[PATCH] sectiongroup support

Nick Kledzik kledzik at apple.com
Mon Mar 17 16:43:17 PDT 2014

On Mar 17, 2014, at 4:34 PM, Shankar Easwaran <shankare at codeaurora.org> wrote:

> On 3/17/2014 6:24 PM, Nick Kledzik wrote:
>> On Mar 17, 2014, at 3:48 PM, Shankar Easwaran <shankare at codeaurora.org> wrote:
>>>> I think the solution:
>>>> 1) keep the existing canonical form for an atom graph that Passes process
>>>> 2) make the ELF Writer smart that when it writes relocatable object files, to synthesize undefined symbols for references into group children
>>>> 3) Have the YAML Reader be dumb and not synthesize any undefines.  Test cases for groups that want undefines will need to explicitly have them in the yaml.  This also enables you to write test cases that test the error case where an indirection though an undefine is not used.
>>> The below steps as in the command line would not work though.
>>> lld -flavor gnu -target x86_64 group.o --output-filetype=yaml --noinhibit-exec 
>>> (Input file is processed by the ELF reader, convert the read files to YAML files, re-read the files from YAML back into atoms)
>>> As the YAML reader wouldnt synthesize undefined atoms ? Its like a chicken-egg problem.
>> Think of the YAML Reader and Writer as dumb.  They just convert in-memory-objects <-> yaml.    Undefined are never synthesized (point 3 above).  If you want to write test cases for groups in yaml, you’ll need to explicitly add the UndefineAtom in the yaml file.  
> You are right that if the YAML reader and writer is used for testing, as well as the Native reader/writer. The problem will appear when the linker emittted YAML/Native file (after the resolver is complete) is used in a separate link, isnt it ?
> Is this a usecase that we would not be supporting ?

Basically, you told the linker to do its job and link together object files as if making a final executable, then use an option to the linker to save the atom graph as yaml or native.  Then try to use that atom graph later as if it is a input relocatable object.

The only use case I find interesting is once the native format settings down and someone wants to convert a file to it.  It would be good to have a way to do that.  If need be, we could write a Pass that re-inserts UndefinedAtoms for references to group owned atoms and get that pass to run just when doing that conversion.


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