On Wed, Feb 09, 2022 at 09:39:50 +0100, Michal Privoznik wrote:
> The qemuPrepareNVRAM() function accepts three arguments and the
> last one being a boolean type. However, when the function is
> called from qemuProcessPrepareHost() the argument passed is a
> result of logical and of @flags (unsigned int) and
> VIR_QEMU_PROCESS_START_RESET_NVRAM value. In theory this is
> unsafe to do because if the value of the flag is ever changed
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
> then this expression might overflow. Do what we do elsewhere:
> double negation.
I have no problem with the code change to make it use our common
pattern.
> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> ---
> src/qemu/qemu_process.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index 7066696f31..24873f6fb7 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -6983,7 +6983,7 @@ qemuProcessPrepareHost(virQEMUDriver *driver,
> qemuProcessMakeDir(driver, vm, priv->channelTargetDir) < 0)
> return -1;
>
> - if (qemuPrepareNVRAM(driver, vm, flags & VIR_QEMU_PROCESS_START_RESET_NVRAM) < 0)
> + if (qemuPrepareNVRAM(driver, vm, !!(flags & VIR_QEMU_PROCESS_START_RESET_NVRAM)) < 0)
> return -1;
>
> if (vm->def->vsock) {
> --
> 2.34.1
>
