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From: "Ard Biesheuvel" <ard.biesheuvel@linaro.org>
Date: Thu, 19 Sep 2019 13:53:35 +0300
Message-ID: <CAKv+Gu9S0g5BAC+PeN7AmFtaJvHJT37gGKr_qVksMSy076e3Dw@mail.gmail.com>
Subject: Re: [PATCH 2/3] ARM/Assembler: Correct syntax from RVCT for MSFT
To: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Baptiste Gerondeau <baptiste.gerondeau@linaro.org>, 
	edk2-devel-groups-io <devel@edk2.groups.io>, "Kinney, Michael D" <michael.d.kinney@intel.com>, 
	"Gao, Liming" <liming.gao@intel.com>, "Zhang, Shenglei" <shenglei.zhang@intel.com>, 
	Baptiste GERONDEAU <bgerondeau@gmail.com>
Content-Type: text/plain; charset="UTF-8"

On Thu, 19 Sep 2019 at 13:47, Leif Lindholm <leif.lindholm@linaro.org> wrote:
>
> On Thu, Sep 19, 2019 at 01:37:40PM +0300, Ard Biesheuvel wrote:
> > On Thu, 19 Sep 2019 at 13:34, Baptiste Gerondeau
> > <baptiste.gerondeau@linaro.org> wrote:
> > >> In any case, I'd strongly prefer it if the .S and .asm files produced
> > >> identical object code, so please apply the same changes to the sibling
> > >> .S files as well, please (but only the ones that are really required
> > >> when building it in ARM mode)
> > >
> > >
> > > ACK ! Will mirror changes to asm on S files (on separate commit, right ?)
> > > I'm only touching the files VS2019 as a problem with on the ARM
> > > build anyways (this is what you meant by "really required" right
> > > ?)
> >
> > 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
4) fix up all the code so it assembles in Thumb mode

or

1) switch to ARM mode


> But I'm OK with forcing ARM for all .asm files for now.
>

Indeed.