[LEDE-DEV] Adding new targets/subtargets

[Yousong Zhou]

On 31 December 2016 at 06:13, Philip Prindeville
<philipp_subx at redfish-solutions.com> wrote:
>
>> On Dec 29, 2016, at 7:46 PM, Yousong Zhou <yszhou4tech at gmail.com> wrote:
>>
>> On 30 December 2016 at 03:29, Philip Prindeville
>> <philipp_subx at redfish-solutions.com> wrote:
>>> On Dec 28, 2016, at 7:57 PM, Yousong Zhou <yszhou4tech at gmail.com> wrote:
>>>
>>> The x86/64/config-default is missing the following switches:
>>>
>>> CONFIG_MCORE2=y
>>> CONFIG_MDIO=y
>>> CONFIG_X86_USE_PPRO_CHECKSUM=y
>>>
>>> otherwise they should be identical (unless I’ve overlooked other values which are needed).
>>>
>>
>> Well, it seems that the built kernel with CONFIG_MCORE2 set may not
>> run on other older x86_64 cpus as it will enable -march=core2
>> optimisation flag.  "make kernel_menuconfig" can be used to select
>> those symbols.   But I think they are not appropriate to go into
>> x86/64 subtarget, yet adding another subtarget for such minor diff
>> seems overkill.
>
>
> That actually might not be optimized enough.  The appliance that I’m targeting does a lot of crypto, so enabling the Xeon-specific AES operations should help a lot with AES-CBC and AES-EBC sessions.
>

Well, I think the build system should be flexible enough to allow you
to do such customisations.


>>>> I cannot find direct reference to ARCH_PACKAGES in target/ dir.  I
>>>> think it's a string intended to represent the arch of packages built
>>>> for current target/subtarget.  Previously in OpenWrt, we build
>>>> packages like pppd separately for targets like ramips and ar71xx, even
>>>> though they are of the same arch "mips_24kc" (there was a time ar71xx
>>>> was optimized for 34kc though).  Now these packages are arch-specific
>>>> and will reside in dir bin/packages/<CONFIG_TARGET_ARCH_PACKAGES>.
>>>
>>> Doing the following:
>>>
>>> openwrt$ grep -r -n -E -e ‘\<ARCH\>' -e ‘\<ARCH_PACKAGES\>’ include/ target/
>>> include/image.mk:122:   mkimage -A $(ARCH) -O linux -T kernel -C $(1) -a $(2) -e $(3) \
>>
>> <snip>
>>
>>>
>>>
>>> so it seems to be used for a few different things including image naming.  ARCH also seems to be overloaded, from what I can tell…
>>>
>>> ARCH_SUFFIX is taken from CONFIG_CPU_TYPE, but in my setup that value seems to have been set to “ “ which I can’t say I understand.
>>>
>>
>> CPU_TYPE is mainly used for forming compiler optimisation flags.  It's
>> empty for x86_64 because LEDE does not have specific flags for the
>> arch yet.
>>
>> BTW. now sure how OpenWrt repo goes these days, but I guess build
>> system of LEDE is likely to has received more care than the OpenWrt
>> one.  So it's worth a try.
>
>
>
> How does CPU_TYPE end up affecting the CFLAGS that are used to compile both target/ and packages/ ?  The settings for CONFIG_TARGET_OPTIMIZATION seem pretty generic.

Take a look at include/target.mk, CPU_CFLAGS_$(CPU_TYPE) will form
part of the default cflags and these are used to do release builds.
CONFIG_TARGET_OPTIMIZATION can be used to override that when you are
building on your own.

>>>>> Is there any unofficial documentation (i.e. not on the wiki) about how to go about adding platforms?
>>>>>
>>>>> There’s a wiki entry on “adding a new device” but doesn’t seem to be applicable to what I’m doing.
>>>>>
>>>>> Any pointers are appreciated.
>>>>
>>>> Adding target/subtarget does not happen very often, but the build
>>>> system changes a lot in various aspects.  Probably nobody bothers to
>>>> add such doc.  But we can always consult git log/mail history to see
>>>> how previous ones are added.
>>>>
>>>>               yousong
>>>
>>>
>>> Actually, all the subtargets have been purged, from what I can tell.  I don’t see any subtargets (just profiles?) so I don’t even know if the subtarget machinery is still intact or not.
>>>
>>> -Philip
>>>
>>
>> Hmm, not sure I understand your concern about this one.  Subtarget
>> machinery is certainly still there as all these
>> x86/{generic,64,legacy} subtargets at least still build.
>>
>>                yousong
>
>
> I noticed that in Openwrt a lot of the x86 subtargets (alix, geos, net5501) had gone away (well, been combined into a generic “geode” image).
>
> -Philip
>

I can only guess it's very likely for the purpose of saving buildbot
resources.  But I never played those subtargets myself and have no
idea whether they still work (they should though)

                yousong