[Bug target/108779] New: No option to change thread-pointer location on AArch64

[zach-gcc at cs dot stanford.edu via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108779

            Bug ID: 108779
           Summary: No option to change thread-pointer location on AArch64
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zach-gcc at cs dot stanford.edu
  Target Milestone: ---

On AArch64, GCC uses tpidr_el0 (user-mode accessible) to access the
thread-pointer for loading thread-local variables by default. There is no
option to change this to tpidr_el1 (or tpidr_el2/tpidr_el3), which is necessary
for using thread-local variables in kernel code (or any code that runs at a
higher privilege level). Clang has the `-mtp` option for AArch64
(https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-mtp)
that controls this, but it seems GCC does not. There is a GCC `-mtp` option for
ARM, but not AArch64.

See also the original gcc-help message I sent here:
https://gcc.gnu.org/pipermail/gcc-help/2023-February/142212.html

Thanks!