use .fpu directive. However, binutils does not allow to use FPINST or FPINST2 as an argument to vmrs/vmsr instructions up to binutils 2.24 (see binutils commit 16d02dc907c5): arch/arm/vfp/vfphw.S: Assembler messages: arch/arm/vfp/vfphw.S:162: Error: operand 0 must be FPSID or FPSCR pr FPEXC -- `vmsr FPINST,r6' arch/arm/vfp/vfphw.S:165: Error: operand 0 must be FPSID or FPSCR pr FPEXC -- `vmsr FPINST2,r8' arch/arm/vfp/vfphw.S:235: Error: operand 1 must be a VFP extension System Register -- `vmrs r3,FPINST' arch/arm/vfp/vfphw.S:238: Error: operand 1 must be a VFP extension System Register -- `vmrs r12,FPINST2' Use as-instr in Kconfig to check if FPINST/FPINST2 can be used. If they can be used make use of .fpu directives and UAL VFP mnemonics for register access. This allows to build vfpmodule.c with Clang and its integrated assembler. [0] https://reviews.llvm.org/D59733 Link: https://github.com/ClangBuiltLinux/linux/issues/905 Signed-off-by: Stefan Agner <stefan@agner.ch> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk> 2020-07-09 18:21:27 +08:00			`# SPDX-License-Identifier: GPL-2.0`

			`config AS_VFP_VMRS_FPINST`
			`def_bool $(as-instr,.fpu vfpv2\nvmrs r0$(comma)FPINST)`
			`help`
			`Supported by binutils >= 2.24 and LLVM integrated assembler.`