Re: [RFC PATCH 2/2] linux-user/mmap: Fix Clang 'type-limit-compare' warning

[Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>]

нед, 3. мај 2020. у 13:33 Philippe Mathieu-Daudé <f4bug@amsat.org> је
написао/ла:
>
> When building with Clang 10 on Fedora 32, we get:
>
>     CC      linux-user/mmap.o
>   linux-user/mmap.c:720:49: error: result of comparison 'unsigned long' > 18446744073709551615 is always false [-Werror,-Wtautological-type-limit-compare]
>           if ((unsigned long)host_addr + new_size > (abi_ulong)-1) {
>               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
>
> Fix by restricting the check for when target sizeof(abi_ulong) is
> smaller than target sizeof(unsigned long).
>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  linux-user/mmap.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index e378033797..b14652d894 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -714,6 +714,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
>              errno = ENOMEM;
>              host_addr = MAP_FAILED;
>          }
> +#if TARGET_ABI_BITS < TARGET_LONG_BITS
>          /* Check if address fits target address space */
>          if ((unsigned long)host_addr + new_size > (abi_ulong)-1) {
>              /* Revert mremap() changes */
> @@ -721,6 +722,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
>              errno = ENOMEM;
>              host_addr = MAP_FAILED;
>          }
> +#endif /* TARGET_ABI_BITS < TARGET_LONG_BITS */

Hm, Philippe, this will silence the clang error, but is this the right
thing to do?

Why do you think the case:

TARGET_ABI_BITS < TARGET_LONG_BITS

doesn't need this check? In any case, for clarity, the reason should
be mentioned in the commit message.

Regards,
Aleksandar


>      }
>
>      if (host_addr == MAP_FAILED) {
> --
> 2.21.3
>
>