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* [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO
@ 2022-08-19 17:00 Nick Desaulniers
  2022-08-19 17:11 ` Borislav Petkov
                   ` (2 more replies)
  0 siblings, 3 replies; 13+ messages in thread
From: Nick Desaulniers @ 2022-08-19 17:00 UTC (permalink / raw)
  To: Masahiro Yamada
  Cc: Peter Zijlstra, x86, linux-kbuild, linux-doc, linux-kernel,
	linux-um, kvm, llvm, Linus Torvalds, Nick Desaulniers,
	Alexandre Belloni

GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
The minimum supported versions of these tools for the build according to
Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.

Remove the feature detection script, Kconfig option, and clean up some
fallback code that is no longer supported.

The removed script was also testing for a GCC specific bug that was
fixed in the 4.7 release.

The script was also not portable; users of Dash shell reported errors
when it was invoked.

Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
Reported-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Documentation/kbuild/kconfig-language.rst |  4 ++--
 arch/Kconfig                              |  3 +--
 arch/um/include/asm/cpufeature.h          |  4 ++--
 arch/x86/Makefile                         |  4 ----
 arch/x86/include/asm/cpufeature.h         |  4 ++--
 arch/x86/include/asm/rmwcc.h              | 19 +------------------
 arch/x86/kvm/emulate.c                    |  2 +-
 init/Kconfig                              |  4 ----
 scripts/gcc-goto.sh                       | 22 ----------------------
 tools/arch/x86/include/asm/rmwcc.h        | 21 ---------------------
 10 files changed, 9 insertions(+), 78 deletions(-)
 delete mode 100755 scripts/gcc-goto.sh

diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
index 7fb398649f51..858ed5d80def 100644
--- a/Documentation/kbuild/kconfig-language.rst
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -525,8 +525,8 @@ followed by a test macro::
 If you need to expose a compiler capability to makefiles and/or C source files,
 `CC_HAS_` is the recommended prefix for the config option::
 
-  config CC_HAS_ASM_GOTO
-	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
+  config CC_HAS_FOO
+	def_bool $(success,$(srctree)/scripts/cc-check-foo.sh $(CC))
 
