On 2/24/22 05:28, Vishal Verma wrote:
> Add a fallback for older compilers that lack __builtin_add_overflow()
> and friends. Commit 7aa7c7be6e80 ("util: add the struct_size() helper from the
> kernel") which added these helpers from the kernel neglected to copy
> over the fallback code.
>
> Fixes: 7aa7c7be6e80 ("util: add the struct_size() helper from the kernel")
> Reported-by: Joao Martins <[email protected]>
> Signed-off-by: Vishal Verma <[email protected]>
Reviewed-by: Joao Martins <[email protected]>
You might wanna want this to get to v72.y branch considering the breakage exists
there. Thanks for the followup!
> ---
> util/size.h | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 159 insertions(+), 4 deletions(-)
>
> diff --git a/util/size.h b/util/size.h
> index e72467f..1cb0669 100644
> --- a/util/size.h
> +++ b/util/size.h
> @@ -6,6 +6,7 @@
> #include <stdbool.h>
> #include <stdint.h>
> #include <util/util.h>
> +#include <ccan/short_types/short_types.h>
>
> #define SZ_1K 0x00000400
> #define SZ_4K 0x00001000
> @@ -43,23 +44,177 @@ static inline bool is_power_of_2(unsigned long long v)
> * alias for __builtin_add_overflow, but add type checks similar to
> * below.
> */
> -#define check_add_overflow(a, b, d) (({ \
> +#define is_signed_type(type) (((type)(-1)) < (type)1)
> +#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 -
> is_signed_type(type)))
> +#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
> +#define type_min(T) ((T)((T)-type_max(T)-(T)1))
> +
> +#if GCC_VERSION >= 50100
> +#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
> +#endif
> +
> +#if __clang__ && \
> + __has_builtin(__builtin_mul_overflow) && \
> + __has_builtin(__builtin_add_overflow)
> +#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
> +#endif
> +
> +#if COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
> +
> +#define check_add_overflow(a, b, d) ({ \
> typeof(a) __a = (a); \
> typeof(b) __b = (b); \
> typeof(d) __d = (d); \
> (void) (&__a == &__b); \
> (void) (&__a == __d); \
> __builtin_add_overflow(__a, __b, __d); \
> -}))
> +})
>
> -#define check_mul_overflow(a, b, d) (({ \
> +#define check_sub_overflow(a, b, d) ({ \
> + typeof(a) __a = (a); \
> + typeof(b) __b = (b); \
> + typeof(d) __d = (d); \
> + (void) (&__a == &__b); \
> + (void) (&__a == __d); \
> + __builtin_sub_overflow(__a, __b, __d); \
> +})
> +
> +#define check_mul_overflow(a, b, d) ({ \
> typeof(a) __a = (a); \
> typeof(b) __b = (b); \
> typeof(d) __d = (d); \
> (void) (&__a == &__b); \
> (void) (&__a == __d); \
> __builtin_mul_overflow(__a, __b, __d); \
> -}))
> +})
> +
> +
> +#else /* !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
> +
> +/* Checking for unsigned overflow is relatively easy without causing UB. */
> +#define __unsigned_add_overflow(a, b, d) ({ \
> + typeof(a) __a = (a); \
> + typeof(b) __b = (b); \
> + typeof(d) __d = (d); \
> + (void) (&__a == &__b); \
> + (void) (&__a == __d); \
> + *__d = __a + __b; \
> + *__d < __a; \
> +})
> +#define __unsigned_sub_overflow(a, b, d) ({ \
> + typeof(a) __a = (a); \
> + typeof(b) __b = (b); \
> + typeof(d) __d = (d); \
> + (void) (&__a == &__b); \
> + (void) (&__a == __d); \
> + *__d = __a - __b; \
> + __a < __b; \
> +})
> +/*
> + * If one of a or b is a compile-time constant, this avoids a division.
