> On Apr 8, 2025, at 12:54, Siddhesh Poyarekar <siddh...@gotplt.org> wrote:
>
> On 2025-04-08 12:41, Qing Zhao wrote:
>> The gimple IR is:
>> 1 int main ()
>> 2 {
>> 3 int D.5072;
>> 4
>> 5 {
>> 6 struct annotated * q;
>> 7
>> 8 q = alloc_buf (10);
>> 9 _1 = __builtin_dynamic_object_size (q, 1);
>> 10 __builtin_printf ("the bdos whole is %d\n", _1);
>> 11 D.5072 = 0;
>> 12 return D.5072;
>> 13 }
>> 14 D.5072 = 0;
>> 15 return D.5072;
>> 16 }
>> 17
>> 18
>> 19 __attribute__((noinline))
>> 20 struct annotated * alloc_buf (int index)
>> 21 {
>> 22 struct annotated * D.5074;
>> 23 struct annotated * p;
>> 24 25 _1 = (long unsigned int) index;
>> 26 _2 = _1 + 9;
>> 27 _3 = MAX_EXPR <_2, 16>;
>> 28 p = malloc (_3);
>> 29 _4 = (long unsigned int) index;
>> 30 p->count = _4;
>> 31 D.5074 = p;
>> 32 return D.5074;
>> 33 }
>> When we generate the .ACCESS_WITH_SIZE for a pointer reference to “struct
>> annotated”,
>> Looks like all the pointer references, at line 8, “q”, at line 9, “q”, at
>> line 28, “p”, need to be changed
>> to a call to .ACCESS_WITH_SIZE. this might increase the IR size
>> unnecessarily. Might have some
>> Impact on the inlining decision heuristics or other heuristic that depend on
>> the code size.
>
> Do you need a .ACCESS_WITH_SIZE for initialization sites?
It’s not necessary. I will need to see how to distinguish an initialization
site from use sites in C FE.
> I was thinking we ought to need it only for read/dereference sites (which
> should be sufficient as a barrier too), so in this case it would only be for
> 'q' at line 9.
Will study a little bit more here to see how to implement this in FE.
>
>>> For a reference to a structure with FAM, such as p, we can generate a call
>>> to .ACCESS_WITH_SIZE whose 3rd argument
>>> is 0 (the number of bytes). And this information can be used in
>>> __builtin_object_size. But not in array bound sanitizer.
>
> Would that be necessary though, given that the array bound sanitizer only
> works on arrays and not other kinds of objects?
Yes, that’s my thought too.
Thanks for your suggestions. They are helpful.
Qing
>
> Thanks,
> Sid
