[PATCH] riscv: entry: always initialize regs->a0 to -ENOSYS

[Björn Töpel]

Celeste Liu <coelacanthushex at gmail.com> writes:

> Otherwise when the tracer changes syscall number to -1, the kernel fails
> to initialize a0 with -ENOSYS and subsequently fails to return the error
> code of the failed syscall to userspace. For example, it will break
> strace syscall tampering.
>
> Fixes: 52449c17bdd1 ("riscv: entry: set a0 = -ENOSYS only when syscall != -1")
> Cc: stable at vger.kernel.org
> Signed-off-by: Celeste Liu <CoelacanthusHex at gmail.com>

Reported-by: "Dmitry V. Levin" <ldv at strace.io>
Reviewed-by: Björn Töpel <bjorn at rivosinc.com>