asm goto: eradicate CC_HAS_ASM_GOTO

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 <[email protected]>
Suggested-by: Masahiro Yamada <[email protected]>
Suggested-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Reviewed-by: Ingo Molnar <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Reviewed-by: Alexandre Belloni <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: nickdesaulniers

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
 ~~~~~~~~~~~~~~~~~~~~

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

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))

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

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))

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())

arch/x86/kvm/emulate.c

@@ -479,7 +479,7 @@ 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...) \
 ({ \

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

scripts/gcc-goto.sh

@@ -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 */