lib: sbi_emulate_csr: Do not log illegal CSR accesses

Illegal CSR accesses from lower privilege modes are delegated to S-mode
and do not necessarily indicate a bug. Supervisor software may want to
emulate some CSRs, or may intentionally disable access to certain
existing CSRs, and thus will expect traps when those CSRs are accessed.

For example, Linux disables sstatus.VS by default in order to detect
when userspace first accesses vector register state; this includes the
CSRs defined by the V extesion. As a result, if the first vector
instruction in a process is a CSR access, OpenSBI will log the illegal
instruction exception, even though there is no unexpected or erroneous
behavior occurring.

Since the illegal instruction exception is delegated to S-mode, S-mode
software should be responsible for reporting the exception, not OpenSBI.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

0 files changed, 0 insertions, 0 deletions