Re: [Xen-devel] [PATCH 2/2] hvmloader: cast to 64bit before multiplication in get_module_entry

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.08.16 at 12:09, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 19/08/16 09:31, Jan Beulich wrote:
>>>>> On 19.08.16 at 10:06, <wei.liu2@xxxxxxxxxx> wrote:
>>> --- a/tools/firmware/hvmloader/hvmloader.c
>>> +++ b/tools/firmware/hvmloader/hvmloader.c
>>> @@ -272,8 +272,8 @@ const struct hvm_modlist_entry *get_module_entry(
>>>  
>>>      if ( !modlist ||
>>>           info->modlist_paddr > UINTPTR_MAX ||
>>> -         (info->modlist_paddr + info->nr_modules * sizeof(*modlist) - 1)
>>> -            > UINTPTR_MAX )
>>> +         (info->modlist_paddr +
>>> +          (uint64_t)info->nr_modules * sizeof(*modlist) - 1) > UINTPTR_MAX 
>>> )
>>>          return NULL;
>> This can be had without resorting to 64-bit multiplication, by bounds
>> checking
>>
>>          (UINTPTR_MAX - (uintptr_t)info->modlist_paddr) / sizeof(*modlist)
>>
>> instead. While we would certainly hope that compilers don't resort
>> to a libgcc helper for 64-bit multiplication, I think we'd better avoid
>> that risk altogether.
> 
> In this case, using libgcc would cause a link error because of
> -fno-builtin, so I don't think it is too bad.

And it's this link error which I want to avoid.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel