Re: [PATCH 2/2] qemu_process: Fix theoretical overflow in uint to bool typecast

On Wed, Feb 09, 2022 at 09:39:50 +0100, Michal Privoznik wrote: I don't think that this is accurate as casting a unsigned int (32bits) to a bool (8 bits) works properly even when the lower 8 bits of the value equal to 0: $ cat bool.c #include <stdint.h> #include <stdio.h> #include <limits.h> #include <stdbool.h> void p(char *s, unsigned long long v, uint8_t u, bool b) { printf("%30s: %30llu: %4u: %d\n", s, v, u, b); } #define E(val) \ p(#val, (val), (val), (val)) #define T(type) \ E(type - 1);\ E(type);\ E(type + 1) int main() { printf("bool size: %u\n", sizeof(bool)); E(0); T(CHAR_MAX); T(UCHAR_MAX); T(UINT8_MAX); T(INT_MAX); T(UINT_MAX); } $ ./a.out bool size: 1 0: 0: 0: 0 0x7f - 1: 126: 126: 1 0x7f: 127: 127: 1 0x7f + 1: 128: 128: 1 (0x7f * 2 + 1) - 1: 254: 254: 1 (0x7f * 2 + 1): 255: 255: 1 (0x7f * 2 + 1) + 1: 256: 0: 1 (255) - 1: 254: 254: 1 (255): 255: 255: 1 (255) + 1: 256: 0: 1 0x7fffffff - 1: 2147483646: 254: 1 0x7fffffff: 2147483647: 255: 1 0x7fffffff + 1: 18446744071562067968: 0: 1 (0x7fffffff * 2U + 1U) - 1: 4294967294: 254: 1 (0x7fffffff * 2U + 1U): 4294967295: 255: 1 (0x7fffffff * 2U + 1U) + 1: 0: 0: 0 I have no problem with the code change to make it use our common pattern.