target/riscv: add trace in riscv_raise_exception()

target/riscv: add trace in riscv_raise_exception()

When using system mode we can get the CPU traps being taken via the
'riscv_trap' trace or the "-d int" qemu log. User mode does not a way of
logging/showing exceptions to users.

Add a trace in riscv_raise_exception() to allow qemu-riscv(32/64) users
to check all exceptions being thrown. This is particularly useful to
help identifying insns that are throwing SIGILLs.

As it is today we need to debug their binaries to identify where the
illegal insns are:

$ ~/work/qemu/build/qemu-riscv64 -cpu rv64 ./foo.out
Illegal instruction (core dumped)

After this change users can capture the trace and use EPC to pinpoint
the insn:

$ ~/work/qemu/build/qemu-riscv64 -cpu rv64 -trace riscv_exception ./foo.out
riscv_exception 8 (user_ecall) on epc 0x17cd2
riscv_exception 8 (user_ecall) on epc 0x17cda
riscv_exception 8 (user_ecall) on epc 0x17622
(...)
riscv_exception 2 (illegal_instruction) on epc 0x1053a
Illegal instruction (core dumped)

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250106173734.412353-3-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>