2015-06-22 13:18 GMT+03:00 David Faure <fa...@kde.org>:
> I don't follow. How does 0x858458F6 not fit into an int, even on a 32 bit
> machine?
> OK, this is just about signed/unsigned, not about really wider.
> So yeah the bug is that glibc should use unsigned int there instead,
> but the issue you mention "the comparison will fail" might not happen, if the
> comparison uses the right signedness. There is no truncation happening, at
> least.
>
> A static_cast<unsigned int> workaround in kcoreaddons would work in practice,
> no?
David,
I believe in the same theory you described.
I couldn't reproduce the error on clang x86_64, even though I tried
hard. The most I could get is a warning "overflow converting case
value to switch condition type (2240043254 to -2054924042)" when you
change 0x858458F6 to 0x858458F6LL to make it be not convertible to a
4-byte signed int (see attached .cpp file.)
The hack with static_cast<unsigned int>() helps here, but we need to
use something more portable than "unsigned int", because on x86_64
sizeof(statfs.f_type) == 8, i.e. differs from unsigned int.
--
Alexander Potashev
#include <iostream>
#include <sys/statfs.h>
#define RAMFS_MAGIC 0x858458F6LL
int main()
{
int x = 0x858458F6;
std::cout << x << std::endl;
switch (x)
//switch (static_cast<unsigned int>(x))
{
case RAMFS_MAGIC:
std::cout << "hi!" << std::endl;
break;
default:
break;
}
struct statfs s;
std::cout << sizeof(s.f_type) << std::endl; // Prints 8 on x86_64
return 0;
}
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