cmd/link: rework .TOC. handling for ppc64le

Setup .TOC. to point to the same place for all objects. Today, the linker
assumes all call relocations can use the local function entry point of
imported object files. This requires a consistent pointer across all
objects.

This intentionally computes the .TOC. pointer in all linking configurations.
In some cases the .TOC. is not used today (e.g linking position-dependent go
only code). It is harmless and simple to compute in all cases, so just
do it for easier maintenance.

Notably, .TOC. is used in some cases when static linking is requested on
ppc64le/linux:

* Position-independent C code using a PC-rel relocation against .TOC.. cgo
  generated C object files are usually compiled PIC even if the go binary
  itself is not.

* Anything which causes PLT stub generation. The stubs always generate
  a .TOC. relative relocation.

* The race detector. Today, this links in an externally compiled archive which
  contains position-independent object files.

Similarly, position-independent linking is always punted to the external
linker on ppc64 today.

Updates #21961
Fixes #15409

Change-Id: Ifd8294b9249e16ba8b92eaf876d15d162f9c61fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/304458
Reviewed-by: Cherry Mui <cherryyz@google.com>
Trust: Lynn Boger <laboger@linux.vnet.ibm.com>

0 files changed, 0 insertions, 0 deletions