diff options
Diffstat (limited to 'include/linux/compiler.h')
| -rw-r--r-- | include/linux/compiler.h | 175 |
1 files changed, 134 insertions, 41 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index bb1339c7057b..155385754824 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -109,35 +109,21 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, /* Unreachable code */ #ifdef CONFIG_OBJTOOL -/* - * These macros help objtool understand GCC code flow for unreachable code. - * The __COUNTER__ based labels are a hack to make each instance of the macros - * unique, to convince GCC not to merge duplicate inline asm statements. - */ -#define __stringify_label(n) #n - -#define __annotate_unreachable(c) ({ \ - asm volatile(__stringify_label(c) ":\n\t" \ - ".pushsection .discard.unreachable\n\t" \ - ".long " __stringify_label(c) "b - .\n\t" \ - ".popsection\n\t" : : "i" (c)); \ -}) -#define annotate_unreachable() __annotate_unreachable(__COUNTER__) - /* 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(".data.rel.ro.c_jump_table") #else /* !CONFIG_OBJTOOL */ -#define annotate_unreachable() #define __annotate_jump_table #endif /* CONFIG_OBJTOOL */ -#ifndef unreachable -# define unreachable() do { \ - annotate_unreachable(); \ +/* + * Mark a position in code as unreachable. This can be used to + * suppress control flow warnings after asm blocks that transfer + * control elsewhere. + */ +#define unreachable() do { \ + barrier_before_unreachable(); \ __builtin_unreachable(); \ } while (0) -#endif /* * KENTRY - kernel entry point @@ -185,33 +171,46 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, * This data_race() macro is useful for situations in which data races * should be forgiven. One example is diagnostic code that accesses * shared variables but is not a part of the core synchronization design. + * For example, if accesses to a given variable are protected by a lock, + * except for diagnostic code, then the accesses under the lock should + * be plain C-language accesses and those in the diagnostic code should + * use data_race(). This way, KCSAN will complain if buggy lockless + * accesses to that variable are introduced, even if the buggy accesses + * are protected by READ_ONCE() or WRITE_ONCE(). * * This macro *does not* affect normal code generation, but is a hint - * to tooling that data races here are to be ignored. + * to tooling that data races here are to be ignored. If the access must + * be atomic *and* KCSAN should ignore the access, use both data_race() + * and READ_ONCE(), for example, data_race(READ_ONCE(x)). */ #define data_race(expr) \ ({ \ - __unqual_scalar_typeof(({ expr; })) __v = ({ \ - __kcsan_disable_current(); \ - expr; \ - }); \ + __kcsan_disable_current(); \ + __auto_type __v = (expr); \ __kcsan_enable_current(); \ __v; \ }) -#endif /* __KERNEL__ */ +#ifdef __CHECKER__ +#define __BUILD_BUG_ON_ZERO_MSG(e, msg) (0) +#else /* __CHECKER__ */ +#define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);})) +#endif /* __CHECKER__ */ -/* - * Force the compiler to emit 'sym' as a symbol, so that we can reference - * it from inline assembler. Necessary in case 'sym' could be inlined - * otherwise, or eliminated entirely due to lack of references that are - * visible to the compiler. - */ -#define ___ADDRESSABLE(sym, __attrs) \ - static void * __used __attrs \ - __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)&sym; -#define __ADDRESSABLE(sym) \ - ___ADDRESSABLE(sym, __section(".discard.addressable")) +/* &a[0] degrades to a pointer: a different type from an array */ +#define __is_array(a) (!__same_type((a), &(a)[0])) +#define __must_be_array(a) __BUILD_BUG_ON_ZERO_MSG(!__is_array(a), \ + "must be array") + +#define __is_byte_array(a) (__is_array(a) && sizeof((a)[0]) == 1) +#define __must_be_byte_array(a) __BUILD_BUG_ON_ZERO_MSG(!__is_byte_array(a), \ + "must be byte array") + +/* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */ +#define __must_be_cstr(p) \ + __BUILD_BUG_ON_ZERO_MSG(__annotated(p, nonstring), "must be cstr (NUL-terminated)") + +#endif /* __KERNEL__ */ /** * offset_to_ptr - convert a relative memory offset to an absolute pointer @@ -224,13 +223,76 @@ static inline void *offset_to_ptr(const int *off) #endif /* __ASSEMBLY__ */ -/* &a[0] degrades to a pointer: a different type from an array */ -#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0])) +#ifdef CONFIG_64BIT +#define ARCH_SEL(a,b) a +#else +#define ARCH_SEL(a,b) b +#endif + +/* + * Force the compiler to emit 'sym' as a symbol, so that we can reference + * it from inline