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Subject: Re: [PATCH 1/2] ArmPkg/AsmMacroIoLibV8: Introduce ASM_FUNC_ALIGN()
From: =?UTF-8?B?TWFydmluIEjDpHVzZXI=?= <mhaeuser@posteo.de>
In-Reply-To: <CAMj1kXEwutN2PyeNSCTPFQd3uV7zP0ZKA9ZYM803zvzOA7kdEA@mail.gmail.com>
Date: Tue, 18 Apr 2023 08:18:32 +0000
Cc: Leif Lindholm <quic_llindhol@quicinc.com>,
 edk2-devel-groups-io <devel@edk2.groups.io>,
 Ard Biesheuvel <ardb+tianocore@kernel.org>,
 Sami Mujawar <sami.mujawar@arm.com>,
 Vitaly Cheptsov <vit9696@protonmail.com>
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To: Ard Biesheuvel <ardb@kernel.org>
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> On 18. Apr 2023, at 10:10, Ard Biesheuvel <ardb@kernel.org> wrote:
>=20
> On Tue, 18 Apr 2023 at 08:40, Marvin H=C3=A4user <mhaeuser@posteo.de> =
wrote:
>>=20
>>=20
>>> On 17. Apr 2023, at 23:18, Ard Biesheuvel <ardb@kernel.org> wrote:
>>>=20
>>> Agree with all of this.
>>>=20
>>> And thanks for tracking this down - must not have been fun :-)
>>=20
>> No worries - it wasn=E2=80=99t. :) It was mere luck Vitaly discovered =
early it was an issue that triggered based on the binary layout rather =
than a bug in the mapping code itself=E2=80=A6
>>=20
>> Speaking of not fun to track down, I initially wanted to add ASSERTs =
(yes, runtime :( ) to check the alignment guarantee is actually met. =
Leif basically declined any form of regression-testing at runtime. Do =
you happen to have a simple(!) idea for how it could be checked at =
build-time? (It=E2=80=99s less about =E2=80=9Cwhich commands do I =
run?=E2=80=9D and more about integration with the build process / =
BaseTools, cross-OS compatibility, etc.)
>>=20
>=20
>=20
> I think we should just add another align to the code:
>=20
> .align xx
> func:
>=20
> < code >
>=20
> .align xx
> .org func + xx
>=20
> That way, if the code straddles a xx-aligned boundary, the .org will
> move backwards and force an error.

Wow, that's pretty fucking smart... I didn't even know that directive =
was a thing. I will try to toy with it soon. Do you want it as a =
separate series, separate commit in the current series, or squashed into =
the fix?=