Re: [PATCH 4/4] arm64: drop binutils version checks

[Mark Rutland]

Hi Arnd,

On Mon, Apr 07, 2025 at 11:41:16AM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> Now that gcc-8 and binutils-2.30 are the minimum versions, a lot of
> the individual feature checks can go away for simplification.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

To address Will's concern, I grabbed the LLVM 13.0.1 (since that's the
minimum supported version) from https://www.kernel.org/pub//tools/llvm/,
and using v6.15-rc1 I checked the Kconfig resulting from:

  # magic script that puts the toolchain in my $PATH
  usekorg-llvm 13.0.1 make ARCH=arm64 LLVM=1 defconfig
  usekorg-llvm 13.0.1 make ARCH=arm64 LLVM=1 menuconfig

I then applied this series, and built a defconfig kernel with the same
toolchain, which built cleanly and boots fine.

The gist is that everything looks good, so:

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>

More specifically, with that I see:

	CC_IS_CLANG [=y]
	AS_IS_LLVM [=y]
	LD_IS_LLD [=y]

... and I've noted each of the Kconfig options below.

[...]

> -config ARM64_LD_HAS_FIX_ERRATUM_843419
> -	def_bool $(ld-option,--fix-cortex-a53-843419)

	ARM64_LD_HAS_FIX_ERRATUM_843419 [=y] 

> -config AS_HAS_LSE_ATOMICS
> -	def_bool $(as-instr,.arch_extension lse)

	AS_HAS_LSE_ATOMICS [=y]

> -config AS_HAS_ARMV8_2
> -	def_bool $(cc-option,-Wa$(comma)-march=armv8.2-a)

	AS_HAS_ARMV8_2 [=y]

> -config AS_HAS_SHA3
> -	def_bool $(as-instr,.arch armv8.2-a+sha3)

	AS_HAS_SHA3 [=y]

> -config CC_HAS_SIGN_RETURN_ADDRESS
> -	# GCC 7, 8
> -	def_bool $(cc-option,-msign-return-address=all)

	 CC_HAS_SIGN_RETURN_ADDRESS [=y]

> -config AS_HAS_ARMV8_3
> -	def_bool $(cc-option,-Wa$(comma)-march=armv8.3-a)

	AS_HAS_ARMV8_3 [=y]

>  config AS_HAS_CFI_NEGATE_RA_STATE
> +	# binutils 2.34+
>  	def_bool $(as-instr,.cfi_startproc\n.cfi_negate_ra_state\n.cfi_endproc\n)

	AS_HAS_CFI_NEGATE_RA_STATE [=y]

> -config AS_HAS_LDAPR
> -	def_bool $(as-instr,.arch_extension rcpc)

	AS_HAS_LDAPR [=y]

> -config AS_HAS_ARMV8_4
> -	def_bool $(cc-option,-Wa$(comma)-march=armv8.4-a)

	AS_HAS_ARMV8_4 [=y]

> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 1d5dfcd1c13e..73a10f65ce8b 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -16,14 +16,11 @@ ifeq ($(CONFIG_RELOCATABLE), y)
>  # Pass --no-apply-dynamic-relocs to restore pre-binutils-2.27 behaviour
>  # for relative relocs, since this leads to better Image compression
>  # with the relocation offsets always being zero.
> -LDFLAGS_vmlinux		+= -shared -Bsymbolic -z notext \
> -			$(call ld-option, --no-apply-dynamic-relocs)
> +LDFLAGS_vmlinux	+= -shared -Bsymbolic -z notext --no-apply-dynamic-relocs
>  endif

Looks good:

  [mark@lakrids:~/src/linux]% usekorg-llvm 13.0.1 ld.lld -shared -Bsymbolic -z notext --made-up-argument       
  ld.lld: error: unknown argument '--made-up-argument'
  [mark@lakrids:~/src/linux]% usekorg-llvm 13.0.1 ld.lld -shared -Bsymbolic -z notext --no-apply-dynamic-relocs
  ld.lld: error: no input files

>  ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
> -  ifeq ($(CONFIG_ARM64_LD_HAS_FIX_ERRATUM_843419),y)
>  LDFLAGS_vmlinux	+= --fix-cortex-a53-843419
> -  endif
>  endif

Looks good:

  [mark@lakrids:~/src/linux]% usekorg-llvm 13.0.1 ld.lld --made-up-argument
  ld.lld: error: unknown argument '--made-up-argument'
  [mark@lakrids:~/src/linux]% usekorg-llvm 13.0.1 ld.lld --fix-cortex-a53-843419
  ld.lld: error: no input files

[...]

>  ifeq ($(CONFIG_AS_HAS_ARMV8_5), y)
>    asm-arch := armv8.5-a
> -else ifeq ($(CONFIG_AS_HAS_ARMV8_4), y)
> +else
>    asm-arch := armv8.4-a
> -else ifeq ($(CONFIG_AS_HAS_ARMV8_3), y)
> -  asm-arch := armv8.3-a
> -else ifeq ($(CONFIG_AS_HAS_ARMV8_2), y)
> -  asm-arch := armv8.2-a
>  endif

Looks good; this was checked in Kconfig.

[...]

>  archprepare:
>  	$(Q)$(MAKE) $(build)=arch/arm64/tools kapi
> -ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
> -  ifneq ($(CONFIG_ARM64_LD_HAS_FIX_ERRATUM_843419),y)
> -	@echo "warning: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum" >&2
> -  endif
> -endif
> -ifeq ($(CONFIG_ARM64_USE_LSE_ATOMICS),y)
> -  ifneq ($(CONFIG_ARM64_LSE_ATOMICS),y)
> -	@echo "warning: LSE atomics not supported by binutils" >&2
> -  endif
> -endif

Looks good; both were checked in Kconfig.

[...]

> -#ifdef CONFIG_AS_HAS_LDAPR
>  #define __LOAD_RCPC(sfx, regs...)					\
>  	ALTERNATIVE(							\
>  		"ldar"	#sfx "\t" #regs,				\
>  		".arch_extension rcpc\n"				\
>  		"ldapr"	#sfx "\t" #regs,				\
>  	ARM64_HAS_LDAPR)
> -#else
> -#define __LOAD_RCPC(sfx, regs...)	"ldar" #sfx "\t" #regs
> -#endif /* CONFIG_AS_HAS_LDAPR */

Looks good.

>  
>  /*
>   * When building with LTO, there is an increased risk of the compiler
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 096e45acadb2..713248f240e0 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -19,7 +19,6 @@ if VIRTUALIZATION
>  
>  menuconfig KVM
>  	bool "Kernel-based Virtual Machine (KVM) support"
> -	depends on AS_HAS_ARMV8_4
>  	select KVM_COMMON
>  	select KVM_GENERIC_HARDWARE_ENABLING
>  	select KVM_GENERIC_MMU_NOTIFIER

Looks good.

> diff --git a/arch/arm64/lib/xor-neon.c b/arch/arm64/lib/xor-neon.c
> index f9a53b7f9842..8fffebfa17b2 100644
> --- a/arch/arm64/lib/xor-neon.c
> +++ b/arch/arm64/lib/xor-neon.c
> @@ -319,7 +319,7 @@ static void xor_arm64_eor3_5(unsigned long bytes,
>  
>  static int __init xor_neon_init(void)
>  {
> -	if (IS_ENABLED(CONFIG_AS_HAS_SHA3) && cpu_have_named_feature(SHA3)) {
> +	if (cpu_have_named_feature(SHA3)) {

Looks good.

Mark.