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[C++] Rare bad buffer content alignment if sizeof(T) != alignof(T) (#7520)

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* [C++] Add a failing unit test for #7516 (Rare bad buffer content alignment if sizeof(T) != alignof(T))

* [C++] Fix final buffer alignment when using an array of structs
* A struct can have an arbitrary size and therefore sizeof(struct) == alignof(struct)
  does not hold anymore as for value primitives.
* This patch fixes this by introducing alignment parameters to various
  CreateVector*/StartVector calls.
* Closes #7516
This commit is contained in:
Denis Blank
2022-09-21 20:05:05 +02:00
committed by GitHub
parent bfceebb7fb
commit 72aa85a759
10 changed files with 611 additions and 16 deletions
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4
src/idl_parser.cpp
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@@ -1614,6 +1614,7 @@ CheckedError Parser::ParseVector(const Type &type, uoffset_t *ovalue,
});
ECHECK(err);
const size_t alignment = InlineAlignment(type);
const size_t len = count * InlineSize(type) / InlineAlignment(type);
const size_t elemsize = InlineAlignment(type);
const auto force_align = field->attributes.Lookup("force_align");
@@ -1623,7 +1624,8 @@ CheckedError Parser::ParseVector(const Type &type, uoffset_t *ovalue,
if (align > 1) { builder_.ForceVectorAlignment(len, elemsize, align); }
}
builder_.StartVector(len, elemsize);
// TODO Fix using element alignment as size (`elemsize`)!
builder_.StartVector(len, elemsize, alignment);
for (uoffset_t i = 0; i < count; i++) {
// start at the back, since we're building the data backwards.
auto &val = field_stack_.back().first;