[Bug Report]There is an error in the implementation of mepc[0]. #149

Description

Nutshell does not check whether mepc[0] is zero.
Described in the privileged specification 3.1.14:

The low bit of mepc (mepc[0]) is always zero.

Environment

Implementation: Nutshell
Test case: See attachment

Expected Behavior

When attempting to write a value to mepc, it is required that mepc[0] must be 0.

Observed Behavior

In Spike: when writing to mepc, the last bit is forcibly set to 0.
In Nutshell: It is not forcibly set to 0. This violates the specification.

Potential Impact

Not sure.

Result log display:

The assembly code context for 'mret' is as follows(Note:for more details, please refer to the attachment):

-                   la x14, 0 #To check
-                   addi x14,x14,1 #To check
-                   csrw 0x341, x14

mepc different at pc = 0x00800001a8, spike = 0x0000000000000000, Nutshell= 0x0000000000000001

I am looking forward to your insights and resolution on this matter. If I have any inaccuracies, please point them out. If you also consider this to be an issue, please let me know.

testcase.zip