On 2023-10-25 09:27, Qing Zhao wrote:
On Oct 24, 2023, at 7:56 PM, Siddhesh Poyarekar <siddh...@gotplt.org> wrote:
On 2023-10-24 18:51, Qing Zhao wrote:
Thanks for the proposal!
So what you suggested is:
For every x.buf, change it as a __builtin_with_size(x.buf, x.L) in the FE,
then the call to the _bdos (x.buf, 1) will
Become:
_bdos(__builtin_with_size(x.buf, x.L), 1)?
Then the implicit use of x.L in _bdos(x.buf.1) will become explicit?
Oops, I think Martin and I fell off-list in a subthread. I clarified that my
comment was that any such annotation at object reference is probably too late
and hence not the right place for it; basically it has the same problems as the
option A in your comment. A better place to reinforce such a relationship
would be the allocation+initialization site instead.
I think Martin’s proposal might work, it’s different than the option A:
A. Add an additional argument, the size parameter, to __bdos,
A.1, during FE;
A.2, during gimplification phase;
Option A targets on the __bdos call, try to encode the implicit use to the
call, this will not work when the real object has not been instantiation at the
call site.
However, Martin’s proposal targets on the FMA array itself, it will enhance the
FAM access naturally with the size information. And such FAM access with size
info will propagated to the __bdos site later through inlining, etc. and then
tree-object-size can use the size information at that point. At the same time,
the implicit use of the size is recorded correctly.
So, I think that this proposal is natural and reasonable.
Ack, we discussed this later in the thread and I agree[1]. Richard
still has concerns[2] that I think may be addressed by putting
__builtin_with_size at the point where the reference to x.buf escapes,
but I'm not very sure about that.
Oh, and Martin suggested using __builtin_with_size more generally[3] in
bugzilla to address attribute inlining issues and we have high level
consensus for a __builtin_with_access instead, which associates access
type in addition to size with the target object. For the purposes of
counted_by, access type could simply be -1.
Thanks,
Sid
[1]
https://inbox.sourceware.org/gcc-patches/73af949c-3caa-4b11-93ce-3064b95a9...@gotplt.org/T/#m4f3cafa489493180e258fd62aca0196a5f244039
[2]
https://inbox.sourceware.org/gcc-patches/73af949c-3caa-4b11-93ce-3064b95a9...@gotplt.org/T/#mcf226f891621db8b640deaedd8942bb8519010f3
[3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96503#c6
