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Merge tag 'core-headers-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull header cleanup from Ingo Molnar:
 "Separate out the instrumentation_begin()/end() bits from compiler.h"

* tag 'core-headers-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  compiler.h: Move instrumentation_begin()/end() to new <linux/instrumentation.h> header
This commit is contained in:
Linus Torvalds
2020-08-03 14:25:40 -07:00
parent c8e69391d0 d19e789f06
commit 5ece08178d
5 changed files with 61 additions and 53 deletions
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1
arch/x86/include/asm/bug.h
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@@ -3,6 +3,7 @@
#define _ASM_X86_BUG_H #define _ASM_X86_BUG_H
#include <linux/stringify.h> #include <linux/stringify.h>
#include <linux/instrumentation.h>
/* /*
* Despite that some emulators terminate on UD2, we use it for WARN(). * Despite that some emulators terminate on UD2, we use it for WARN().

1
include/asm-generic/bug.h
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@@ -3,6 +3,7 @@
#define _ASM_GENERIC_BUG_H #define _ASM_GENERIC_BUG_H
#include <linux/compiler.h> #include <linux/compiler.h>
#include <linux/instrumentation.h>
#define CUT_HERE "------------[ cut here ]------------\n" #define CUT_HERE "------------[ cut here ]------------\n"

53
include/linux/compiler.h
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@@ -120,65 +120,12 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
/* Annotate a C jump table to allow objtool to follow the code flow */ /* Annotate a C jump table to allow objtool to follow the code flow */
#define __annotate_jump_table __section(.rodata..c_jump_table) #define __annotate_jump_table __section(.rodata..c_jump_table)
#ifdef CONFIG_DEBUG_ENTRY
/* Begin/end of an instrumentation safe region */
#define instrumentation_begin() ({ \
asm volatile("%c0: nop\n\t" \
".pushsection .discard.instr_begin\n\t" \
".long %c0b - .\n\t" \
".popsection\n\t" : : "i" (__COUNTER__)); \
})
/*
* Because instrumentation_{begin,end}() can nest, objtool validation considers
* _begin() a +1 and _end() a -1 and computes a sum over the instructions.
* When the value is greater than 0, we consider instrumentation allowed.
*
* There is a problem with code like:
*
* noinstr void foo()
* {
* instrumentation_begin();
* ...
* if (cond) {
* instrumentation_begin();
* ...
* instrumentation_end();
* }
* bar();
* instrumentation_end();
* }
*
* If instrumentation_end() would be an empty label, like all the other
* annotations, the inner _end(), which is at the end of a conditional block,
* would land on the instruction after the block.
*
* If we then consider the sum of the !cond path, we'll see that the call to
* bar() is with a 0-value, even though, we meant it to happen with a positive
* value.
*
* To avoid this, have _end() be a NOP instruction, this ensures it will be
* part of the condition block and does not escape.
*/
#define instrumentation_end() ({ \
asm volatile("%c0: nop\n\t" \
".pushsection .discard.instr_end\n\t" \
".long %c0b - .\n\t" \
".popsection\n\t" : : "i" (__COUNTER__)); \
})
#endif /* CONFIG_DEBUG_ENTRY */
#else #else
#define annotate_reachable() #define annotate_reachable()
#define annotate_unreachable() #define annotate_unreachable()
#define __annotate_jump_table #define __annotate_jump_table
#endif #endif
#ifndef instrumentation_begin
#define instrumentation_begin() do { } while(0)
#define instrumentation_end() do { } while(0)
#endif
#ifndef ASM_UNREACHABLE #ifndef ASM_UNREACHABLE
# define ASM_UNREACHABLE # define ASM_UNREACHABLE
#endif #endif

2
include/linux/context_tracking.h
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@@ -5,6 +5,8 @@
#include <linux/sched.h> #include <linux/sched.h>
#include <linux/vtime.h> #include <linux/vtime.h>
#include <linux/context_tracking_state.h> #include <linux/context_tracking_state.h>
#include <linux/instrumentation.h>
#include <asm/ptrace.h> #include <asm/ptrace.h>

57
include/linux/instrumentation.h Normal file
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@@ -0,0 +1,57 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_INSTRUMENTATION_H
#define __LINUX_INSTRUMENTATION_H
#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION)
/* Begin/end of an instrumentation safe region */
#define instrumentation_begin() ({ \
asm volatile("%c0: nop\n\t" \
".pushsection .discard.instr_begin\n\t" \
".long %c0b - .\n\t" \
".popsection\n\t" : : "i" (__COUNTER__)); \
})
/*
* Because instrumentation_{begin,end}() can nest, objtool validation considers
* _begin() a +1 and _end() a -1 and computes a sum over the instructions.
* When the value is greater than 0, we consider instrumentation allowed.
*
* There is a problem with code like:
*
* noinstr void foo()
* {
* instrumentation_begin();
* ...
* if (cond) {
* instrumentation_begin();
* ...
* instrumentation_end();
* }
* bar();
* instrumentation_end();
* }
*
* If instrumentation_end() would be an empty label, like all the other
* annotations, the inner _end(), which is at the end of a conditional block,
* would land on the instruction after the block.
*
* If we then consider the sum of the !cond path, we'll see that the call to
* bar() is with a 0-value, even though, we meant it to happen with a positive
* value.
*
* To avoid this, have _end() be a NOP instruction, this ensures it will be
* part of the condition block and does not escape.
*/
#define instrumentation_end() ({ \
asm volatile("%c0: nop\n\t" \
".pushsection .discard.instr_end\n\t" \
".long %c0b - .\n\t" \
".popsection\n\t" : : "i" (__COUNTER__)); \
})
#else
# define instrumentation_begin() do { } while(0)
# define instrumentation_end() do { } while(0)
#endif
#endif /* __LINUX_INSTRUMENTATION_H */