 Build as module only
 ~~~~~~~~~~~~~~~~~~~~
diff --git a/arch/Kconfig b/arch/Kconfig
index f330410da63a..5dbf11a5ba4e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -53,7 +53,6 @@ config KPROBES
 config JUMP_LABEL
 	bool "Optimize very unlikely/likely branches"
 	depends on HAVE_ARCH_JUMP_LABEL
-	depends on CC_HAS_ASM_GOTO
 	select OBJTOOL if HAVE_JUMP_LABEL_HACK
 	help
 	 This option enables a transparent branch optimization that
@@ -1361,7 +1360,7 @@ config HAVE_PREEMPT_DYNAMIC_CALL
 
 config HAVE_PREEMPT_DYNAMIC_KEY
 	bool
-	depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
+	depends on HAVE_ARCH_JUMP_LABEL
 	select HAVE_PREEMPT_DYNAMIC
 	help
 	   An architecture should select this if it can handle the preemption
diff --git a/arch/um/include/asm/cpufeature.h b/arch/um/include/asm/cpufeature.h
index 19cd7ed6ec3c..94ff93ce20de 100644
--- a/arch/um/include/asm/cpufeature.h
+++ b/arch/um/include/asm/cpufeature.h
@@ -65,11 +65,11 @@ extern void setup_clear_cpu_cap(unsigned int bit);
 
 #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
 
-#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
+#if defined(__clang__) && __clang_major__ < 9
 
 /*
  * Workaround for the sake of BPF compilation which utilizes kernel
- * headers, but clang does not support ASM GOTO and fails the build.
+ * headers, but clang < 9 does not support ASM GOTO and fails the build.
  */
 #ifndef __BPF_TRACING__
 #warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 7854685c5f25..bafbd905e6e7 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -286,10 +286,6 @@ vdso_install:
 
 archprepare: checkbin
 checkbin:
-ifndef CONFIG_CC_HAS_ASM_GOTO
-	@echo Compiler lacks asm-goto support.
-	@exit 1
-endif
 ifdef CONFIG_RETPOLINE
 ifeq ($(RETPOLINE_CFLAGS),)
 	@echo "You are building kernel with non-retpoline compiler." >&2
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index ea34cc31b047..29951da819ca 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -155,11 +155,11 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
 
 #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
 
-#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
+#if defined(__clang__) && __clang_major__ < 9
 
 /*
  * Workaround for the sake of BPF compilation which utilizes kernel
- * headers, but clang does not support ASM GOTO and fails the build.
+ * headers, but clang < 9 does not support ASM GOTO and fails the build.
  */
 #ifndef __BPF_TRACING__
 #warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
index 8a9eba191516..c82f1b334207 100644
--- a/arch/x86/include/asm/rmwcc.h
+++ b/arch/x86/include/asm/rmwcc.h
@@ -11,9 +11,7 @@
 
 #define __CLOBBERS_MEM(clb...)	"memory", ## clb
 
-#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CONFIG_CC_HAS_ASM_GOTO)
-
-/* Use asm goto */
+#ifndef __GCC_ASM_FLAG_OUTPUTS__
 
 #define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)			\
 ({									\
@@ -27,21 +25,6 @@ cc_label:	c = true;						\
 	c;								\
 })
 
-#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
-
-/* Use flags output or a set instruction */
-
-#define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)			\
-({									\
-	bool c;								\
-	asm volatile (fullop CC_SET(cc)					\
-			: [var] "+m" (_var), CC_OUT(cc) (c)		\
-			: __VA_ARGS__ : clobbers);			\
-	c;								\
-})
-
-#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
-
 #define GEN_UNARY_RMWcc_4(op, var, cc, arg0)				\
 	__GEN_RMWcc(op " " arg0, var, cc, __CLOBBERS_MEM())
 
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b4eeb7c75dfa..08613c65138d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -493,7 +493,7 @@ FOP_END;
 
 /*
  * XXX: inoutclob user must know where the argument is being expanded.
- *      Relying on CONFIG_CC_HAS_ASM_GOTO would allow us to remove _fault.
+ *      Using asm goto would allow us to remove _fault.
  */
 #define asm_safe(insn, inoutclob...) \
 ({ \
diff --git a/init/Kconfig b/init/Kconfig
index 80fe60fa77fb..532362fcfe31 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -70,11 +70,7 @@ config CC_CAN_LINK_STATIC
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
 
-config CC_HAS_ASM_GOTO
-	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
-
 config CC_HAS_ASM_GOTO_OUTPUT
-	depends on CC_HAS_ASM_GOTO
 	def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
 
 config CC_HAS_ASM_GOTO_TIED_OUTPUT
diff --git a/scripts/gcc-goto.sh b/scripts/gcc-goto.sh
deleted file mode 100755
index 8b980fb2270a..000000000000
--- a/scripts/gcc-goto.sh
+++ /dev/null
@@ -1,22 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-# Test for gcc 'asm goto' support
-# Copyright (C) 2010, Jason Baron <jbaron@redhat.com>
-
-cat << "END" | $@ -x c - -fno-PIE -c -o /dev/null
-int main(void)
-{
-#if defined(__arm__) || defined(__aarch64__)
-	/*
-	 * Not related to asm goto, but used by jump label
-	 * and broken on some ARM GCC versions (see GCC Bug 48637).
-	 */
-	static struct { int dummy; int state; } tp;
-	asm (".long %c0" :: "i" (&tp.state));
-#endif
-
-entry:
-	asm goto ("" :::: entry);
-	return 0;
-}
-END
diff --git a/tools/arch/x86/include/asm/rmwcc.h b/tools/arch/x86/include/asm/rmwcc.h
index fee7983a90b4..11ff975242ca 100644
--- a/tools/arch/x86/include/asm/rmwcc.h
+++ b/tools/arch/x86/include/asm/rmwcc.h
@@ -2,8 +2,6 @@
 #ifndef _TOOLS_LINUX_ASM_X86_RMWcc
 #define _TOOLS_LINUX_ASM_X86_RMWcc
 
-#ifdef CONFIG_CC_HAS_ASM_GOTO
-
 #define __GEN_RMWcc(fullop, var, cc, ...)				\
 do {									\
 	asm_volatile_goto (fullop "; j" cc " %l[cc_label]"		\
@@ -20,23 +18,4 @@ cc_label:								\
 #define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
 	__GEN_RMWcc(op " %1, " arg0, var, cc, vcon (val))
 
-#else /* !CONFIG_CC_HAS_ASM_GOTO */
-
-#define __GEN_RMWcc(fullop, var, cc, ...)				\
-do {									\
-	char c;								\
-	asm volatile (fullop "; set" cc " %1"				\
-			: "+m" (var), "=qm" (c)				\
-			: __VA_ARGS__ : "memory");			\
-	return c != 0;							\
-} while (0)
-
-#define GEN_UNARY_RMWcc(op, var, arg0, cc)				\
-	__GEN_RMWcc(op " " arg0, var, cc)
-
-#define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
-	__GEN_RMWcc(op " %2, " arg0, var, cc, vcon (val))
-
-#endif /* CONFIG_CC_HAS_ASM_GOTO */
-
 #endif /* _TOOLS_LINUX_ASM_X86_RMWcc */
-- 
2.37.1.595.g718a3a8f04-goog


^ permalink raw reply related	[flat|nested] 13+ messages in thread
* Re: [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO
  2022-08-19 17:00 [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO Nick Desaulniers
@ 2022-08-19 17:11 ` Borislav Petkov
  2022-08-19 17:16 ` Alexandre Belloni
  2022-08-19 18:45 ` [PATCH] Kconfig: " Nick Desaulniers
  2 siblings, 0 replies; 13+ messages in thread
From: Borislav Petkov @ 2022-08-19 17:11 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Masahiro Yamada, Peter Zijlstra, x86, linux-kbuild, linux-doc,
	linux-kernel, linux-um, kvm, llvm, Linus Torvalds,
	Alexandre Belloni

On Fri, Aug 19, 2022 at 10:00:53AM -0700, Nick Desaulniers wrote:
> GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> The minimum supported versions of these tools for the build according to
> Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> 
> Remove the feature detection script, Kconfig option, and clean up some
> fallback code that is no longer supported.
> 
> The removed script was also testing for a GCC specific bug that was
> fixed in the 4.7 release.
> 
> The script was also not portable; users of Dash shell reported errors
> when it was invoked.
> 
> Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
> Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
> Reported-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
>  Documentation/kbuild/kconfig-language.rst |  4 ++--
>  arch/Kconfig                              |  3 +--
>  arch/um/include/asm/cpufeature.h          |  4 ++--
>  arch/x86/Makefile                         |  4 ----
>  arch/x86/include/asm/cpufeature.h         |  4 ++--
>  arch/x86/include/asm/rmwcc.h              | 19 +------------------
>  arch/x86/kvm/emulate.c                    |  2 +-
>  init/Kconfig                              |  4 ----
>  scripts/gcc-goto.sh                       | 22 ----------------------
>  tools/arch/x86/include/asm/rmwcc.h        | 21 ---------------------
>  10 files changed, 9 insertions(+), 78 deletions(-)
>  delete mode 100755 scripts/gcc-goto.sh

Nice and good riddance.

Acked-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO
  2022-08-19 17:00 [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO Nick Desaulniers
  2022-08-19 17:11 ` Borislav Petkov
@ 2022-08-19 17:16 ` Alexandre Belloni
  2022-08-19 17:28   ` Nick Desaulniers
  2022-08-19 18:45 ` [PATCH] Kconfig: " Nick Desaulniers
  2 siblings, 1 reply; 13+ messages in thread
From: Alexandre Belloni @ 2022-08-19 17:16 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Masahiro Yamada, Peter Zijlstra, x86, linux-kbuild, linux-doc,
	linux-kernel, linux-um, kvm, llvm, Linus Torvalds

On 19/08/2022 10:00:53-0700, Nick Desaulniers wrote:
> GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> The minimum supported versions of these tools for the build according to
> Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> 
> Remove the feature detection script, Kconfig option, and clean up some
> fallback code that is no longer supported.
> 
> The removed script was also testing for a GCC specific bug that was
> fixed in the 4.7 release.
> 
> The script was also not portable; users of Dash shell reported errors
> when it was invoked.
> 

To be clear, the script was portable, what is not working with dash is
the current detection of CC_HAS_ASM_GOTO_TIED_OUTPUT. I'll try the other
suggestion from Masahiro.

> Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
> Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
> Reported-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
>  Documentation/kbuild/kconfig-language.rst |  4 ++--
>  arch/Kconfig                              |  3 +--
>  arch/um/include/asm/cpufeature.h          |  4 ++--
>  arch/x86/Makefile                         |  4 ----
>  arch/x86/include/asm/cpufeature.h         |  4 ++--
>  arch/x86/include/asm/rmwcc.h              | 19 +------------------
>  arch/x86/kvm/emulate.c                    |  2 +-
>  init/Kconfig                              |  4 ----
>  scripts/gcc-goto.sh                       | 22 ----------------------
>  tools/arch/x86/include/asm/rmwcc.h        | 21 ---------------------
>  10 files changed, 9 insertions(+), 78 deletions(-)
>  delete mode 100755 scripts/gcc-goto.sh
> 
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index 7fb398649f51..858ed5d80def 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -525,8 +525,8 @@ followed by a test macro::
>  If you need to expose a compiler capability to makefiles and/or C source files,
>  `CC_HAS_` is the recommended prefix for the config option::
>  
> -  config CC_HAS_ASM_GOTO
> -	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> +  config CC_HAS_FOO
