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243c90e917
__BUILD_BUG_ON_ZERO_MSG(), as introduced in [1], makes it possible to
do a static assertions in expressions. The direct benefit is to
provide a meaningful error message instead of the cryptic negative
bitfield size error message currently returned by BUILD_BUG_ON_ZERO():
./include/linux/build_bug.h:16:51: error: negative width in bit-field '<anonymous>'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
Get rid of BUILD_BUG_ON_ZERO()'s bitfield size hack. Instead rely on
__BUILD_BUG_ON_ZERO_MSG() which in turn relies on C11's
_Static_assert().
Use some macro magic, similarly to static_assert(), to either use an
optional error message provided by the user or, when omitted, to
produce a default error message by stringifying the tested
expression. With this, for example:
BUILD_BUG_ON_ZERO(1 > 0)
would now throw:
./include/linux/compiler.h:197:62: error: static assertion failed: "1 > 0 is true"
197 | define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
| ^~~~~~~~~~~~~~
Finally, __BUILD_BUG_ON_ZERO_MSG() is already guarded by an:
#ifdef __CHECKER__
So no need any more for that guard clause for BUILD_BUG_ON_ZERO().
Remove it.
[1] commit d7a516c6ee ("compiler.h: Fix undefined BUILD_BUG_ON_ZERO()")
Link: https://git.kernel.org/torvalds/c/d7a516c6eeae
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://git.kernel.org/next/linux-next/c/b88937277df
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
90 lines
3.0 KiB
C
90 lines
3.0 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_BUILD_BUG_H
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#define _LINUX_BUILD_BUG_H
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#include <linux/compiler.h>
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/*
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* Force a compilation error if condition is true, but also produce a
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* result (of value 0 and type int), so the expression can be used
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* e.g. in a structure initializer (or where-ever else comma expressions
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* aren't permitted).
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*
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* Take an error message as an optional second argument. If omitted,
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* default to the stringification of the tested expression.
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*/
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#define BUILD_BUG_ON_ZERO(e, ...) \
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__BUILD_BUG_ON_ZERO_MSG(e, ##__VA_ARGS__, #e " is true")
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/* Force a compilation error if a constant expression is not a power of 2 */
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#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) \
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BUILD_BUG_ON(((n) & ((n) - 1)) != 0)
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#define BUILD_BUG_ON_NOT_POWER_OF_2(n) \
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BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
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/*
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* BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
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* expression but avoids the generation of any code, even if that expression
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* has side-effects.
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*/
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#define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
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/**
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* BUILD_BUG_ON_MSG - break compile if a condition is true & emit supplied
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* error message.
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* @condition: the condition which the compiler should know is false.
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*
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* See BUILD_BUG_ON for description.
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*/
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#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
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/**
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* BUILD_BUG_ON - break compile if a condition is true.
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* @condition: the condition which the compiler should know is false.
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*
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* If you have some code which relies on certain constants being equal, or
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* some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
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* detect if someone changes it.
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*/
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#define BUILD_BUG_ON(condition) \
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BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
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/**
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* BUILD_BUG - break compile if used.
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*
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* If you have some code that you expect the compiler to eliminate at
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* build time, you should use BUILD_BUG to detect if it is
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* unexpectedly used.
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*/
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#define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
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/**
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* static_assert - check integer constant expression at build time
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*
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* static_assert() is a wrapper for the C11 _Static_assert, with a
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* little macro magic to make the message optional (defaulting to the
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* stringification of the tested expression).
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*
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* Contrary to BUILD_BUG_ON(), static_assert() can be used at global
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* scope, but requires the expression to be an integer constant
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* expression (i.e., it is not enough that __builtin_constant_p() is
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* true for expr).
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*
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* Also note that BUILD_BUG_ON() fails the build if the condition is
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* true, while static_assert() fails the build if the expression is
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* false.
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*/
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#define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
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#define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
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/*
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* Compile time check that field has an expected offset
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*/
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#define ASSERT_STRUCT_OFFSET(type, field, expected_offset) \
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BUILD_BUG_ON_MSG(offsetof(type, field) != (expected_offset), \
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"Offset of " #field " in " #type " has changed.")
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#endif /* _LINUX_BUILD_BUG_H */
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