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 <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>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
index 7fb3986..858ed5d 100644 (file)
--- 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 f330410..5dbf11a 100644 (file)
--- 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 19cd7ed..4b6d1b5 100644 (file)
--- 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 @@ t_no:
                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 7854685..bafbd90 100644 (file)
--- 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 ea34cc3..1a85e1f 100644 (file)
--- 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 @@ t_no:
                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 8a9eba1..7fa6112 100644 (file)
--- 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 f092c54..d5ec3a2 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/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...) \
 ({ \

diff --git a/init/Kconfig b/init/Kconfig
index 80fe60f..532362f 100644 (file)
--- 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 (executable)
index 8b980fb..0000000
--- 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 fee7983..11ff975 100644 (file)
--- 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 */