Draft for moving network headers from RTEMS to newlib

[Chris Johns]

On 26/04/2016 19:26, Sebastian Huber wrote:
>
>
> On 26/04/16 10:27, Chris Johns wrote:
>> On 26/04/2016 17:31, Sebastian Huber wrote:
>>> On 26/04/16 07:51, Chris Johns wrote:
>>>> On 26/04/2016 01:06, Christian Mauderer wrote:
>>>>> currently we try to remove the network specific POSIX headers from
>>>>> RTEMS. Instead, we add current headers from FreeBSD to newlib. This
>>>>> will
>>>>> simplify the build process of some libraries that depend on the
>>>>> network
>>>>> (like LibreSSL).
>>>>
>>>> What does this work flow offer over building and installing an RTEMS
>>>> kernel for a BSP and adding that path to the packages include paths?
>>>
>>> You don't build per BSP in this scenario. You build per multilib and
>>> have only one set of header files installed.
>>
>> Hmm multilib, this is what I thought was happening. I see this
>> exploding the libraries if packages are built this way. Do we manage
>> this or not bother and just accept all variants have to be built?
>
> The multilibs are there for a purpose. In case a particular architecture
> has superfluous multilibs, then we should remove them.

I have no idea which variants of each architecture are actually used. I 
suspect we need to document this better.

I see clang has better support for multilib than in the past ...

$ clang -print-multi-lib
.;
x86_64;@m64

This is nice.

> I see an
> explosion of libraries if we build them for each BSP. We have count of
> BSPs > count of multilibs, otherwise the GCC configuration is broken.

This is only valid for developers who have to build all BSPS. Most uses 
have one or maybe 2 BSPs they are working with at a time.

My question was, do we care about this? You do not see it as an issue 
because your need to package built tools and libraries is important, and 
I can live with it cause I have fast machines and fast disks but we are 
just 2 people.

FYI there are 11 variants in ARM.

>
>>
>>> You are able to use the
>>> network header files during GCC build, which makes it easier to build
>>> the run-time libraries of Ada and Go.
>>
>> Nice. Maybe limiting what is added to just building languages would be
>> a nice first starting point.
>>
>>>
>>>>
>>>> How do you get the flags for the compiler to build the package?
>>>
>>> See attached script which builds for example libpng for all multilibs.
>>
>> Multilibs has not had a very successful history with RTEMS (outside of
>> gcc). They are not very user friendly and are a source of questions
>> and issues.
>
> I think multilibs are great for libraries which don't depend on BSP
> specifics.

I know ...

https://lists.rtems.org/pipermail/users/2012-February/024544.html

:)

It is a useful idea and I like the work being done with the standards 
based headers.

There is something inconsistent about this I am yet to put my finger on. 
I suspect it is related to some libraries being multilib and some 
libraries not being multilib. Consider an example app and lets assume 
all packages are working perfectly ..

1) GCC, newlib.  - Multilib,   /bd/rtems/4.11.0
2) RTEMS         - Specific,   /bd/rtems/4.11.0/bsps
3) NTP           - Multilib,   /bd/rtems/4.11.0/bsps
4) Protobufs     - Multilib,   /bd/rtems/4.11.0/bsps
5) Civetweb      - Multilib,   /bd/rtems/4.11.0/bsps
6) NetSNMP       - Specific,   /bd/rtems/4.11.0/bsps
7) Application   - Executable

I wonder what the application linker command line looks like?

Does gcc's multilib search extend beyond it's own install base?

The NetSNMP package is put here as Specific because it uses a large 
number of platform specific header files to access things like 
interfaces and routing tables.

My point is, when a user considers 3rd party packages they have moved to 
the specific requirements for a specific project and multilibs verses 
per BSP builds mean little. The multilib view is nice when viewed from 
the RTEMS developer perspective or someone providing a service to 
clients where they bundle packages as prebuilt libraries, but is it nice 
to users from the community? I do not know. If both multilib and 
specific libraries can coexist I have no issue but this needs to be shown.

