Re: [PATCH v1 04/10] linux-user: completely re-write init_guest_space

[Alex Bennée]

Thomas Huth <address@hidden> writes:

> On 13/05/2020 19.51, Alex Bennée wrote:
>> First we ensure all guest space initialisation logic comes through
>> probe_guest_base once we understand the nature of the binary we are
>> loading. The convoluted init_guest_space routine is removed and
>> replaced with a number of pgb_* helpers which are called depending on
>> what requirements we have when loading the binary.
>> 
>> We first try to do what is requested by the host. Failing that we try
>> and satisfy the guest requested base address. If all those options
>> fail we fall back to finding a space in the memory map using our
>> recently written read_self_maps() helper.
>> 
>> There are some additional complications we try and take into account
>> when looking for holes in the address space. We try not to go directly
>> after the system brk() space so there is space for a little growth. We
>> also don't want to have to use negative offsets which would result in
>> slightly less efficient code on x86 when it's unable to use the
>> segment offset register.
>> 
>> Less mind-binding gotos and hopefully clearer logic throughout.
>> 
>> Signed-off-by: Alex Bennée <address@hidden>
>> Acked-by: Laurent Vivier <address@hidden>
<snip>
>> +    } else {
>> +        if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
>> +            error_report("%s: requires more virtual address space "
>> +                         "than the host can provide (0x%" PRIx64 ")",
>> +                         image_name, (uint64_t)guest_hiaddr - guest_base);
>> +            exit(EXIT_FAILURE);
>>          }
>
>  Hi Alex,
>
> this causes an error with newer versions of Clang:
>
> linux-user/elfload.c:2076:41: error: result of comparison 'unsigned
> long' > 18446744073709551615 is always false
> [-Werror,-Wtautological-type-limit-compare]
> 4685         if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
> 4686             ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
> 4687 1 error generated.
>
> Any ideas how to fix this?

I guess this check only makes sense when abi_ulong > uintptr_t or IOW 64
bit guests running on 32 bit hosts. We could just wrap that check in:

#if HOST_LONG_BITS == 32

#endif

>
>  Thomas


-- 
Alex Bennée