On Fri, Aug 16, 2024 at 04:32:48PM +0100, Andre Przywara wrote:
> When masking the return value of a prctl, which is clearly an "int", we
> use a uapi header provided mask, which is defined using an "UL" modifier,
> so the whole expression is promoted to a long. This upsets the compiler's
> printf type checker, because we use "%x" in the format string.
>
> While we could simply upgrade this to a "%lx", it sounds wrong to
> promote the "ret" variable, that is clearly an int.
> Downcast the mask instead, to keep the type correct.
This suggests that we've got some confusion with the UAPI, these flags
need to go through a prctl() return so they shouldn't be unsigned
long... That said, it's UAPI so I'm not sure that's fixable.
> - if ((ret & PR_MTE_TCF_MASK) == mask) {
> + if ((ret & (int)PR_MTE_TCF_MASK) == mask) {
> ksft_test_result_pass("%s\n", name);
> } else {
> ksft_print_msg("Got %x, expected %x\n",
> - (ret & PR_MTE_TCF_MASK), mask);
> + (ret & (int)PR_MTE_TCF_MASK), mask);
> ksft_test_result_fail("%s\n", name);
TBH my inclination is that this is worse than letting the value be
promoted, casts (particularly casts of constants) are just obviously
suspect in a way that printf() formats aren't.
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