tree 1b90edc36c176df05522c0e1d3c979e25c71ca53
parent f937bad953c04638565cd20487623d19601e0c6b
author Elliott Hughes <enh@google.com> 1681334472 -0700
committer Elliott Hughes <enh@google.com> 1681334684 -0700

riscv64: stop reserving x18 for shadow call stack.

We're switching from x18 to gp, in stages. This change frees up x18
again now bionic and ART have switched to gp. There's no need for a
corresponding "reserve gp" change because gp is automatically reserved.
That's what makes it the perfect choice for shadow call stack (at
least until we get Zsslpcfi and an actual hardware shadow stack pointer
special-purpose register).

Bug: https://github.com/google/android-riscv64/issues/72
Bug: http://b/277909695
Test: treehugger
Change-Id: Iaee1d44cba8daf5d4a27a3791fe3cc28ed1a5d9a