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Code Issues Releases Wiki Activity

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>
This commit is contained in:
Nick Desaulniers 2022-08-19 12:06:40 -07:00 committed by Linus Torvalds
parent 15b3f48a43
commit a0a12c3ed0
10 changed files with 7 additions and 89 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
Documentation/kbuild/kconfig-language.rst
View File

@ -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
~~~~~~~~~~~~~~~~~~~~

3
arch/Kconfig
View File

@ -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

15
arch/um/include/asm/cpufeature.h
View File

@ -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))

4
arch/x86/Makefile
View File

@ -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

15
arch/x86/include/asm/cpufeature.h
View File

@ -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))

6
arch/x86/include/asm/rmwcc.h
View File

@ -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())

2
arch/x86/kvm/emulate.c
View File

@ -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...) \
({ \

4
init/Kconfig
View File

@ -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

22
scripts/gcc-goto.sh
View File

@ -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

21
tools/arch/x86/include/asm/rmwcc.h
View File

@ -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 */