Nathan,
Sorry for jumping in a relatively old thread. I saw this in mailing list
archives during a web search (I wasn't on this mailing list before). I
decided to speak up as I would be an affected party if this patch (or
some similar future patch) gets accepted or worse yet, the feature
involved gets disabled.
> Apparently there are legitimate reasons one might want the -mno-PDITR
behaviour without -mSPB. I don't know what those are, perhaps Joey could
clarify?
Yes, there are some practical use cases that require
-mno-pic-data-is-text-relative (-mno-PDITR) without -msingle-pic-base
(-mSPB).
These are based on two primary principles:
1. In the absence of lazy binding (that is almost always the case in
embedded systems), GOT is practically read-only - it needs to be
modified only during linking by the dynamic linker, after that it can be
considered and marked read-only (e.g. read-only attribute set to be
enforced by some MMU or MPU).
2. If you only need a simple dynamic object model - where you just need
dynamic loading and dynamic linking - but do not need to maintain
multiple data states for the object like you need in a traditional
shared object model, then one instance of GOT per dynamic object is enough.
From #1: GOT is read-only so keeping it with CODE segment is a natural
choice. Now as there is no need to move it to RAM so there is no need
for a mechanism (-mSPB) that would enable controlling the GOT location
independently of CODE segment.
From #2: Only one instance of GOT is required per dynamic object so
there is no need for a mechanism (-mSPB) that would enable switching GOTs.
So when both #1 and #2 are met, you only need
-mno-pic-data-is-text-relative.
Irfan Ahmad