Note, the layout is based on the Project Sandboxing documentation I have 
in the Getting Started Guide 
(https://ftp.rtems.org/pub/rtems/people/chrisj/docs/user/start/index.html#project-sandboxing). 
This documentation would need to be updated (hint).

> What is the benefit of per BSP libpng for example?

What is built is tested, there is a 1:1 relationship here. The user is 
able to see and understand what is built, where it is installed and what 
they are linking too. Multilibing packages adds a layer of indirection 
and with that extra complexity.

Multilibs in gcc is not very user friendly ....

$ i386-rtems4.11-gcc -print-multi-lib
.;
m486;@mtune=i486
mpentium;@mtune=pentium
mpentiumpro;@mtune=pentiumpro
soft-float;@msoft-float
m486/soft-float;@mtune=i486 at msoft-float

$ arm-rtems4.11-gcc -print-multi-lib
.;
thumb;@mthumb
thumb/armv6-m;@mthumb at march=armv6-m
thumb/armv7-a;@mthumb at march=armv7-a
thumb/armv7-r;@mthumb at march=armv7-r
thumb/armv7-m;@mthumb at march=armv7-m
thumb/armv7-a/neon/hard;@mthumb at march=armv7-a at mfpu=neon at mfloat-abi=hard
thumb/armv7-r/vfpv3-d16/hard;@mthumb at march=armv7-r at mfpu=vfpv3-d16 at mfloat-abi=hard
thumb/armv7-m/fpv4-sp-d16/hard;@mthumb at march=armv7-m at mfpu=fpv4-sp-d16 at mfloat-abi=hard
eb/thumb/armv7-r;@mbig-endian at mthumb@march=armv7-r
eb/thumb/armv7-r/vfpv3-d16/hard;@mbig-endian at mthumb@march=armv7-r at mfpu=vfpv3-d16 at mfloat-abi=hard

I have no idea what this all means.

>
>>
>> I would like to see something more than a script posted before I get
>> excited and accepting of this path. I would like to understand the
>> work flow for the project, the developers and the users?
>>
>>> You don't need BSPs installed to do this. The libpng is just an add-on
>>> to the tool chain.
>>
>> Sure, I understand this and it is nice. I hope users do not forget to
>> build the BSP. ;)
>
> The work flow is build the tool chain, build all support libraries you
> are interested in, then build the actual BSPs.

I was hoping for a specific plan for RTEMS, for developers and for users.

Does this mean you, Joel, and I all have personal scripts to build these 
things? Where does this get documented for users?

>
>>
>>>
>>>>
>>>> How are any tests present in the package built and linked?
>>>
>>> Tests are executables, so they need a BSP.
>>>
>>
>> Yes, so how do these packages get tested?
>
> How are packages tested currently?
>
> You can only test using a particular BSP.
>
>>
>>>>
>>>> Do we risk limited the functionality of a package by restricting the
>>>> headers exposed to only standards based headers? There are headers
>>>> which some packages use that will not be present.
>>>
>>> In case a common header file is missing for a particular package, then
>>> we can add this file to Newlib.
>>>
>>
>> If a package changes or something happens we would need a new version
>> of tools.
>
> Yes, but this area is not really volatile. Its not that we have a new
> POSIX standard every two months. The old network stack uses about 20
> year old header files.

Ok so this is only for standards base headers? I agree to this.

>
>> I am concerned about the management of the detail here and finding a
>> suitable set of headers for all packages across all architecture may
>> become complicated if there are incompatibilities between
>> architectures and/or packages. With standards based headers we have
>> the standard to fall back on and we can get the package fixed. When we
>> move away from standards based headers we open up a range potential
>> issue. Adding the headers is easy, removing would be hard if not
>> impossible. Once we head down this path will be difficult to turn back.
>
> The place of the header file makes no difference here. For the user its
> the same if you remove the file from Newlib or RTEMS.
>
>>
>> It is a massive task to get the tools to build for supported
>> architectures _now_ and I hope this path does not increase the work
>> load here.
>
> If we add Ada and Go to the standard languages, then it could get more
> difficult.
>

This is understood.

