Re: [PATCH bpf-next 2/2] selftests/bpf: Match tests against regular expression.

[Cupertino Miranda <cupertino.miranda@oracle.com>]

Alexei Starovoitov writes:

> On Thu, Jun 6, 2024 at 3:51 AM Cupertino Miranda
> <cupertino.miranda@oracle.com> wrote:
>>
>> GCC will allocate variables in a different order then clang and when
>> comparing content is not where comparisson is expecting.
>>
>> Some other test, would expect that struct fields would be in some
>> particular order, while GCC decides it would benefit from reordering
>> struct fields. For passing those tests I need to disable GCC
>> optimization that would make this reordering.
>> However reordering of the struct fields is a perfectly valid
>> optimization. Maybe disabling for this tests is acceptable, but in any
>> case the test itself is prune for any future optimizations that can be
>> added to GCC or CLANG.
>
> Not really.
> Allocating vars in different order within a section is fine,
> but compilers are not allowed to reorder fields within structs.
> There is a plugin for gcc that allows opt-in via
> __attribute__((randomize_layout)).
> But never by default.

Apologies for the mess up. Indeed the reordering happens on variable
declarations. In prog/test_core_autosize.c, it declares variables and in
prog_tests/core_autosize.c it checks content with a "template" struct
that should map how the data is layout in memory.
Somehow I miss remembered the actual problem and got confused with what
was actually being reorderd.

In the end both examples are the same.