cmd/link: enforce larger alignment on split ppc64 text sections

When laying out, we lazily increase the alignment for text sections
as symbols are found requiring more. This works if the start of
the virtual address (VA) for the section is greater than or equal
to the alignment required by any symbols placed in this section.

The minimum alignment of the section is only known after all
symbols are placed. The starting VA of this section is adjusted
upwards in ld.(*Link).address to meet the requested alignment.

This is a problem if the starting VA of the text section is not
already aligned. This can happen when the final symbol placed
into the previous section results in an insufficiently aligned
start VA of the next text section.

To workaround this, additional text sections are split, and both
the starting VA, and alignment of the section are aligned up to
match the known worst case alignment.

64B is chosen as the worst case alignment for all ppc64 targets,
as it will respect PCALIGN and eventually prefixed instructions
which will be introduced in the future.

Likewise, the xcoff size calculations need to be improved to
handle padding bytes when function symbols have been aligned.
This is done by tracking the largest valid VA offset encountered
when placing symbols.

Change-Id: Iefef09a1ee7c963fb8dfce2288a084a95cb77fca
Reviewed-on: https://go-review.googlesource.com/c/go/+/307431
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>

0 files changed, 0 insertions, 0 deletions