Re: [PATCH 2/3] ARM/Assembler: Correct syntax from RVCT for MSFT

["Ard Biesheuvel" <ard.biesheuvel@linaro.org>]

On Thu, 19 Sep 2019 at 14:25, Leif Lindholm <leif.lindholm@linaro.org> wrote:
>
> On Thu, Sep 19, 2019 at 01:53:35PM +0300, Ard Biesheuvel wrote:
> > > > I mean that I'd prefer to assemble the .asm files in ARM mode,
> > > > especially since I am not convinced that the startup code we have is
> > > > guaranteed to switch into the right mode after the CPU comes out of
> > > > reset in ARM mode.
> > >
> > > That could be resolved with a trivial branch at that point (or just
> > > forcing ARM for the whole entry file) though.
> > >
> >
> > Of course.
> >
> > The problem is that the first branch instruction is patched into the
> > FV files by the BaseTools, and so the startup code is entered in ARM
> > mode by default.
> >
> > So that means we'll either have to
> > 1) switch to ARM mode
> > 2) emit one branch instruction
> > 3) switch back to Thumb mode
>
> I was thinking more like tying down the entry function (or as I said,
> the whole file) as ARM, then letting the toolchain decide for the bits
> where we don't have instuction-set dependent ABIs.
>
> > 4) fix up all the code so it assembles in Thumb mode
>
> Which is what Baptiste has done in this set.
>
> > 1) switch to ARM mode
>
> In all 48 files (+3 in edk2-platforms), or just the ones where not
> doing so triggers build errors? Currently.
>
> I'm OK with restricting ourselves to just setting ARM in the
> triggering files for simplicity, especially in order to streamline the
> toolchain migration from RVCT to VS (and the subsequent purge of PVCT
> support). I'm not seeing it as a solution.
>

As long as we align the .asm files with the .S files, I am fine with
that. And since we focus on v7+ only these days, I'm fine with
changing existing ARM files to Thumb2.

What I don't want is a situation where the toolchain's default decides
how code is assembled, since that means you have to test all your code
changes twice.