> +	def_bool $(success,$(srctree)/scripts/cc-check-foo.sh $(CC))
>  
>  Build as module only
>  ~~~~~~~~~~~~~~~~~~~~
> diff --git a/arch/Kconfig b/arch/Kconfig
> index f330410da63a..5dbf11a5ba4e 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -53,7 +53,6 @@ config KPROBES
>  config JUMP_LABEL
>  	bool "Optimize very unlikely/likely branches"
>  	depends on HAVE_ARCH_JUMP_LABEL
> -	depends on CC_HAS_ASM_GOTO
>  	select OBJTOOL if HAVE_JUMP_LABEL_HACK
>  	help
>  	 This option enables a transparent branch optimization that
> @@ -1361,7 +1360,7 @@ config HAVE_PREEMPT_DYNAMIC_CALL
>  
>  config HAVE_PREEMPT_DYNAMIC_KEY
>  	bool
> -	depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
> +	depends on HAVE_ARCH_JUMP_LABEL
>  	select HAVE_PREEMPT_DYNAMIC
>  	help
>  	   An architecture should select this if it can handle the preemption
> diff --git a/arch/um/include/asm/cpufeature.h b/arch/um/include/asm/cpufeature.h
> index 19cd7ed6ec3c..94ff93ce20de 100644
> --- a/arch/um/include/asm/cpufeature.h
> +++ b/arch/um/include/asm/cpufeature.h
> @@ -65,11 +65,11 @@ extern void setup_clear_cpu_cap(unsigned int bit);
>  
>  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
>  
> -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> +#if defined(__clang__) && __clang_major__ < 9
>  
>  /*
>   * Workaround for the sake of BPF compilation which utilizes kernel
> - * headers, but clang does not support ASM GOTO and fails the build.
> + * headers, but clang < 9 does not support ASM GOTO and fails the build.
>   */
>  #ifndef __BPF_TRACING__
>  #warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 7854685c5f25..bafbd905e6e7 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -286,10 +286,6 @@ vdso_install:
>  
>  archprepare: checkbin
>  checkbin:
> -ifndef CONFIG_CC_HAS_ASM_GOTO
> -	@echo Compiler lacks asm-goto support.
> -	@exit 1
> -endif
>  ifdef CONFIG_RETPOLINE
>  ifeq ($(RETPOLINE_CFLAGS),)
>  	@echo "You are building kernel with non-retpoline compiler." >&2
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index ea34cc31b047..29951da819ca 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -155,11 +155,11 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
>  
>  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
>  
> -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> +#if defined(__clang__) && __clang_major__ < 9

Shouldn't we simply mandates clang >= 9 and drop the whole section? This
is what you do later on.

>  
>  /*
>   * Workaround for the sake of BPF compilation which utilizes kernel
> - * headers, but clang does not support ASM GOTO and fails the build.
> + * headers, but clang < 9 does not support ASM GOTO and fails the build.
>   */
>  #ifndef __BPF_TRACING__
>  #warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
> diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
> index 8a9eba191516..c82f1b334207 100644
> --- a/arch/x86/include/asm/rmwcc.h
> +++ b/arch/x86/include/asm/rmwcc.h
> @@ -11,9 +11,7 @@
>  
>  #define __CLOBBERS_MEM(clb...)	"memory", ## clb
>  
> -#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CONFIG_CC_HAS_ASM_GOTO)
> -
> -/* Use asm goto */
> +#ifndef __GCC_ASM_FLAG_OUTPUTS__
>  
>  #define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)			\
>  ({									\
> @@ -27,21 +25,6 @@ cc_label:	c = true;						\
>  	c;								\
>  })
>  
> -#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> -
> -/* Use flags output or a set instruction */
> -
> -#define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)			\
> -({									\
> -	bool c;								\
> -	asm volatile (fullop CC_SET(cc)					\
> -			: [var] "+m" (_var), CC_OUT(cc) (c)		\
> -			: __VA_ARGS__ : clobbers);			\
> -	c;								\
> -})
> -
> -#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> -
>  #define GEN_UNARY_RMWcc_4(op, var, cc, arg0)				\
>  	__GEN_RMWcc(op " " arg0, var, cc, __CLOBBERS_MEM())
>  
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index b4eeb7c75dfa..08613c65138d 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -493,7 +493,7 @@ FOP_END;
>  
>  /*
>   * XXX: inoutclob user must know where the argument is being expanded.
> - *      Relying on CONFIG_CC_HAS_ASM_GOTO would allow us to remove _fault.
> + *      Using asm goto would allow us to remove _fault.
>   */
>  #define asm_safe(insn, inoutclob...) \
>  ({ \
> diff --git a/init/Kconfig b/init/Kconfig
> index 80fe60fa77fb..532362fcfe31 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -70,11 +70,7 @@ config CC_CAN_LINK_STATIC
>  	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
>  	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
>  
> -config CC_HAS_ASM_GOTO
> -	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> -
>  config CC_HAS_ASM_GOTO_OUTPUT
> -	depends on CC_HAS_ASM_GOTO
>  	def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
>  
>  config CC_HAS_ASM_GOTO_TIED_OUTPUT
> diff --git a/scripts/gcc-goto.sh b/scripts/gcc-goto.sh
> deleted file mode 100755
> index 8b980fb2270a..000000000000
> --- a/scripts/gcc-goto.sh
> +++ /dev/null
> @@ -1,22 +0,0 @@
> -#!/bin/sh
> -# SPDX-License-Identifier: GPL-2.0
> -# Test for gcc 'asm goto' support
> -# Copyright (C) 2010, Jason Baron <jbaron@redhat.com>
> -
> -cat << "END" | $@ -x c - -fno-PIE -c -o /dev/null
> -int main(void)
> -{
> -#if defined(__arm__) || defined(__aarch64__)
> -	/*
> -	 * Not related to asm goto, but used by jump label
> -	 * and broken on some ARM GCC versions (see GCC Bug 48637).
> -	 */
> -	static struct { int dummy; int state; } tp;
> -	asm (".long %c0" :: "i" (&tp.state));
> -#endif
> -
> -entry:
> -	asm goto ("" :::: entry);
> -	return 0;
> -}
> -END
> diff --git a/tools/arch/x86/include/asm/rmwcc.h b/tools/arch/x86/include/asm/rmwcc.h
> index fee7983a90b4..11ff975242ca 100644
> --- a/tools/arch/x86/include/asm/rmwcc.h
> +++ b/tools/arch/x86/include/asm/rmwcc.h
> @@ -2,8 +2,6 @@
>  #ifndef _TOOLS_LINUX_ASM_X86_RMWcc
>  #define _TOOLS_LINUX_ASM_X86_RMWcc
>  
> -#ifdef CONFIG_CC_HAS_ASM_GOTO
> -
>  #define __GEN_RMWcc(fullop, var, cc, ...)				\
>  do {									\
>  	asm_volatile_goto (fullop "; j" cc " %l[cc_label]"		\
> @@ -20,23 +18,4 @@ cc_label:								\
>  #define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
>  	__GEN_RMWcc(op " %1, " arg0, var, cc, vcon (val))
>  
> -#else /* !CONFIG_CC_HAS_ASM_GOTO */
> -
> -#define __GEN_RMWcc(fullop, var, cc, ...)				\
> -do {									\
> -	char c;								\
> -	asm volatile (fullop "; set" cc " %1"				\
> -			: "+m" (var), "=qm" (c)				\
> -			: __VA_ARGS__ : "memory");			\
> -	return c != 0;							\
> -} while (0)
> -
> -#define GEN_UNARY_RMWcc(op, var, arg0, cc)				\
> -	__GEN_RMWcc(op " " arg0, var, cc)
> -
> -#define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
> -	__GEN_RMWcc(op " %2, " arg0, var, cc, vcon (val))
> -
> -#endif /* CONFIG_CC_HAS_ASM_GOTO */
> -
>  #endif /* _TOOLS_LINUX_ASM_X86_RMWcc */
> -- 
> 2.37.1.595.g718a3a8f04-goog
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO
  2022-08-19 17:16 ` Alexandre Belloni
@ 2022-08-19 17:28   ` Nick Desaulniers
  2022-08-19 17:41     ` Masahiro Yamada
  0 siblings, 1 reply; 13+ messages in thread
From: Nick Desaulniers @ 2022-08-19 17:28 UTC (permalink / raw)
  To: Alexandre Belloni
  Cc: Masahiro Yamada, Peter Zijlstra, x86, linux-kbuild, linux-doc,
	linux-kernel, linux-um, kvm, llvm, Linus Torvalds,
	Alexei Starovoitov

On Fri, Aug 19, 2022 at 10:16 AM Alexandre Belloni
<alexandre.belloni@bootlin.com> wrote:
>
> On 19/08/2022 10:00:53-0700, Nick Desaulniers wrote:
> > GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> > The minimum supported versions of these tools for the build according to
> > Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> >
> > Remove the feature detection script, Kconfig option, and clean up some
> > fallback code that is no longer supported.
> >
> > The removed script was also testing for a GCC specific bug that was
> > fixed in the 4.7 release.
> >
> > The script was also not portable; users of Dash shell reported errors
> > when it was invoked.
> >
>
> To be clear, the script was portable, what is not working with dash is
> the current detection of CC_HAS_ASM_GOTO_TIED_OUTPUT. I'll try the other
> suggestion from Masahiro.

Ah, that was his point about echo; that makes more sense.

Unless a v2 is required, perhaps Masahiro would be kind enough to drop
this sentence from the commit message when applying?

>
> > --- a/arch/x86/include/asm/cpufeature.h
> > +++ b/arch/x86/include/asm/cpufeature.h
> > @@ -155,11 +155,11 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
> >
> >  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
> >
> > -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> > +#if defined(__clang__) && __clang_major__ < 9
>
> Shouldn't we simply mandates clang >= 9 and drop the whole section? This
> is what you do later on.

I considered it, but I don't think it would be safe to do so in this
header.  If you look at the comment block below it, it mentions that
these kernel headers are being sucked into UAPI headers that are used
outside of the kernel builds, such as when building eBPF programs.  So
we don't know what userspace tools might be consuming these headers.
The original intent of the guard was to not break eBPF compilation
with older clang releases, so I've retained. that functionality.

+ Alexei to review
(author of
commit b1ae32dbab50 ("x86/cpufeature: Guard asm_volatile_goto usage
for BPF compilation")
).
-- 
Thanks,
~Nick Desaulniers

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO
  2022-08-19 17:28   ` Nick Desaulniers
@ 2022-08-19 17:41     ` Masahiro Yamada
  2022-08-19 18:31       ` Alexei Starovoitov
  0 siblings, 1 reply; 13+ messages in thread
From: Masahiro Yamada @ 2022-08-19 17:41 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Alexandre Belloni, Peter Zijlstra, X86 ML,
	Linux Kbuild mailing list, open list:DOCUMENTATION,
	Linux Kernel Mailing List, linux-um, kvm, clang-built-linux,
	Linus Torvalds, Alexei Starovoitov

On Sat, Aug 20, 2022 at 2:28 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Aug 19, 2022 at 10:16 AM Alexandre Belloni
> <alexandre.belloni@bootlin.com> wrote:
> >
> > On 19/08/2022 10:00:53-0700, Nick Desaulniers wrote:
> > > GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> > > The minimum supported versions of these tools for the build according to
> > > Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> > >
> > > Remove the feature detection script, Kconfig option, and clean up some
> > > fallback code that is no longer supported.
> > >
> > > The removed script was also testing for a GCC specific bug that was
> > > fixed in the 4.7 release.
> > >
> > > The script was also not portable; users of Dash shell reported errors
> > > when it was invoked.
> > >
> >
> > To be clear, the script was portable, what is not working with dash is
> > the current detection of CC_HAS_ASM_GOTO_TIED_OUTPUT. I'll try the other
> > suggestion from Masahiro.
>
