GNU property saga

[Michael Matz <matz@suse.de>]

Hello,

I'll admit that I have lost track of the consensus about GNU properties 
and all the discussions last year.  But we want to somewhen get this into 
the psABI document.  I believe there were two points (with subitems) of 
contentions:

1) use PT_NOTE vs PT_xxx for program header containing the properties

I believe the consensus was to use a new PT_xxx value

1a) use new SHT_xxx for sections contain such properties

I believe the consensus was to stay with SHT_NOTE, even though that is
squarely against ELF spirit.

2) semantics of individual ranges of the GNU_PROPERTY_xxx value.

Basically the properties are split into three ranges, where each 
individual member represents itself a set of 32 members (via an uint32) 
representing a feature/property each.  The semantics of the higher level 
(the three ranges) are a fixed set of logical combinations of input 
values:
  * there is a range representing the AND of all input values
  * there is a range representing the OR of all input values
  * there is a range representing something strange (OR_AND), which tries
    to capture the notion of difference between "input-unknown" and 
    "input-known-not-there"

I believe there is consensus on the semantics of the AND and OR range.
Was there ever consensus on the OR_AND thingy?  It strikes me as not 
really implementing what is wanted, especially in relation to future 
extensibility (I'll write a mail about this).

Were there other points of contention, or was that all?

(FWIW, the current textual diff to the psABI document adding GNU 
properties is at 
https://gitlab.com/x86-psABIs/x86-64-ABI/merge_requests/1/diffs )


Ciao,
Michael.