[PATCH 01/10] build: Generate build hash

[Sebastian Huber]

On 25/02/2021 05:13, Chris Johns wrote:

> On 25/2/21 12:57 am, Sebastian Huber wrote:
>> Update #4265.
>> ---
>>   wscript | 27 ++++++++++++++++++++++++++-
>>   1 file changed, 26 insertions(+), 1 deletion(-)
>>
>> diff --git a/wscript b/wscript
>> index 6626fafb74..83c7c446bb 100755
>> --- a/wscript
>> +++ b/wscript
>> @@ -1359,6 +1359,30 @@ def get_compiler(conf, cp, variant):
>>       return value
>>   
>>   
>> +def _generate_build_hash(conf):
>> +    import hashlib
>> +    import base64
>> +
>> +    build_hash = ""
>> +    for key in sorted(conf.env):
>> +        build_hash = build_hash + key + str(conf.env[key])
> I am pleased to see the environment is being addressed but on some modern
> operating systems the environment has become a bit of a beast. This means
> comparable values will be near impossible if the whole environment is included
> in the build hash.
>
> Should we look to use a list that is contained? A list that effects the code on
> the target? In a purest sense a hash created from the CU pieces in all target
> libraries would be ideal however this is recursive.
This is a good idea. Maybe we should iterate over all start files and 
libraries generated by the build and then create a hash of all 
executable sections. Then we recompile one object with a command line 
define with the build hash and replace this object in librtemscpu.a.
>
> Any chance of a build label set in the config.ini? :)
You want something like a rtems_get_build_label() which returns the 
value of RTEMS_BUILD_LABEL set in a config.ini (or a default, e.g. 
"arch/bsp")?
>
>> +    for discard in [
>> +        conf.env.PREFIX,
>> +        conf.bldnode.make_node(conf.env.VARIANT).abspath(),
>> +        conf.path.abspath(),
>> +    ]:
>> +        build_hash = build_hash.replace(discard, "")
> I do not follow this piece of logic.
It removes prefix, source and build paths.
>
>> +    state = hashlib.sha256()
>> +    state.update(build_hash.encode("utf-8"))
> Why the `utf-8` encode and then decode later?
The hash update needs a byte stream not a string. The define needs a 
string and not a byte stream.
>
>> +    conf.define(
>> +        "RTEMS_BUILD_HASH",
>> +        base64.urlsafe_b64encode(state.digest()).decode("utf-8"),
> Thank you for base64 encoding the result.
>
> Chris

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