> Ah, that was his point about echo; that makes more sense.
>
> Unless a v2 is required, perhaps Masahiro would be kind enough to drop
> this sentence from the commit message when applying?

I can if there is nothing else to fix.


And, Alexandre's Reported-by is irrelevant.

As for the subject prefix "Kconfig:",
I prefer something else, for example,
"asm goto:" or "jump label:".

I want to reserve "Kconfig:" for changes in scripts/kconfig/.


>
> >
> > > --- a/arch/x86/include/asm/cpufeature.h
> > > +++ b/arch/x86/include/asm/cpufeature.h
> > > @@ -155,11 +155,11 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
> > >
> > >  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
> > >
> > > -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> > > +#if defined(__clang__) && __clang_major__ < 9
> >
> > Shouldn't we simply mandates clang >= 9 and drop the whole section? This
> > is what you do later on.
>
> I considered it, but I don't think it would be safe to do so in this
> header.  If you look at the comment block below it, it mentions that
> these kernel headers are being sucked into UAPI headers that are used
> outside of the kernel builds, such as when building eBPF programs.  So
> we don't know what userspace tools might be consuming these headers.
> The original intent of the guard was to not break eBPF compilation
> with older clang releases, so I've retained. that functionality.
>
> + Alexei to review
> (author of
> commit b1ae32dbab50 ("x86/cpufeature: Guard asm_volatile_goto usage
> for BPF compilation")


I am not sure at this point.
Wait for the input from Alexei.






> ).
> --
> Thanks,
> ~Nick Desaulniers



-- 
Best Regards
Masahiro Yamada

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO
  2022-08-19 17:41     ` Masahiro Yamada
@ 2022-08-19 18:31       ` Alexei Starovoitov
  2022-08-19 19:06         ` [PATCH v2] asm goto: " Nick Desaulniers
  0 siblings, 1 reply; 13+ messages in thread
From: Alexei Starovoitov @ 2022-08-19 18:31 UTC (permalink / raw)
  To: Masahiro Yamada
  Cc: Nick Desaulniers, Alexandre Belloni, Peter Zijlstra, X86 ML,
	Linux Kbuild mailing list, open list:DOCUMENTATION,
	Linux Kernel Mailing List, linux-um, kvm, clang-built-linux,
	Linus Torvalds, Alexei Starovoitov

On Fri, Aug 19, 2022 at 10:42 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Sat, Aug 20, 2022 at 2:28 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Fri, Aug 19, 2022 at 10:16 AM Alexandre Belloni
> > <alexandre.belloni@bootlin.com> wrote:
> > >
> > > On 19/08/2022 10:00:53-0700, Nick Desaulniers wrote:
> > > > GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> > > > The minimum supported versions of these tools for the build according to
> > > > Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> > > >
> > > > Remove the feature detection script, Kconfig option, and clean up some
> > > > fallback code that is no longer supported.
> > > >
> > > > The removed script was also testing for a GCC specific bug that was
> > > > fixed in the 4.7 release.
> > > >
> > > > The script was also not portable; users of Dash shell reported errors
> > > > when it was invoked.
> > > >
> > >
> > > To be clear, the script was portable, what is not working with dash is
> > > the current detection of CC_HAS_ASM_GOTO_TIED_OUTPUT. I'll try the other
> > > suggestion from Masahiro.
> >
> > Ah, that was his point about echo; that makes more sense.
> >
> > Unless a v2 is required, perhaps Masahiro would be kind enough to drop
> > this sentence from the commit message when applying?
>
> I can if there is nothing else to fix.
>
>
> And, Alexandre's Reported-by is irrelevant.
>
> As for the subject prefix "Kconfig:",
> I prefer something else, for example,
> "asm goto:" or "jump label:".
>
> I want to reserve "Kconfig:" for changes in scripts/kconfig/.
>
>
> >
> > >
> > > > --- a/arch/x86/include/asm/cpufeature.h
> > > > +++ b/arch/x86/include/asm/cpufeature.h
> > > > @@ -155,11 +155,11 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
> > > >
> > > >  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
> > > >
> > > > -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> > > > +#if defined(__clang__) && __clang_major__ < 9
> > >
> > > Shouldn't we simply mandates clang >= 9 and drop the whole section? This
> > > is what you do later on.
> >
> > I considered it, but I don't think it would be safe to do so in this
> > header.  If you look at the comment block below it, it mentions that
> > these kernel headers are being sucked into UAPI headers that are used
> > outside of the kernel builds, such as when building eBPF programs.  So
> > we don't know what userspace tools might be consuming these headers.
> > The original intent of the guard was to not break eBPF compilation
> > with older clang releases, so I've retained. that functionality.
> >
> > + Alexei to review
> > (author of
> > commit b1ae32dbab50 ("x86/cpufeature: Guard asm_volatile_goto usage
> > for BPF compilation")
>
>
> I am not sure at this point.
> Wait for the input from Alexei.

It's probably best to remove this old workaround.
bpftrace still has code that does:
  cflags.push_back("-D__BPF_TRACING__");
and bpftrace sort-of works with llvm 6+,
but they need to move to a newer clang for tons of other reasons
including lots of fixes in the clang bpf backend that were
added over the years.
So just nuke this old hack.

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO
  2022-08-19 17:00 [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO Nick Desaulniers
  2022-08-19 17:11 ` Borislav Petkov
  2022-08-19 17:16 ` Alexandre Belloni
@ 2022-08-19 18:45 ` Nick Desaulniers
  2 siblings, 0 replies; 13+ messages in thread
From: Nick Desaulniers @ 2022-08-19 18:45 UTC (permalink / raw)
  To: Masahiro Yamada
  Cc: Peter Zijlstra, x86, linux-kbuild, linux-doc, linux-kernel,
	linux-um, kvm, llvm, Linus Torvalds, Alexandre Belloni

On Fri, Aug 19, 2022 at 10:01 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
> index 8a9eba191516..c82f1b334207 100644
> --- a/arch/x86/include/asm/rmwcc.h
> +++ b/arch/x86/include/asm/rmwcc.h
> @@ -11,9 +11,7 @@
>
>  #define __CLOBBERS_MEM(clb...) "memory", ## clb
>
> -#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CONFIG_CC_HAS_ASM_GOTO)
> -
> -/* Use asm goto */
> +#ifndef __GCC_ASM_FLAG_OUTPUTS__
>
>  #define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)                   \
>  ({                                                                     \
> @@ -27,21 +25,6 @@ cc_label:    c = true;                                               \
>         c;                                                              \
>  })
>
> -#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> -
> -/* Use flags output or a set instruction */
> -
> -#define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)                   \
> -({                                                                     \
> -       bool c;                                                         \
> -       asm volatile (fullop CC_SET(cc)                                 \
> -                       : [var] "+m" (_var), CC_OUT(cc) (c)             \
> -                       : __VA_ARGS__ : clobbers);                      \
> -       c;                                                              \
> -})
> -
> -#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> -

^ probably don't want to remove the terminal endif. Will respin based
on feedback from Masahiro + Alexei.


-- 
Thanks,
~Nick Desaulniers

^ permalink raw reply	[flat|nested] 13+ messages in thread
* [PATCH v2] asm goto: eradicate CC_HAS_ASM_GOTO
  2022-08-19 18:31       ` Alexei Starovoitov
@ 2022-08-19 19:06         ` Nick Desaulniers
  2022-08-19 20:04           ` Alexandre Belloni
                             ` (3 more replies)
  0 siblings, 4 replies; 13+ messages in thread
From: Nick Desaulniers @ 2022-08-19 19:06 UTC (permalink / raw)
  To: Masahiro Yamada
  Cc: Peter Zijlstra, x86, linux-kbuild, linux-doc, linux-kernel,
	linux-um, kvm, llvm, Linus Torvalds, Alexandre Belloni,
	Nick Desaulniers, Borislav Petkov, Alexei Starovoitov

GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
The minimum supported versions of these tools for the build according to
Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.

Remove the feature detection script, Kconfig option, and clean up some
fallback code that is no longer supported.

The removed script was also testing for a GCC specific bug that was
fixed in the 4.7 release.

Also remove workarounds for bpftrace using clang older than 9.0.0, since
other BPF backend fixes are required at this point.

Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
Acked-by: Borislav Petkov <bp@suse.de>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---

Changes v1 -> v2:
https://lore.kernel.org/linux-kbuild/20220819170053.2686006-1-ndesaulniers@google.com/
* Pick up Boris' ack.
* Drop line about Dash compat as per Alexandre.
* Drop Alexandre's reported by as per Masahiro.
* s/Kbuild/asm goto/ in oneline as per Masahiro.
* Remove entirety of bpftrace workarounds as per Alexei.
* Fix mistake in arch/x86/include/asm/rmwcc.h in v1 where I removed too
  much; we still need guards for __GCC_ASM_FLAG_OUTPUTS__.

 Documentation/kbuild/kconfig-language.rst |  4 ++--
 arch/Kconfig                              |  3 +--
 arch/um/include/asm/cpufeature.h          | 15 ---------------
 arch/x86/Makefile                         |  4 ----
 arch/x86/include/asm/cpufeature.h         | 15 ---------------
 arch/x86/include/asm/rmwcc.h              |  6 +++---
 arch/x86/kvm/emulate.c                    |  2 +-
 init/Kconfig                              |  4 ----
 scripts/gcc-goto.sh                       | 22 ----------------------
 tools/arch/x86/include/asm/rmwcc.h        | 21 ---------------------
 10 files changed, 7 insertions(+), 89 deletions(-)
 delete mode 100755 scripts/gcc-goto.sh

diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
index 7fb398649f51..858ed5d80def 100644
--- a/Documentation/kbuild/kconfig-language.rst
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -525,8 +525,8 @@ followed by a test macro::
 If you need to expose a compiler capability to makefiles and/or C source files,
 `CC_HAS_` is the recommended prefix for the config option::
 
-  config CC_HAS_ASM_GOTO
-	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
+  config CC_HAS_FOO
+	def_bool $(success,$(srctree)/scripts/cc-check-foo.sh $(CC))
 
 Build as module only
 ~~~~~~~~~~~~~~~~~~~~
diff --git a/arch/Kconfig b/arch/Kconfig
index f330410da63a..5dbf11a5ba4e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -53,7 +53,6 @@ config KPROBES
 config JUMP_LABEL
 	bool "Optimize very unlikely/likely branches"
 	depends on HAVE_ARCH_JUMP_LABEL
-	depends on CC_HAS_ASM_GOTO
 	select OBJTOOL if HAVE_JUMP_LABEL_HACK
 	help
 	 This option enables a transparent branch optimization that
@@ -1361,7 +1360,7 @@ config HAVE_PREEMPT_DYNAMIC_CALL
 
