[PATCH 2/5] build: Use CSafeLoader if available

[Sebastian Huber]

On 03.05.23 05:30, Chris Johns wrote:
> On 28/4/2023 3:38 pm, Sebastian Huber wrote:
>> On 27.04.23 20:27, Gedare Bloom wrote:
>>> On Wed, Apr 26, 2023 at 11:46 PM Sebastian Huber
>>> <sebastian.huber at embedded-brains.de>  wrote:
>>>> On 27.04.23 02:11, Chris Johns wrote:
>>>>> On 26/4/2023 6:04 pm, Sebastian Huber wrote:
>>>>>> The CSafeLoader uses the C libyaml libary to considerably speed up the
>>>>>> loading of YAML files.
>>>>> No from me.
>>>> What do you mean with not for me? You have the CSafeLoader available and
>>>> it is slow? Do you have some timings before and after the patch set for
>>>> a "./waf configure" and "./waf build"? On my systems the configure needs
>>>> less than a second with the CSafeLoader and the waf build setup time is
>>>> less than 100ms.
>>>>
>>>>> I do not agree with conditional states of operation in the build system that
>>>>> depend on packages a host has installed. If speed is an important factor all
>>>>> users then I suggest you find a means to have it available automatically on the
>>>>> hosts we support (Linux, FreeBSD, MacOS, Windows MINGW64 and Cygwin.
>>>> I am not sure if we should automatically install system Python packages
>>>> on user machines.
>>>>
>>>> The fall back is the Python PyYAML package available through the RTEMS
>>>> sources. This is what we use currently. For RTEMS users, this is
>>>> acceptable since they are not supposed to touch the YAML files. For
>>>> RTEMS maintainers, not having the cache makes working with the build
>>>> system more efficient.
>>>>
>>>> If they system PyYAML package is not installed, then you get now a hint
>>>> to install it:
>>>>
>>>> Setting top to                           : /home/EB/sebastian_h/src/rtems
>>>> Setting out to                           :
>>>> /home/EB/sebastian_h/src/rtems/build
>>>> Regenerate the build specification cache.  Install the PyYAML Python
>>>> package to avoid this.  The cache regeneration needs a couple of seconds...
>>>> Configure board support package (BSP)    : arm/realview_pbx_a9_qemu
>>>>
>>> I have two questions, which are related to Chris's concern I think.
>>> 1. Are the output of PyYAML and C libyaml guaranteed to be consistent?
>>
>> I trust the PyYAML maintainers that the SafeLoader and CSafeLoader produce the
>> same results. With respect to the alternative ItemCache class implementation in
>> the wscript I am quite confident that this produces the same results. This part
>> just has to load the item data from the files. The CSafeLoader based ItemCache
>> has 53 lines of code.
>>
>>>
>>> 2. Why not make C libyaml part of the RTEMS toolchain?
>>>
>>> Any dependencies that exist in the build system are (by definition)
>>> suitable to be checked/provided by the tool buildset.
>>
>> Yes, this is an option. If we remove the pickle cache, then we force everyone to
>> use the libyaml based PyYAML module. Is this really necessary right now?
> 
> If we leave it who would do it? I would like to understand the next question
> before we decide if this is important. The key objective is to have consistent
> performance for every one. If the package is easy to build then we should do it
> when we build the tools and the questions we are having go away.

The PyYAML package had some security issues in the past. If we ship this 
package, who will monitor this package, update it, and write security 
advisories?

> 
>> For
>> most use cases the Python only solution works fine. If you spend your time
>> developing BSPs, then the CSafeLoader pays off.
> 
> Maybe I am not understanding how this works. Why is there a difference for
> developers vs a user who does not have this package installed? Does the
> difference scale?

A user typically just uses a certain version of RTEMS. Then the BSPs of 
interest are configured and built. A user is not supposed to touch the 
spec files.

A maintainer adds, modifies, removes spec files during development. With 
the item cache, this always involves a time to wait of several seconds. 
the time to wait depends on the total number of spec files. With the 
CSafeLoader this time is reduced to a fraction of a second.

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