Re: [PATCH v1 2/3] linux-user: deal with address wrap for ARM_COMMPAGE on 32 bit

[Alex Bennée]

Richard Henderson <richard.henderson@linaro.org> writes:

> On 5/27/20 3:05 AM, Alex Bennée wrote:
>> @@ -2145,7 +2145,7 @@ static uintptr_t pgd_find_hole_fallback(uintptr_t 
>> guest_size, uintptr_t brk, lon
>>  
>>  /* Return value for guest_base, or -1 if no hole found. */
>>  static uintptr_t pgb_find_hole(uintptr_t guest_loaddr, uintptr_t guest_size,
>> -                               long align)
>> +                               long align, uintptr_t offset)
>>  {
>>      GSList *maps, *iter;
>>      uintptr_t this_start, this_end, next_start, brk;
>> @@ -2171,7 +2171,7 @@ static uintptr_t pgb_find_hole(uintptr_t guest_loaddr, 
>> uintptr_t guest_size,
>>  
>>          this_end = ((MapInfo *)iter->data)->start;
>>          next_start = ((MapInfo *)iter->data)->end;
>> -        align_start = ROUND_UP(this_start, align);
>> +        align_start = ROUND_UP(this_start + offset, align);
>>  
>>          /* Skip holes that are too small. */
>
> I suppose offset is supposed to mean we start from -offset?

Well guest_base will start higher meaning we have space for the
commpage beneath it.

> You didn't update
> pgb_find_hole_fallback.

Fixed.

>
>> -            loaddr = ARM_COMMPAGE & -align;
>> +            offset = (128 * KiB);
>
> Why 128K?  Surely this should be an expression against ARM_COMMPAGE.

In theory:

            offset = -(ARM_COMMPAGE & -align);

should do the trick but I found it failed every now and again.
Frustratingly putting printfs in made it go away so in frustration I
just upped the offset until it stopped happening.

I do kinda wish rr worked on i386 :-/


>
>
> r~


-- 
Alex Bennée