riscv: entry: Save a0 prior syscall_enter_from_user_mode()

The RISC-V calling convention passes the first argument, and the
return value in the a0 register. For this reason, the a0 register
needs some extra care; When handling syscalls, the a0 register is
saved into regs->orig_a0, so a0 can be properly restored for,
e.g. interrupted syscalls.

This functionality was broken with the introduction of the generic
entry patches. Here, a0 was saved into orig_a0 after calling
syscall_enter_from_user_mode(), which can change regs->a0 for some
paths, incorrectly restoring a0.

This is resolved, by saving a0 prior doing the
syscall_enter_from_user_mode() call.

Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reviewed-by: Heiko Stuebner <[email protected]>
Tested-by: Heiko Stuebner <[email protected]>
Signed-off-by: Björn Töpel <[email protected]>
Reported-by: Conor Dooley <[email protected]>
Reviewed-by: Conor Dooley <[email protected]>
Tested-by: Conor Dooley <[email protected]>
Tested-by: Geert Uytterhoeven <[email protected]>
Tested-by: Andy Chiu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

0 files changed, 0 insertions, 0 deletions