GNU property saga
Michael Matz
matz@suse.de
Mon Mar 4 17:25:00 GMT 2019
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.
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