 config HAVE_PREEMPT_DYNAMIC_KEY
 	bool
-	depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
+	depends on HAVE_ARCH_JUMP_LABEL
 	select HAVE_PREEMPT_DYNAMIC
 	help
 	   An architecture should select this if it can handle the preemption
diff --git a/arch/um/include/asm/cpufeature.h b/arch/um/include/asm/cpufeature.h
index 19cd7ed6ec3c..4b6d1b526bc1 100644
--- a/arch/um/include/asm/cpufeature.h
+++ b/arch/um/include/asm/cpufeature.h
@@ -65,20 +65,6 @@ extern void setup_clear_cpu_cap(unsigned int bit);
 
 #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
 
-#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
-
-/*
- * Workaround for the sake of BPF compilation which utilizes kernel
- * headers, but clang does not support ASM GOTO and fails the build.
- */
-#ifndef __BPF_TRACING__
-#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
-#endif
-
-#define static_cpu_has(bit)            boot_cpu_has(bit)
-
-#else
-
 /*
  * Static testing of CPU features. Used the same as boot_cpu_has(). It
  * statically patches the target code for additional performance. Use
@@ -137,7 +123,6 @@ static __always_inline bool _static_cpu_has(u16 bit)
 		boot_cpu_has(bit) :				\
 		_static_cpu_has(bit)				\
 )
-#endif
 
 #define cpu_has_bug(c, bit)		cpu_has(c, (bit))
 #define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 7854685c5f25..bafbd905e6e7 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -286,10 +286,6 @@ vdso_install:
 
 archprepare: checkbin
 checkbin:
-ifndef CONFIG_CC_HAS_ASM_GOTO
-	@echo Compiler lacks asm-goto support.
-	@exit 1
-endif
 ifdef CONFIG_RETPOLINE
 ifeq ($(RETPOLINE_CFLAGS),)
 	@echo "You are building kernel with non-retpoline compiler." >&2
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index ea34cc31b047..1a85e1fb0922 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -155,20 +155,6 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
 
 #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
 
-#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
-
-/*
- * Workaround for the sake of BPF compilation which utilizes kernel
- * headers, but clang does not support ASM GOTO and fails the build.
- */
-#ifndef __BPF_TRACING__
-#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
-#endif
-
-#define static_cpu_has(bit)            boot_cpu_has(bit)
-
-#else
-
 /*
  * Static testing of CPU features. Used the same as boot_cpu_has(). It
  * statically patches the target code for additional performance. Use
@@ -208,7 +194,6 @@ static __always_inline bool _static_cpu_has(u16 bit)
 		boot_cpu_has(bit) :				\
 		_static_cpu_has(bit)				\
 )
-#endif
 
 #define cpu_has_bug(c, bit)		cpu_has(c, (bit))
 #define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))
diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
index 8a9eba191516..7fa611216417 100644
--- a/arch/x86/include/asm/rmwcc.h
+++ b/arch/x86/include/asm/rmwcc.h
@@ -11,7 +11,7 @@
 
 #define __CLOBBERS_MEM(clb...)	"memory", ## clb
 
-#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CONFIG_CC_HAS_ASM_GOTO)
+#ifndef __GCC_ASM_FLAG_OUTPUTS__
 
 /* Use asm goto */
 
@@ -27,7 +27,7 @@ cc_label:	c = true;						\
 	c;								\
 })
 
-#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
+#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
 
 /* Use flags output or a set instruction */
 
@@ -40,7 +40,7 @@ cc_label:	c = true;						\
 	c;								\
 })
 
-#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
+#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
 
 #define GEN_UNARY_RMWcc_4(op, var, cc, arg0)				\
 	__GEN_RMWcc(op " " arg0, var, cc, __CLOBBERS_MEM())
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b4eeb7c75dfa..08613c65138d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -493,7 +493,7 @@ FOP_END;
 
 /*
  * XXX: inoutclob user must know where the argument is being expanded.
- *      Relying on CONFIG_CC_HAS_ASM_GOTO would allow us to remove _fault.
+ *      Using asm goto would allow us to remove _fault.
  */
 #define asm_safe(insn, inoutclob...) \
 ({ \
diff --git a/init/Kconfig b/init/Kconfig
index 80fe60fa77fb..532362fcfe31 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -70,11 +70,7 @@ config CC_CAN_LINK_STATIC
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
 
-config CC_HAS_ASM_GOTO
-	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
-
 config CC_HAS_ASM_GOTO_OUTPUT
-	depends on CC_HAS_ASM_GOTO
 	def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
 
 config CC_HAS_ASM_GOTO_TIED_OUTPUT
diff --git a/scripts/gcc-goto.sh b/scripts/gcc-goto.sh
deleted file mode 100755
index 8b980fb2270a..000000000000
--- a/scripts/gcc-goto.sh
+++ /dev/null
@@ -1,22 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-# Test for gcc 'asm goto' support
-# Copyright (C) 2010, Jason Baron <jbaron@redhat.com>
-
-cat << "END" | $@ -x c - -fno-PIE -c -o /dev/null
-int main(void)
-{
-#if defined(__arm__) || defined(__aarch64__)
-	/*
-	 * Not related to asm goto, but used by jump label
-	 * and broken on some ARM GCC versions (see GCC Bug 48637).
-	 */
-	static struct { int dummy; int state; } tp;
-	asm (".long %c0" :: "i" (&tp.state));
-#endif
-
-entry:
-	asm goto ("" :::: entry);
-	return 0;
-}
-END
diff --git a/tools/arch/x86/include/asm/rmwcc.h b/tools/arch/x86/include/asm/rmwcc.h
index fee7983a90b4..11ff975242ca 100644
--- a/tools/arch/x86/include/asm/rmwcc.h
+++ b/tools/arch/x86/include/asm/rmwcc.h
@@ -2,8 +2,6 @@
 #ifndef _TOOLS_LINUX_ASM_X86_RMWcc
 #define _TOOLS_LINUX_ASM_X86_RMWcc
 
-#ifdef CONFIG_CC_HAS_ASM_GOTO
-
 #define __GEN_RMWcc(fullop, var, cc, ...)				\
 do {									\
 	asm_volatile_goto (fullop "; j" cc " %l[cc_label]"		\
@@ -20,23 +18,4 @@ cc_label:								\
 #define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
 	__GEN_RMWcc(op " %1, " arg0, var, cc, vcon (val))
 
-#else /* !CONFIG_CC_HAS_ASM_GOTO */
-
-#define __GEN_RMWcc(fullop, var, cc, ...)				\
-do {									\
-	char c;								\
-	asm volatile (fullop "; set" cc " %1"				\
-			: "+m" (var), "=qm" (c)				\
-			: __VA_ARGS__ : "memory");			\
-	return c != 0;							\
-} while (0)
-
-#define GEN_UNARY_RMWcc(op, var, arg0, cc)				\
-	__GEN_RMWcc(op " " arg0, var, cc)
-
-#define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
-	__GEN_RMWcc(op " %2, " arg0, var, cc, vcon (val))
-
-#endif /* CONFIG_CC_HAS_ASM_GOTO */
-
 #endif /* _TOOLS_LINUX_ASM_X86_RMWcc */
-- 
2.37.1.595.g718a3a8f04-goog


^ permalink raw reply related	[flat|nested] 13+ messages in thread
* Re: [PATCH v2] asm goto: eradicate CC_HAS_ASM_GOTO
  2022-08-19 19:06         ` [PATCH v2] asm goto: " Nick Desaulniers
@ 2022-08-19 20:04           ` Alexandre Belloni
  2022-08-19 21:48           ` Nathan Chancellor
                             ` (2 subsequent siblings)
  3 siblings, 0 replies; 13+ messages in thread
From: Alexandre Belloni @ 2022-08-19 20:04 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Masahiro Yamada, Peter Zijlstra, x86, linux-kbuild, linux-doc,
	linux-kernel, linux-um, kvm, llvm, Linus Torvalds,
	Borislav Petkov, Alexei Starovoitov

On 19/08/2022 12:06:40-0700, Nick Desaulniers wrote:
> GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> The minimum supported versions of these tools for the build according to
> Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> 
> Remove the feature detection script, Kconfig option, and clean up some
> fallback code that is no longer supported.
> 
> The removed script was also testing for a GCC specific bug that was
> fixed in the 4.7 release.
> 
> Also remove workarounds for bpftrace using clang older than 9.0.0, since
> other BPF backend fixes are required at this point.
> 
> Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
> Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
> Acked-by: Borislav Petkov <bp@suse.de>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

