[Bug sanitizer/59061] Port leaksanitizer

[kcc at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59061

--- Comment #32 from Kostya Serebryany <kcc at gcc dot gnu.org> ---
(In reply to Sergey Matveev from comment #31)
> (In reply to Kostya Serebryany from comment #30)
> > lsan's allocator clears all memory using internal_memset, which is damn
> > slow. (sets on byte at a time)
> > 
> > asan's allocator doesn't do that (it sets first 4K bytes of allocated region
> > with garbage using the REAL fast memset)
> > 
> > I think the right solution is to finally implement *fast* internal_memset. 
> > We'll do that. 

Some improvement made in 
http://llvm.org/viewvc/llvm-project?view=revision&revision=195549
Will reach gcc with the next merge. 


> > 
> > Sergey, can this difference between asan and lsan allocators cause 
> > false negatives/positives in lsan?
> 
> It can cause a false negative if there's a stale pointer outside of those
> 4k. But in practice 4k ought to be enough for anybody.

lol :) 

> 
> I think standalone LSan should support the max_alloc_fill_size flag. 

Mmm. Maybe... 
max_alloc_fill_size in asan is there primarily to protect from filling huge
allocations coming from LargeMmapAllocator



>> I'll also change it to use real memset.

Using REAL(memset) in sanitizer_common may not be a great idea.
(first of all, you can't do it easily)
Anyway, my change above improved the situation quite a bit
(2x on a synthetic test)