[llvm-dev] A struct {i8, i64} has size == 12, clang says size 16

[Reid Kleckner via llvm-dev]

It sounds like your DataLayout may not match clang's for x86_64-linux. What
does it say about the alignment of i64?
On Wed, Apr 18, 2018 at 12:05 PM edA-qa mort-ora-y via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I'm creating a struct of `{i8,i64}` and `DataLayout::getTypeAllocSize`
> is returning `12`. `getStructLayout` also gives an `4` offset for the
> second element.

> The native ABI, and clang, for the same type are producing a size of 16,
> with an alignment of 8, for the second element.

> This is for the system triple "x86_64-linux-gnu"

> What could be causing this difference in alignment and how can I fix it?


> I'm verifying the native ABI with:

>      // clang -emit-llvm ll_struct_arg.c -S -o /dev/tty
>      #include <stddef.h>

>      typedef struct vpt_data {
>          _Bool c;
>          long int b;
>      } vpt_data;

>      int main() {
>          vpt_data v;
>          vpt_test(v);
>          auto a = sizeof(v);
>          auto off = offsetof(vpt_data,b);
>      }


> 16 is stored to `a` and 8 to `off`.

> --
> edA-qa mort-ora-y
>          http://mortoray.com/

> Creator of the Leaf language
>          http://leaflang.org/

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