> ---
> 
> Changes v1 -> v2:
> https://lore.kernel.org/linux-kbuild/20220819170053.2686006-1-ndesaulniers@google.com/
> * Pick up Boris' ack.
> * Drop line about Dash compat as per Alexandre.
> * Drop Alexandre's reported by as per Masahiro.
> * s/Kbuild/asm goto/ in oneline as per Masahiro.
> * Remove entirety of bpftrace workarounds as per Alexei.
> * Fix mistake in arch/x86/include/asm/rmwcc.h in v1 where I removed too
>   much; we still need guards for __GCC_ASM_FLAG_OUTPUTS__.
> 
>  Documentation/kbuild/kconfig-language.rst |  4 ++--
>  arch/Kconfig                              |  3 +--
>  arch/um/include/asm/cpufeature.h          | 15 ---------------
>  arch/x86/Makefile                         |  4 ----
>  arch/x86/include/asm/cpufeature.h         | 15 ---------------
>  arch/x86/include/asm/rmwcc.h              |  6 +++---
>  arch/x86/kvm/emulate.c                    |  2 +-
>  init/Kconfig                              |  4 ----
>  scripts/gcc-goto.sh                       | 22 ----------------------
>  tools/arch/x86/include/asm/rmwcc.h        | 21 ---------------------
>  10 files changed, 7 insertions(+), 89 deletions(-)
>  delete mode 100755 scripts/gcc-goto.sh
> 
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index 7fb398649f51..858ed5d80def 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -525,8 +525,8 @@ followed by a test macro::
>  If you need to expose a compiler capability to makefiles and/or C source files,
>  `CC_HAS_` is the recommended prefix for the config option::
>  
> -  config CC_HAS_ASM_GOTO
> -	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> +  config CC_HAS_FOO
> +	def_bool $(success,$(srctree)/scripts/cc-check-foo.sh $(CC))
>  
>  Build as module only
>  ~~~~~~~~~~~~~~~~~~~~
> diff --git a/arch/Kconfig b/arch/Kconfig
> index f330410da63a..5dbf11a5ba4e 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -53,7 +53,6 @@ config KPROBES
>  config JUMP_LABEL
>  	bool "Optimize very unlikely/likely branches"
>  	depends on HAVE_ARCH_JUMP_LABEL
> -	depends on CC_HAS_ASM_GOTO
>  	select OBJTOOL if HAVE_JUMP_LABEL_HACK
>  	help
>  	 This option enables a transparent branch optimization that
> @@ -1361,7 +1360,7 @@ config HAVE_PREEMPT_DYNAMIC_CALL
>  
>  config HAVE_PREEMPT_DYNAMIC_KEY
>  	bool
> -	depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
> +	depends on HAVE_ARCH_JUMP_LABEL
>  	select HAVE_PREEMPT_DYNAMIC
>  	help
>  	   An architecture should select this if it can handle the preemption
> diff --git a/arch/um/include/asm/cpufeature.h b/arch/um/include/asm/cpufeature.h
> index 19cd7ed6ec3c..4b6d1b526bc1 100644
> --- a/arch/um/include/asm/cpufeature.h
> +++ b/arch/um/include/asm/cpufeature.h
> @@ -65,20 +65,6 @@ extern void setup_clear_cpu_cap(unsigned int bit);
>  
>  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
>  
> -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> -
> -/*
> - * Workaround for the sake of BPF compilation which utilizes kernel
> - * headers, but clang does not support ASM GOTO and fails the build.
> - */
> -#ifndef __BPF_TRACING__
> -#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
> -#endif
> -
> -#define static_cpu_has(bit)            boot_cpu_has(bit)
> -
> -#else
> -
>  /*
>   * Static testing of CPU features. Used the same as boot_cpu_has(). It
>   * statically patches the target code for additional performance. Use
> @@ -137,7 +123,6 @@ static __always_inline bool _static_cpu_has(u16 bit)
>  		boot_cpu_has(bit) :				\
>  		_static_cpu_has(bit)				\
>  )
> -#endif
>  
>  #define cpu_has_bug(c, bit)		cpu_has(c, (bit))
>  #define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 7854685c5f25..bafbd905e6e7 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -286,10 +286,6 @@ vdso_install:
>  
>  archprepare: checkbin
>  checkbin:
> -ifndef CONFIG_CC_HAS_ASM_GOTO
> -	@echo Compiler lacks asm-goto support.
> -	@exit 1
> -endif
>  ifdef CONFIG_RETPOLINE
>  ifeq ($(RETPOLINE_CFLAGS),)
>  	@echo "You are building kernel with non-retpoline compiler." >&2
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index ea34cc31b047..1a85e1fb0922 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -155,20 +155,6 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
>  
>  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
>  
> -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> -
> -/*
> - * Workaround for the sake of BPF compilation which utilizes kernel
> - * headers, but clang does not support ASM GOTO and fails the build.
> - */
> -#ifndef __BPF_TRACING__
> -#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
> -#endif
> -
> -#define static_cpu_has(bit)            boot_cpu_has(bit)
> -
> -#else
> -
>  /*
>   * Static testing of CPU features. Used the same as boot_cpu_has(). It
>   * statically patches the target code for additional performance. Use
> @@ -208,7 +194,6 @@ static __always_inline bool _static_cpu_has(u16 bit)
>  		boot_cpu_has(bit) :				\
>  		_static_cpu_has(bit)				\
>  )
> -#endif
>  
>  #define cpu_has_bug(c, bit)		cpu_has(c, (bit))
>  #define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))
> diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
> index 8a9eba191516..7fa611216417 100644
> --- a/arch/x86/include/asm/rmwcc.h
> +++ b/arch/x86/include/asm/rmwcc.h
> @@ -11,7 +11,7 @@
>  
>  #define __CLOBBERS_MEM(clb...)	"memory", ## clb
>  
> -#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CONFIG_CC_HAS_ASM_GOTO)
> +#ifndef __GCC_ASM_FLAG_OUTPUTS__
>  
>  /* Use asm goto */
>  
> @@ -27,7 +27,7 @@ cc_label:	c = true;						\
>  	c;								\
>  })
>  
> -#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> +#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
>  
>  /* Use flags output or a set instruction */
>  
> @@ -40,7 +40,7 @@ cc_label:	c = true;						\
>  	c;								\
>  })
>  
> -#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> +#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
>  
>  #define GEN_UNARY_RMWcc_4(op, var, cc, arg0)				\
>  	__GEN_RMWcc(op " " arg0, var, cc, __CLOBBERS_MEM())
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index b4eeb7c75dfa..08613c65138d 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -493,7 +493,7 @@ FOP_END;
>  
>  /*
>   * XXX: inoutclob user must know where the argument is being expanded.
> - *      Relying on CONFIG_CC_HAS_ASM_GOTO would allow us to remove _fault.
> + *      Using asm goto would allow us to remove _fault.
>   */
>  #define asm_safe(insn, inoutclob...) \
>  ({ \
> diff --git a/init/Kconfig b/init/Kconfig
> index 80fe60fa77fb..532362fcfe31 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -70,11 +70,7 @@ config CC_CAN_LINK_STATIC
>  	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
>  	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
>  
> -config CC_HAS_ASM_GOTO
> -	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> -
>  config CC_HAS_ASM_GOTO_OUTPUT
> -	depends on CC_HAS_ASM_GOTO
>  	def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
>  
>  config CC_HAS_ASM_GOTO_TIED_OUTPUT
> diff --git a/scripts/gcc-goto.sh b/scripts/gcc-goto.sh
> deleted file mode 100755
> index 8b980fb2270a..000000000000
> --- a/scripts/gcc-goto.sh
> +++ /dev/null
> @@ -1,22 +0,0 @@
> -#!/bin/sh
> -# SPDX-License-Identifier: GPL-2.0
> -# Test for gcc 'asm goto' support
> -# Copyright (C) 2010, Jason Baron <jbaron@redhat.com>
> -
> -cat << "END" | $@ -x c - -fno-PIE -c -o /dev/null
> -int main(void)
> -{
> -#if defined(__arm__) || defined(__aarch64__)
> -	/*
> -	 * Not related to asm goto, but used by jump label
> -	 * and broken on some ARM GCC versions (see GCC Bug 48637).
> -	 */
> -	static struct { int dummy; int state; } tp;
> -	asm (".long %c0" :: "i" (&tp.state));
> -#endif
> -
> -entry:
> -	asm goto ("" :::: entry);
> -	return 0;
> -}
> -END
> diff --git a/tools/arch/x86/include/asm/rmwcc.h b/tools/arch/x86/include/asm/rmwcc.h
> index fee7983a90b4..11ff975242ca 100644
> --- a/tools/arch/x86/include/asm/rmwcc.h
> +++ b/tools/arch/x86/include/asm/rmwcc.h
> @@ -2,8 +2,6 @@
>  #ifndef _TOOLS_LINUX_ASM_X86_RMWcc
>  #define _TOOLS_LINUX_ASM_X86_RMWcc
>  
> -#ifdef CONFIG_CC_HAS_ASM_GOTO
> -
>  #define __GEN_RMWcc(fullop, var, cc, ...)				\
>  do {									\
>  	asm_volatile_goto (fullop "; j" cc " %l[cc_label]"		\
> @@ -20,23 +18,4 @@ cc_label:								\
>  #define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
>  	__GEN_RMWcc(op " %1, " arg0, var, cc, vcon (val))
>  
> -#else /* !CONFIG_CC_HAS_ASM_GOTO */
> -
> -#define __GEN_RMWcc(fullop, var, cc, ...)				\
> -do {									\
> -	char c;								\
> -	asm volatile (fullop "; set" cc " %1"				\
> -			: "+m" (var), "=qm" (c)				\
> -			: __VA_ARGS__ : "memory");			\
> -	return c != 0;							\
> -} while (0)
> -
> -#define GEN_UNARY_RMWcc(op, var, arg0, cc)				\
> -	__GEN_RMWcc(op " " arg0, var, cc)
> -
> -#define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
> -	__GEN_RMWcc(op " %2, " arg0, var, cc, vcon (val))
> -
> -#endif /* CONFIG_CC_HAS_ASM_GOTO */
> -
>  #endif /* _TOOLS_LINUX_ASM_X86_RMWcc */
> -- 
> 2.37.1.595.g718a3a8f04-goog
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH v2] asm goto: eradicate CC_HAS_ASM_GOTO
  2022-08-19 19:06         ` [PATCH v2] asm goto: " Nick Desaulniers
  2022-08-19 20:04           ` Alexandre Belloni
@ 2022-08-19 21:48           ` Nathan Chancellor
  2022-08-21 10:11           ` Ingo Molnar
  2022-08-21 17:11           ` Linus Torvalds
  3 siblings, 0 replies; 13+ messages in thread
From: Nathan Chancellor @ 2022-08-19 21:48 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Masahiro Yamada, Peter Zijlstra, x86, linux-kbuild, linux-doc,
	linux-kernel, linux-um, kvm, llvm, Linus Torvalds,
	Alexandre Belloni, Borislav Petkov, Alexei Starovoitov

