Fix default usage of reserved register

[appujee]

First, X27 X3 needs to be reserved. This is blocked on: https://reviews.llvm.org/D146463

• in llvm-project: X3 is already reserved by default and lld doesn't enable relax-gp by default.
• update bionic: https://android-review.git.corp.google.com/c/platform/bionic/+/2526531
• update ART: https://android-review.git.corp.google.com/c/platform/art/+/2535780

[enh-google]

not this one :-)

lib/hwasan/hwasan_setjmp_riscv64.S:  fsd   fs11, 25<<3(x10)

remember that we'll need to update bionic and ART if we make this change too.

(is libffi affected?)

[appujee]

not this one :-) lib/hwasan/hwasan_setjmp_riscv64.S: fsd fs11, 25<<3(x10)

striked it out.

(is libffi affected?)

doesn't seem like it: https://github.com/libffi/libffi/blob/master/src/riscv/sysv.S

[enh-google]

striked it out.

seems to have affected the wrong one?

[MaoHan001]

What is S11/X27 reserved for? I haven't seen any related topics. I previously only saw that the software SCS requires the use of S2/X18.

[appujee]

it is for the SCS. Previously S2 was reserved but it didn't appear to be a good choice. Some discussion is here: riscv-non-isa/riscv-elf-psabi-doc#370

[enh-google]

@appujee --- given that this bug is marked as blocking #78 do we actually need the kernel work here? that seems orthogonal?

[appujee]

makes sense. I've removed the item tracking kernel patches.