>>
>> Do you have limits or boundaries for suitable headers? Who administers
>> these boundaries?
>>
>> What is the procedure for a user to add a header?
>
> Like everything else in RTEMS this will be user driven. Someone is not
> satisfied with the current situation and will work out a fix.
>
>>
>> If a header is missing does this means the user cannot build a
>> package? In other words can we mix how we currently build packages
>> with this way of building packages?
>
> You can still build against a BSP which presents the full set of header
> files.

Great.

>
>>
>>>>
>>>>> Further it will be another step into the direction of
>>>>> extracting the old RTEMS network stack and build it as an independent
>>>>> package.
>>>>
>>>> Is this just a specialised version of the generic vertical integration
>>>> problem being discussed in the civetweb thread?
>>>>
>>>> I am not against standards based headers like the ones being discussed
>>>> here being move to newlib however I currently do not see what the
>>>> advantage is and how value is being adding over a specific build order
>>>> of packages.
>>>
>>> Building libraries against a particular BSP using actually BSP
>>> independent header files is not really a great overall setup.
>>
>> Correct each BSP is independent and that gives me the ability to vary
>> and change things in RTEMS without needing to repeat tools builds or
>> create separate sandboxes at the tools level. The whole point of the
>> cpukit was to multilib build the generic code and avoid the
>> duplication in the BSPs however in the end it became clear a single
>> specific BSP is all most users need and overhead of that specific
>> build and install even with per BSP headers is faster and simpler than
>> the whole multilib path.
>>
>> Having a single tree of headers is fine if they are stable and not
>> changing. I do not use a single prefix and prefer separate prefixes so
>> I can mix and match and play. Having more and more header become part
>> of the tools removes an important part of this process.
>>
>> It comes down to the type of header and how often they change.
>
> How often do standard header files change? Its much more likely that a
> tool chain update happens due to a GCC release or configuration change.

A lot lately. ;)

>
>>
>>>
>>>>
>>>> I still see all the normal issues of CFLAGS, LDFLAGS, 3rd party
>>>> package dependence still being present once this work is completed.
>>>
>>> For libraries, the LDFLAGS are irrelevant.
>>
>> What about testing? This needs to be resolved.
>
> Yes, this needs to be resolved, but we cannot fix all problems at once.

This is understood and not what I expect or what I am asking for.

> We have to start somewhere. Moving the standard network header files to
> Newlib gives us the ability to
>
> * more easily build the run-time libraries for Ada and Go,

+1

> * provide one set of header files for use with three different network
> stacks (old, libbsd, lwIP),

+1

> * in case we share these header files with Cygwin, then they are exposed
> to a large set of packages, and
> * enable multilib based builds for network support libraries like SSL,
> HTTP server.

+/-0 (don't care if both approaches work)

>
>>
>>> One advantage is that the
>>> built-in search paths are sufficient if you build against a multilib
>>> (except the machine flags), see attached script.
>>
>> This assumes you install everything under the one prefix. Unless you
>> are on a production build I do not recommend this. If you are building
>> and installing different libraries under different prefixes you are
>> back at the same issue of handling include paths so include paths will
>> always need to work.
>>
>> Please understand I am not against this, I would just like the all
>> detail exposed and understood.
>>
>> Chris
>
> I don't understand why you need these libraries per BSP if they have
> absolutely no BSP dependency. I use these multilib based libraries for
> several years and it works quite well.

Great to hear and I am sure these changes will make your private efforts 
simpler.

I am attempting to understand what effect this has on the RTEMS project 
and our users. If you are able to build the existing 3rd party packages 
in the RSB before and after the changes then I am happy. Some may not 
build completely so if you can achieve the same level of build that 
would be fine. I would also like to see some documentation about 
multilibing and how users are able to use it and do this themselves.

Chris