On Fri, Aug 19, 2022 at 12:06:40PM -0700, Nick Desaulniers wrote:
> GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> The minimum supported versions of these tools for the build according to
> Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> 
> Remove the feature detection script, Kconfig option, and clean up some
> fallback code that is no longer supported.
> 
> The removed script was also testing for a GCC specific bug that was
> fixed in the 4.7 release.
> 
> Also remove workarounds for bpftrace using clang older than 9.0.0, since
> other BPF backend fixes are required at this point.
> 
> Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
> Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
> Acked-by: Borislav Petkov <bp@suse.de>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
> 
> Changes v1 -> v2:
> https://lore.kernel.org/linux-kbuild/20220819170053.2686006-1-ndesaulniers@google.com/
> * Pick up Boris' ack.
> * Drop line about Dash compat as per Alexandre.
> * Drop Alexandre's reported by as per Masahiro.
> * s/Kbuild/asm goto/ in oneline as per Masahiro.
> * Remove entirety of bpftrace workarounds as per Alexei.
> * Fix mistake in arch/x86/include/asm/rmwcc.h in v1 where I removed too
>   much; we still need guards for __GCC_ASM_FLAG_OUTPUTS__.
> 
>  Documentation/kbuild/kconfig-language.rst |  4 ++--
>  arch/Kconfig                              |  3 +--
>  arch/um/include/asm/cpufeature.h          | 15 ---------------
>  arch/x86/Makefile                         |  4 ----
>  arch/x86/include/asm/cpufeature.h         | 15 ---------------
>  arch/x86/include/asm/rmwcc.h              |  6 +++---
>  arch/x86/kvm/emulate.c                    |  2 +-
>  init/Kconfig                              |  4 ----
>  scripts/gcc-goto.sh                       | 22 ----------------------
>  tools/arch/x86/include/asm/rmwcc.h        | 21 ---------------------
>  10 files changed, 7 insertions(+), 89 deletions(-)
>  delete mode 100755 scripts/gcc-goto.sh
> 
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index 7fb398649f51..858ed5d80def 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -525,8 +525,8 @@ followed by a test macro::
>  If you need to expose a compiler capability to makefiles and/or C source files,
>  `CC_HAS_` is the recommended prefix for the config option::
>  
> -  config CC_HAS_ASM_GOTO
> -	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> +  config CC_HAS_FOO
> +	def_bool $(success,$(srctree)/scripts/cc-check-foo.sh $(CC))
>  
>  Build as module only
>  ~~~~~~~~~~~~~~~~~~~~
> diff --git a/arch/Kconfig b/arch/Kconfig
> index f330410da63a..5dbf11a5ba4e 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -53,7 +53,6 @@ config KPROBES
>  config JUMP_LABEL
>  	bool "Optimize very unlikely/likely branches"
>  	depends on HAVE_ARCH_JUMP_LABEL
> -	depends on CC_HAS_ASM_GOTO
>  	select OBJTOOL if HAVE_JUMP_LABEL_HACK
>  	help
>  	 This option enables a transparent branch optimization that
> @@ -1361,7 +1360,7 @@ config HAVE_PREEMPT_DYNAMIC_CALL
>  
>  config HAVE_PREEMPT_DYNAMIC_KEY
>  	bool
> -	depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
> +	depends on HAVE_ARCH_JUMP_LABEL
>  	select HAVE_PREEMPT_DYNAMIC
>  	help
>  	   An architecture should select this if it can handle the preemption
> diff --git a/arch/um/include/asm/cpufeature.h b/arch/um/include/asm/cpufeature.h
> index 19cd7ed6ec3c..4b6d1b526bc1 100644
> --- a/arch/um/include/asm/cpufeature.h
> +++ b/arch/um/include/asm/cpufeature.h
> @@ -65,20 +65,6 @@ extern void setup_clear_cpu_cap(unsigned int bit);
>  
>  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
>  
> -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> -
> -/*
> - * Workaround for the sake of BPF compilation which utilizes kernel
> - * headers, but clang does not support ASM GOTO and fails the build.
> - */
> -#ifndef __BPF_TRACING__
> -#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
> -#endif
> -
> -#define static_cpu_has(bit)            boot_cpu_has(bit)
> -
> -#else
> -
>  /*
>   * Static testing of CPU features. Used the same as boot_cpu_has(). It
>   * statically patches the target code for additional performance. Use
> @@ -137,7 +123,6 @@ static __always_inline bool _static_cpu_has(u16 bit)
>  		boot_cpu_has(bit) :				\
>  		_static_cpu_has(bit)				\
>  )
> -#endif
>  
>  #define cpu_has_bug(c, bit)		cpu_has(c, (bit))
>  #define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 7854685c5f25..bafbd905e6e7 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -286,10 +286,6 @@ vdso_install:
>  
>  archprepare: checkbin
>  checkbin:
> -ifndef CONFIG_CC_HAS_ASM_GOTO
> -	@echo Compiler lacks asm-goto support.
> -	@exit 1
> -endif
>  ifdef CONFIG_RETPOLINE
>  ifeq ($(RETPOLINE_CFLAGS),)
>  	@echo "You are building kernel with non-retpoline compiler." >&2
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index ea34cc31b047..1a85e1fb0922 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -155,20 +155,6 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
>  
>  #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
>  
> -#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
> -
> -/*
> - * Workaround for the sake of BPF compilation which utilizes kernel
> - * headers, but clang does not support ASM GOTO and fails the build.
> - */
> -#ifndef __BPF_TRACING__
> -#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
> -#endif
> -
> -#define static_cpu_has(bit)            boot_cpu_has(bit)
> -
> -#else
> -
>  /*
>   * Static testing of CPU features. Used the same as boot_cpu_has(). It
>   * statically patches the target code for additional performance. Use
> @@ -208,7 +194,6 @@ static __always_inline bool _static_cpu_has(u16 bit)
>  		boot_cpu_has(bit) :				\
>  		_static_cpu_has(bit)				\
>  )
> -#endif
>  
>  #define cpu_has_bug(c, bit)		cpu_has(c, (bit))
>  #define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))
> diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
> index 8a9eba191516..7fa611216417 100644
> --- a/arch/x86/include/asm/rmwcc.h
> +++ b/arch/x86/include/asm/rmwcc.h
> @@ -11,7 +11,7 @@
>  
>  #define __CLOBBERS_MEM(clb...)	"memory", ## clb
>  
> -#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CONFIG_CC_HAS_ASM_GOTO)
> +#ifndef __GCC_ASM_FLAG_OUTPUTS__
>  
>  /* Use asm goto */
>  
> @@ -27,7 +27,7 @@ cc_label:	c = true;						\
>  	c;								\
>  })
>  
> -#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> +#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
>  
>  /* Use flags output or a set instruction */
>  
> @@ -40,7 +40,7 @@ cc_label:	c = true;						\
>  	c;								\
>  })
>  
> -#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CONFIG_CC_HAS_ASM_GOTO) */
> +#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
>  
>  #define GEN_UNARY_RMWcc_4(op, var, cc, arg0)				\
>  	__GEN_RMWcc(op " " arg0, var, cc, __CLOBBERS_MEM())
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index b4eeb7c75dfa..08613c65138d 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -493,7 +493,7 @@ FOP_END;
>  
>  /*
>   * XXX: inoutclob user must know where the argument is being expanded.
> - *      Relying on CONFIG_CC_HAS_ASM_GOTO would allow us to remove _fault.
> + *      Using asm goto would allow us to remove _fault.
>   */
>  #define asm_safe(insn, inoutclob...) \
>  ({ \
> diff --git a/init/Kconfig b/init/Kconfig
> index 80fe60fa77fb..532362fcfe31 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -70,11 +70,7 @@ config CC_CAN_LINK_STATIC
>  	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
>  	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
>  
> -config CC_HAS_ASM_GOTO
> -	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> -
>  config CC_HAS_ASM_GOTO_OUTPUT
> -	depends on CC_HAS_ASM_GOTO
>  	def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
>  
>  config CC_HAS_ASM_GOTO_TIED_OUTPUT
> diff --git a/scripts/gcc-goto.sh b/scripts/gcc-goto.sh
> deleted file mode 100755
> index 8b980fb2270a..000000000000
> --- a/scripts/gcc-goto.sh
> +++ /dev/null
> @@ -1,22 +0,0 @@
> -#!/bin/sh
> -# SPDX-License-Identifier: GPL-2.0
> -# Test for gcc 'asm goto' support
> -# Copyright (C) 2010, Jason Baron <jbaron@redhat.com>
> -
> -cat << "END" | $@ -x c - -fno-PIE -c -o /dev/null
> -int main(void)
> -{
> -#if defined(__arm__) || defined(__aarch64__)
> -	/*
> -	 * Not related to asm goto, but used by jump label
> -	 * and broken on some ARM GCC versions (see GCC Bug 48637).
> -	 */
> -	static struct { int dummy; int state; } tp;
> -	asm (".long %c0" :: "i" (&tp.state));
> -#endif
> -
> -entry:
> -	asm goto ("" :::: entry);
> -	return 0;
> -}
> -END
> diff --git a/tools/arch/x86/include/asm/rmwcc.h b/tools/arch/x86/include/asm/rmwcc.h
> index fee7983a90b4..11ff975242ca 100644
> --- a/tools/arch/x86/include/asm/rmwcc.h
> +++ b/tools/arch/x86/include/asm/rmwcc.h
> @@ -2,8 +2,6 @@
>  #ifndef _TOOLS_LINUX_ASM_X86_RMWcc
>  #define _TOOLS_LINUX_ASM_X86_RMWcc
>  
> -#ifdef CONFIG_CC_HAS_ASM_GOTO
> -
>  #define __GEN_RMWcc(fullop, var, cc, ...)				\
>  do {									\
>  	asm_volatile_goto (fullop "; j" cc " %l[cc_label]"		\
> @@ -20,23 +18,4 @@ cc_label:								\
>  #define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
>  	__GEN_RMWcc(op " %1, " arg0, var, cc, vcon (val))
>  
> -#else /* !CONFIG_CC_HAS_ASM_GOTO */
> -
> -#define __GEN_RMWcc(fullop, var, cc, ...)				\
> -do {									\
> -	char c;								\
> -	asm volatile (fullop "; set" cc " %1"				\
> -			: "+m" (var), "=qm" (c)				\
> -			: __VA_ARGS__ : "memory");			\
> -	return c != 0;							\
> -} while (0)
> -
> -#define GEN_UNARY_RMWcc(op, var, arg0, cc)				\
> -	__GEN_RMWcc(op " " arg0, var, cc)
> -
> -#define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
> -	__GEN_RMWcc(op " %2, " arg0, var, cc, vcon (val))
> -
> -#endif /* CONFIG_CC_HAS_ASM_GOTO */
> -
>  #endif /* _TOOLS_LINUX_ASM_X86_RMWcc */
> -- 
> 2.37.1.595.g718a3a8f04-goog
> 
> 

