Re: [PATCH] BaseTools/tools_def: use separate PP definition for DTC

[Leif Lindholm <leif.lindholm@linaro.org>]

On Tue, Feb 27, 2018 at 07:02:06PM +0000, Ard Biesheuvel wrote:
> On 27 February 2018 at 18:58, Leif Lindholm <leif.lindholm@linaro.org> wrote:
> > On Tue, Feb 27, 2018 at 06:36:08PM +0000, Ard Biesheuvel wrote:
> >> On 27 February 2018 at 18:33, Leif Lindholm <leif.lindholm@linaro.org> wrote:
> >> > On Tue, Feb 27, 2018 at 05:51:32PM +0000, Ard Biesheuvel wrote:
> >> >> Clang's preprocessor behaves differently from GCC's, and produces
> >> >> intermediate device tree source that still contains #pragma pack()
> >> >> and other directives that the device tree compiler chokes on.
> >> >>
> >> >> For assembling device tree sources, it matters very little which
> >> >> preprocessor is being used, so let's just use GNU CPP explicitly.
> >> >
> >> > Ah, right, same fundamental issue as
> >> > 5b8766bb92debfa7b2f45a4a6d683b4227360d66.
> >>
> >> Yes, and I fail to see why changing just those two files makes a
> >> meaningful difference.
> >
> > Probably because Secure96Dxe.inf has a lot more [Packages] and
> > [LibraryClasses] dependencies than DeveloperBox.inf.
> >
> > This patch would undoubtedly also have resolved that issue.
> > (As would clang preprocessor not throwing out C syntax when explicitly
> > asked to provide asm.)
> >
> >> > However, this time triggered by autogen seemingly forcing inclusion of
> >> > lots of central header files that are not even used, like
> >> > MdePkg/Include/IndustryStandard/Bluetooth.h
> >> > MdePkg/Include/IndustryStandard/Acpi10.h
> >> > and so on.
> >> >
> >> > Is there any way to suppress these implicit includes from .dts
> >> > processing?
> >>
> >> There is 'Trim', which can filter #include'd content, but using that
> >> also robs us of the ability to #include .dtsi files, which was kind of
> >> the point of using the preprocessor in the first place.
> >
> > Yeah, that'd definitely be missing the point slightly.
> >
> > I was thinking more along the lines of either excluding the autogen
> > bits from the preprocessing or using a separate .inf for the .dts.
> >
> 
> We need the AutoGen.h bits for the fixed PCD values, which was the
> other reason for using the preprocessor in the first place.

Yeah, I was afraid of that.

> Separate .inf would mean registering file GUIDs in the package .DEC,
> so that the driver can find the binary image at runtime, which is what
> I was trying to get away from by pulling it into the driver,
> especially because we are dealing with overlay DT snippets, of which
> there may be many, rather than a single DT (with a well known file
> GUID) for the entire platform.
>
> > If neither of those feels practical, the proposed patch is fine.
> > It just feels a little bit clunky.
> 
> Yeah, I don't see any unclunky solutions, unfortunately.

Fair enough.
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>