assembler. Necessary in case 'sym' could be inlined + * otherwise, or eliminated entirely due to lack of references that are + * visible to the compiler. + */ +#define ___ADDRESSABLE(sym, __attrs) \ + static void * __used __attrs \ + __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)(uintptr_t)&sym; + +#define __ADDRESSABLE(sym) \ + ___ADDRESSABLE(sym, __section(".discard.addressable")) + +#define __ADDRESSABLE_ASM(sym) \ + .pushsection .discard.addressable,"aw"; \ + .align ARCH_SEL(8,4); \ + ARCH_SEL(.quad, .long) __stringify(sym); \ + .popsection; + +#define __ADDRESSABLE_ASM_STR(sym) __stringify(__ADDRESSABLE_ASM(sym)) /* * This returns a constant expression while determining if an argument is * a constant expression, most importantly without evaluating the argument. * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de> + * + * Details: + * - sizeof() return an integer constant expression, and does not evaluate + * the value of its operand; it only examines the type of its operand. + * - The results of comparing two integer constant expressions is also + * an integer constant expression. + * - The first literal "8" isn't important. It could be any literal value. + * - The second literal "8" is to avoid warnings about unaligned pointers; + * this could otherwise just be "1". + * - (long)(x) is used to avoid warnings about 64-bit types on 32-bit + * architectures. + * - The C Standard defines "null pointer constant", "(void *)0", as + * distinct from other void pointers. + * - If (x) is an integer constant expression, then the "* 0l" resolves + * it into an integer constant expression of value 0. Since it is cast to + * "void *", this makes the second operand a null pointer constant. + * - If (x) is not an integer constant expression, then the second operand + * resolves to a void pointer (but not a null pointer constant: the value + * is not an integer constant 0). + * - The conditional operator's third operand, "(int *)8", is an object + * pointer (to type "int"). + * - The behavior (including the return type) of the conditional operator + * ("operand1 ? operand2 : operand3") depends on the kind of expressions + * given for the second and third operands. This is the central mechanism + * of the macro: + * - When one operand is a null pointer constant (i.e. when x is an integer + * constant expression) and the other is an object pointer (i.e. our + * third operand), the conditional operator returns the type of the + * object pointer operand (i.e. "int *"). Here, within the sizeof(), we + * would then get: + * sizeof(*((int *)(...)) == sizeof(int) == 4 + * - When one operand is a void pointer (i.e. when x is not an integer + * constant expression) and the other is an object pointer (i.e. our + * third operand), the conditional operator returns a "void *" type. + * Here, within the sizeof(), we would then get: + * sizeof(*((void *)(...)) == sizeof(void) == 1 + * - The equality comparison to "sizeof(int)" therefore depends on (x): + * sizeof(int) == sizeof(int) (x) was a constant expression + * sizeof(int) != sizeof(void) (x) was not a constant expression */ #define __is_constexpr(x) \ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) @@ -243,6 +305,37 @@ static inline void *offset_to_ptr(const int *off) #define is_unsigned_type(type) (!is_signed_type(type)) /* + * Useful shorthand for "is this condition known at compile-time?" + * + * Note that the condition may involve non-constant values, + * but the compiler may know enough about the details of the + * values to determine that the condition is statically true. + */ +#define statically_true(x) (__builtin_constant_p(x) && (x)) + +/* + * Similar to statically_true() but produces a constant expression + * + * To be used in conjunction with macros, such as BUILD_BUG_ON_ZERO(), + * which require their input to be a constant expression and for which + * statically_true() would otherwise fail. + * + * This is a trade-off: const_true() requires all its operands to be + * compile time constants. Else, it would always returns false even on + * the most trivial cases like: + * + * true || non_const_var + * + * On the opposite, statically_true() is able to fold more complex + * tautologies and will return true on expressions such as: + * + * !(non_const_var * 8 % 4) + * + * For the general case, statically_true() is better. + */ +#define const_true(x) __builtin_choose_expr(__is_constexpr(x), x, false) + +/* * This is needed in functions which generate the stack canary, see * arch/x86/kernel/smpboot.c::start_secondary() for an example. */ |