Re: [PATCH v4] linux-user: Add close_range() syscall

[Richard Henderson <richard.henderson@linaro.org>]

On 10/25/22 11:39, Helge Deller wrote:
> On 10/25/22 00:39, Richard Henderson wrote:
>> On 10/25/22 06:43, Helge Deller wrote:
>>> +            abi_long maxfd = arg2;
>>> +
>>> +            if ((sizeof(abi_long) == 4 && arg2 == (abi_long)0x7FFFFFFFUL) ||
>>> +                (sizeof(abi_long) == 8 && arg2 == (abi_long)0x7FFFFFFFFFFFFFFFULL)) {
>>> +                maxfd = target_fd_max;
>>> +            }
>>> +
>>> +            for (fd = arg1; fd < maxfd; fd++) {
>>
>> Why do we need explicit checks for INT32/64_MAX?
>> If the guest passes 0x7FFFFFFFFFFFFFFEULL,
> 
> A 32-bit guest (on a 64bit host) will pass 0x7FFFFFFFUL...
> 
>> do we really need to iterate over all of those impossible values?
> 
> The compiler will optimize one of those checks away, so it's effectively
> just one expression.

By impossible values, I mean all descriptors above target_fd_max.
The compiler will most certainly not optimize the number of loop iterations.


r~