Re: [edk2-devel] Expansion of ARCH in .dsc files

["Joey Vagedes via groups.io" <joeyvagedes=microsoft.com@groups.io>]

Leif,

For your awareness, Section 3.4 of the INF specification states that architectural modifiers for the [Defines] section tag are not permitted.

So that you can Ctrl+F and to find the exact language, here is a quote:

"architectural modifiers for the [Defines] section tag are not permitted"

https://tianocore-docs.github.io/edk2-InfSpecification/release-1.27/3_edk_ii_inf_file_format/34_[defines]_section.html#34-defines-section

Thanks,
Joey

-----Original Message-----
From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Leif Lindholm via groups.io
Sent: Tuesday, January 7, 2025 11:05 AM
To: devel@edk2.groups.io
Cc: Ajan Zhong <ajan.zhong@newfw.com>; Ard Biesheuvel <ardb+tianocore@kernel.org>; Kinney, Michael D <michael.d.kinney@intel.com>
Subject: [EXTERNAL] [edk2-devel] Expansion of ARCH in .dsc files

So... I originally tripped over my misunderstanding of <subject> when writing
https://github.com/tianocore/edk2/pull/6262 to get around something I wanted to test in UefiPayloadPkg.

Now Ajan has run into at least an adjacent problem when trying to rework
https://github.com/tianocore/edk2/pull/6545 based on feedback I among others provided.

Now, the thing I had misunderstood before is that when build is called with multiple -a options, the ARCH variable will expand to a space-separated list of *all* the specified architectures.
A lot of Arm/AArch64 modules assume this variable only ever contains a single architecture.

The thing is, I don't think this is clearly documented in the .dsc specification at all. And it is frequently used as a shorthand in there in a form that would only work if build was called with a single -a.
Now, this also means that there are nearly no correct users of ARCH in
edk2 or edk2-platforms.
Because "the list of all architectures being built simultaneously"
simply isn't very useful information
build-time. There are two correct uses in edk2, in EmulatorPkg.dsc and in UefiPayloadPkg.dsc, using '!if "IA32" in "$ARCH"', which as far as I can tell is the only possible way to use the variable correctly.
Slightly amusingly, EmulatorPkg.dsc also contains an incorrect use.

I guess the behaviour is a direct result of how the build command is architected.
I guess the one question I have is - is this the intended behaviour?

Ard: I think we need to update some of our .dsc files...

Ajan: one somewhat hacky workaround I can think of to separate the output images is to hardcode the output image name in arch-specific Defines sections, like so:

diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc index 0bd8d85cab03..f07f2b91764e 100644
--- a/ArmVirtPkg/ArmVirtQemu.dsc
+++ b/ArmVirtPkg/ArmVirtQemu.dsc
@@ -12,12 +12,17 @@
 # Defines Section - statements that will be processed to create a Makefile.
 #
 ################################################################################
+[Defines.ARM]
+  OUTPUT_DIRECTORY               = Build/ArmVirtQemu-ARM
+
+[Defines.AARCH64]
+  OUTPUT_DIRECTORY               = Build/ArmVirtQemu-AARCH64
+
 [Defines]
   PLATFORM_NAME                  = ArmVirtQemu
   PLATFORM_GUID                  = 37d7e986-f7e9-45c2-8067-e371421a626c
   PLATFORM_VERSION               = 0.1
   DSC_SPECIFICATION              = 0x00010005
-  OUTPUT_DIRECTORY               = Build/ArmVirtQemu-$(ARCH)
   SUPPORTED_ARCHITECTURES        = AARCH64|ARM
   BUILD_TARGETS                  = DEBUG|RELEASE|NOOPT
   SKUID_IDENTIFIER               = DEFAULT







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