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH v2] asm goto: eradicate CC_HAS_ASM_GOTO
  2022-08-19 19:06         ` [PATCH v2] asm goto: " Nick Desaulniers
  2022-08-19 20:04           ` Alexandre Belloni
  2022-08-19 21:48           ` Nathan Chancellor
@ 2022-08-21 10:11           ` Ingo Molnar
  2022-08-21 17:11           ` Linus Torvalds
  3 siblings, 0 replies; 13+ messages in thread
From: Ingo Molnar @ 2022-08-21 10:11 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Masahiro Yamada, Peter Zijlstra, x86, linux-kbuild, linux-doc,
	linux-kernel, linux-um, kvm, llvm, Linus Torvalds,
	Alexandre Belloni, Borislav Petkov, Alexei Starovoitov


* Nick Desaulniers <ndesaulniers@google.com> wrote:

> GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
> The minimum supported versions of these tools for the build according to
> Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.
> 
> Remove the feature detection script, Kconfig option, and clean up some
> fallback code that is no longer supported.
> 
> The removed script was also testing for a GCC specific bug that was
> fixed in the 4.7 release.
> 
> Also remove workarounds for bpftrace using clang older than 9.0.0, since
> other BPF backend fixes are required at this point.
> 
> Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
> Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
> Acked-by: Borislav Petkov <bp@suse.de>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Good riddance.

Thanks,

	Ingo

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH v2] asm goto: eradicate CC_HAS_ASM_GOTO
  2022-08-19 19:06         ` [PATCH v2] asm goto: " Nick Desaulniers
                             ` (2 preceding siblings ...)
  2022-08-21 10:11           ` Ingo Molnar
@ 2022-08-21 17:11           ` Linus Torvalds
  2022-08-22  6:11             ` Sedat Dilek
  3 siblings, 1 reply; 13+ messages in thread
From: Linus Torvalds @ 2022-08-21 17:11 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Masahiro Yamada, Peter Zijlstra, x86, linux-kbuild, linux-doc,
	linux-kernel, linux-um, kvm, llvm, Alexandre Belloni,
	Borislav Petkov, Alexei Starovoitov

Applied directly, just because I love seeing old nasty stuff like this go away.

             Linus

^ permalink raw reply	[flat|nested] 13+ messages in thread
* Re: [PATCH v2] asm goto: eradicate CC_HAS_ASM_GOTO
  2022-08-21 17:11           ` Linus Torvalds
@ 2022-08-22  6:11             ` Sedat Dilek
  0 siblings, 0 replies; 13+ messages in thread
From: Sedat Dilek @ 2022-08-22  6:11 UTC (permalink / raw)
  To: Linus Torvalds
  Cc: Nick Desaulniers, Masahiro Yamada, Peter Zijlstra, x86,
	linux-kbuild, linux-doc, linux-kernel, linux-um, kvm, llvm,
	Alexandre Belloni, Borislav Petkov, Alexei Starovoitov

On Sun, Aug 21, 2022 at 7:13 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Applied directly, just because I love seeing old nasty stuff like this go away.
>
>              Linus

Hi,

Small nitpick:

--- a/arch/x86/include/asm/rmwcc.h
+++ b/arch/x86/include/asm/rmwcc.h
...
-#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CONFIG_CC_HAS_ASM_GOTO)
+#ifndef __GCC_ASM_FLAG_OUTPUTS__
...
-#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) ||
!defined(CONFIG_CC_HAS_ASM_GOTO) */
+#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
...
-#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) ||
!defined(CONFIG_CC_HAS_ASM_GOTO) */
+#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) */

Shouldn't that be...

#if !defined(__GCC_ASM_FLAG_OUTPUTS__)

...to fit the 2 comments?

Best regards,
-Sedat-

^ permalink raw reply	[flat|nested] 13+ messages in thread
end of thread, other threads:[~2022-08-22  6:12 UTC | newest]

Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-08-19 17:00 [PATCH] Kconfig: eradicate CC_HAS_ASM_GOTO Nick Desaulniers
2022-08-19 17:11 ` Borislav Petkov
2022-08-19 17:16 ` Alexandre Belloni
2022-08-19 17:28   ` Nick Desaulniers
2022-08-19 17:41     ` Masahiro Yamada
2022-08-19 18:31       ` Alexei Starovoitov
2022-08-19 19:06         ` [PATCH v2] asm goto: " Nick Desaulniers
2022-08-19 20:04           ` Alexandre Belloni
2022-08-19 21:48           ` Nathan Chancellor
2022-08-21 10:11           ` Ingo Molnar
2022-08-21 17:11           ` Linus Torvalds
2022-08-22  6:11             ` Sedat Dilek
2022-08-19 18:45 ` [PATCH] Kconfig: " Nick Desaulniers

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