[PATCH] D70570: [PowerPC] Only use PLT annotations if using PIC relocation model

[Justin Hibbits via Phabricator via llvm-commits]

jhibbits added a comment.

@Bdragon28 we might need to use -mlongcall for modules, if we aren't already.  This should(?) force the compiler to generate the appropriate long-distance code sequences.  I'm not sure, though, if clang supports this yet.

@sfertile Thanks for reviewing this.  That ABI spec has been superseded generally by https://www.polyomino.org.uk/publications/2011/Power-Arch-32-bit-ABI-supp-1.0-Unified.pdf, which unifies that with the Linux ABI(s) and embedded ABI(s).  That also includes the secure-PLT reference.

Your overall understanding of the relocations involved and code generated is accurate.  To answer your questions:

- Newer linkers (GNU ld post-2.17.50) might be smart enough to convert to a local call.  However, GNU ld uses PLTREL relocations without the +0x8000 offset as an indicator of "BSS-PLT" in its heuristics.  This is what led to this change.
- It is an error to not use a PLTREL relocation for a call that needs to be indirected through the PLT.  The linker will complain to recompile with -fPIC.


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  https://reviews.llvm.org/D70570/new/

https://reviews.llvm.org/D70570