[Scons-users] Make all Program and SharedLibrary targets implicitly Precious?

[Andrew C. Morrow]

Definitely a possibility. MongoDB probes for compiler support for ld.gold
and prefers it by default:

https://github.com/mongodb/mongo/blob/master/SConstruct#L2164-L2167

The downside to using incremental linking and making dynamic targets
Precious is that by overwriting the binaries you end up crashing running
programs that have them mapped. That happens often enough during developer
workflow that it is unfortunate.

So, it definitely should be opt-in behavior, and a Tool sounds right for
that.

I also wonder whether such a Tool might be able to make intelligent use of
gold's --incremental-base file to avoid the above problem. If you first
copied the dynamic target aside under a different name, then unlinked the
original, then used --incremental-base pointing to the moved-aside file,
perhaps you could avoid crashing programs that have the target mapped. I'm
not sure though if the cost of the file copy would eat up most of the gains
from incremental linking.

That sounds complex enough to also warrant a separate Tool.


On Fri, Apr 29, 2016 at 1:52 PM, Bill Deegan <bill at baddogconsulting.com>
wrote:

> Andrew,
>
> Might make sense to make a gold linker tool?
>
> -Bill
>
> On Fri, Apr 29, 2016 at 9:47 AM, Andrew C. Morrow <
> andrew.c.morrow at gmail.com> wrote:
>
>>
>> Thanks Bill -
>>
>> I think that sounds promising, I'll give it a look. If I get it working
>> well I'll ping the list back and describe my findings.
>>
>> Thanks,
>> Andrew
>>
>> On Fri, Apr 29, 2016 at 12:10 PM, Bill Deegan <bill at baddogconsulting.com>
>> wrote:
>>
>>> Andrew,
>>>
>>> Likely you want to stick this logic in the emitter for building
>>> libraries and programs.
>>> SCons/Tool/link.py  shlib_emitter() is the current logic.
>>> The environment tracks this in:
>>> env['SHLIBEMITTER'] which is a list.
>>> So if you append to SHLIBEMITTER and mark the relevant nodes Precious()
>>> env['PROGEMITTER'] is the emitter for programs. Looks like it's only
>>> defined for mslink and qt, so you can defined one on non qt/mslink freely
>>> and do the same.
>>>
>>> Hope that helps
>>> -Bill
>>>
>>>
>>> On Fri, Apr 29, 2016 at 8:52 AM, William Blevins <wblevins001 at gmail.com>
>>> wrote:
>>>
>>>> Andrew,
>>>>
>>>> I expect that you could make a Pseudo-Builder that wraps Program and
>>>> Library calls, and replace the top-level calls with your wrappers.
>>>>
>>>> I think you can replace them like env['BUILDERS']['xxxxxx'] = Wrapper
>>>> or env.AddMethod but I haven't tested this explicitly.
>>>>
>>>> https://bitbucket.org/scons/scons/wiki/ToolsForFools
>>>>
>>>> V/R,
>>>> William
>>>>
>>>> On Fri, Apr 29, 2016 at 4:21 PM, Andrew C. Morrow <
>>>> andrew.c.morrow at gmail.com> wrote:
>>>>
>>>>>
>>>>> Hi -
>>>>>
>>>>> Is there a simple way to do this? I'd like to use ld.gold's
>>>>> incremental linking, but I don't want to need to add .Precious to every
>>>>> executable and library in my project.
>>>>>
>>>>> Thanks,
>>>>> Andrew
>>>>>
>>>>>
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>>>>>
>>>>
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