#1339: Memory alignment in CarpetLib failing ---------------------+------------------------------------------------------ Reporter: rhaas | Owner: eschnett Type: defect | Status: new Priority: minor | Milestone: Component: Carpet | Version: Resolution: | Keywords: ---------------------+------------------------------------------------------

Comment (by eschnett):

I am testing a patch.

FYI: {{{ $ git diff diff --git a/Carpet/CarpetLib/src/mem.cc b/Carpet/CarpetLib/src/mem.cc index 89d8fb2..0a5f369 100644 --- a/Carpet/CarpetLib/src/mem.cc +++ b/Carpet/CarpetLib/src/mem.cc @@ -105,6 +105,7 @@ mem (size_t const vectorlength, size_t const nelems, size_t const max_cache_linesize = get_max_cache_linesize(); size_t const vector_size = CCTK_REAL_VEC_SIZE * sizeof(T); size_t const alignment = align_up(max_cache_linesize, vector_size); + assert(alignment >= 1); // Safety check assert(alignment <= 1024); // Assume optimistically that operator new returns well-aligned @@ -123,7 +124,8 @@ mem (size_t const vectorlength, size_t const nelems, } else { allocate_with_alignment: // Operator new needs manual alignment - size_t const max_padding = alignment / sizeof(T) - 1; + size_t const max_padding = div_up(alignment, sizeof(T)) - 1; + assert((ptrdiff_t)max_padding >= 0); storage_base_ = new T [vectorlength * nelems + max_padding]; storage_ = (T*) (size_t(storage_base_ + max_padding) & ~(alignment-1)); assert(size_t(storage_) >= size_t(storage_base_ ) and }}}

(This corrects a rounding error, and adds more safety checks.)

#1339: Memory alignment in CarpetLib failing ---------------------+------------------------------------------------------ Reporter: rhaas | Owner: eschnett Type: defect | Status: new Priority: minor | Milestone: Component: Carpet | Version: Resolution: | Keywords: ---------------------+------------------------------------------------------

Comment (by eschnett):

New patch:

{{{ diff --git a/Carpet/CarpetLib/src/mem.cc b/Carpet/CarpetLib/src/mem.cc index 89d8fb2..be28d20 100644 --- a/Carpet/CarpetLib/src/mem.cc +++ b/Carpet/CarpetLib/src/mem.cc @@ -105,6 +105,7 @@ mem (size_t const vectorlength, size_t const nelems, size_t const max_cache_linesize = get_max_cache_linesize(); size_t const vector_size = CCTK_REAL_VEC_SIZE * sizeof(T); size_t const alignment = align_up(max_cache_linesize, vector_size); + assert(alignment >= 1); // Safety check assert(alignment <= 1024); // Assume optimistically that operator new returns well-aligned @@ -123,7 +124,8 @@ mem (size_t const vectorlength, size_t const nelems, } else { allocate_with_alignment: // Operator new needs manual alignment - size_t const max_padding = alignment / sizeof(T) - 1; + size_t const max_padding = div_up(alignment, sizeof(T)); + assert((ptrdiff_t(max_padding) >= 0); storage_base_ = new T [vectorlength * nelems + max_padding]; storage_ = (T*) (size_t(storage_base_ + max_padding) & ~(alignment-1)); assert(size_t(storage_) >= size_t(storage_base_ ) and }}}

Operator new's alignment may be less than the type's size (if a type requires alignment less than its size, such as e.g. complex numbers). Since we assume that a type's alignment is at least its size, we need to request more storage.