> + */
> +#define __unsigned_mul_overflow(a, b, d) ({ \
> + typeof(a) __a = (a); \
> + typeof(b) __b = (b); \
> + typeof(d) __d = (d); \
> + (void) (&__a == &__b); \
> + (void) (&__a == __d); \
> + *__d = __a * __b; \
> + __builtin_constant_p(__b) ? \
> + __b > 0 && __a > type_max(typeof(__a)) / __b : \
> + __a > 0 && __b > type_max(typeof(__b)) / __a; \
> +})
> +
> +/*
> + * For signed types, detecting overflow is much harder, especially if
> + * we want to avoid UB. But the interface of these macros is such that
> + * we must provide a result in *d, and in fact we must produce the
> + * result promised by gcc's builtins, which is simply the possibly
> + * wrapped-around value. Fortunately, we can just formally do the
> + * operations in the widest relevant unsigned type (u64) and then
> + * truncate the result - gcc is smart enough to generate the same code
> + * with and without the (u64) casts.
> + */
> +
> +/*
> + * Adding two signed integers can overflow only if they have the same
> + * sign, and overflow has happened iff the result has the opposite
> + * sign.
> + */
> +#define __signed_add_overflow(a, b, d) ({ \
> + typeof(a) __a = (a); \
> + typeof(b) __b = (b); \
> + typeof(d) __d = (d); \
> + (void) (&__a == &__b); \
> + (void) (&__a == __d); \
> + *__d = (u64)__a + (u64)__b; \
> + (((~(__a ^ __b)) & (*__d ^ __a)) \
> + & type_min(typeof(__a))) != 0; \
> +})
> +
> +/*
> + * Subtraction is similar, except that overflow can now happen only
> + * when the signs are opposite. In this case, overflow has happened if
> + * the result has the opposite sign of a.
> + */
> +#define __signed_sub_overflow(a, b, d) ({ \
> + typeof(a) __a = (a); \
> + typeof(b) __b = (b); \
> + typeof(d) __d = (d); \
> + (void) (&__a == &__b); \
> + (void) (&__a == __d); \
> + *__d = (u64)__a - (u64)__b; \
> + ((((__a ^ __b)) & (*__d ^ __a)) \
> + & type_min(typeof(__a))) != 0; \
> +})
> +
> +/*
> + * Signed multiplication is rather hard. gcc always follows C99, so
> + * division is truncated towards 0. This means that we can write the
> + * overflow check like this:
> + *
> + * (a > 0 && (b > MAX/a || b < MIN/a)) ||
> + * (a < -1 && (b > MIN/a || b < MAX/a) ||
> + * (a == -1 && b == MIN)
> + *
> + * The redundant casts of -1 are to silence an annoying -Wtype-limits
> + * (included in -Wextra) warning: When the type is u8 or u16, the
> + * __b_c_e in check_mul_overflow obviously selects
> + * __unsigned_mul_overflow, but unfortunately gcc still parses this
> + * code and warns about the limited range of __b.
> + */
> +
> +#define __signed_mul_overflow(a, b, d) ({ \
> + typeof(a) __a = (a); \
> + typeof(b) __b = (b); \
> + typeof(d) __d = (d); \
> + typeof(a) __tmax = type_max(typeof(a)); \
> + typeof(a) __tmin = type_min(typeof(a)); \
> + (void) (&__a == &__b); \
> + (void) (&__a == __d); \
> + *__d = (u64)__a * (u64)__b; \
> + (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
> + (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
> + (__b == (typeof(__b))-1 && __a == __tmin); \
> +})
> +
> +
> +#define check_add_overflow(a, b, d) \
> + __builtin_choose_expr(is_signed_type(typeof(a)), \
> + __signed_add_overflow(a, b, d), \
> + __unsigned_add_overflow(a, b, d))
> +
> +#define check_sub_overflow(a, b, d) \
> + __builtin_choose_expr(is_signed_type(typeof(a)), \
> + __signed_sub_overflow(a, b, d), \
> + __unsigned_sub_overflow(a, b, d))
> +
> +#define check_mul_overflow(a, b, d) \
> + __builtin_choose_expr(is_signed_type(typeof(a)), \
> + __signed_mul_overflow(a, b, d), \
> + __unsigned_mul_overflow(a, b, d))
> +
> +#endif
>
> /*
> * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
>
> base-commit: 3e4a66f0dfb02046f6d3375d637840b6da9c71d1
