checkasm/riscv: preserve T1 whilst calling...

This preserves T1 whilst calling the instrumented function. In a Sci-Fi
setting where type-based Control Flow Integrity (CFI) is supported, the
calling code (i.e., the `checkasm` test case) will set T1 to the expected
value of the landing pad label (LPL) of the instrumented function.

The call wrapper will always use LPL zero which is a wild card. We should
preserve the value of T1 at least until the indirect call to the
instrumented function. Of course this is Sci-Fi, because:
1) there is no hardware (or even QEMU) support yet,
2) all our assembler functions currently use LPL zero anyway.

This uses T3 rather than T2 because indirect branches with T2 is reserved
for notionally direct calls made with an indirect call instruction (e.g.
due to GOT indirection), and are exempted from forward-edge CFI checks.

0 files changed, 0 insertions, 0 deletions