Make misa.C test conform to Hauser proposal

See https://github.com/riscv/riscv-isa-manual/commit/0472bcdd166f45712492829a250e228bb45fa5e7

diff --git a/isa/rv64si/ma_fetch.S b/isa/rv64si/ma_fetch.S
index a07d06daec99ece3ed24a06522d243a49cbce364..7d2adec9178582c0194f3c1a88506b77a36cd013 100644 (file)
--- a/isa/rv64si/ma_fetch.S
+++ b/isa/rv64si/ma_fetch.S
@@ -107,35 +107,27 @@ RVTEST_CODE_BEGIN
 2:
 
 #ifdef __MACHINE_MODE
-  # If RVC can be disabled, then disabling it should cause a misaligned
-  # instruction exception on the next instruction.  (This test assumes
-  # no other extensions that support misalignment are present.)
+  # RVC cannot be disabled if doing so would cause a misaligned instruction
+  # exception on the next instruction fetch. (This test assumes no other
+  # extensions that support misalignment are present.)
   li TESTNUM, 8
   csrr t2, misa
   andi t2, t2, 1 << ('c' - 'a')
   beqz t2, 2f
 
-  la t0, 1f
   .option rvc
   c.nop
   csrci misa, 1 << ('c' - 'a')
 1:
-  c.j 1f
+  c.nop
   .option norvc
 
-  # If we got here, we trapped.  Re-enable RVC and proceed.
-  csrsi misa, 1 << ('c' - 'a')
-  j 2f
-
-1:
-  # If we got here, we didn't trap, so RVC had better be enabled.
   csrr t2, misa
   andi t2, t2, 1 << ('c' - 'a')
   beqz t2, fail
 
-2:
-  # mret to a misaligned mepc should either align the mepc or raise a
-  # misaligned instruction exception.
+  # When RVC is disabled, mret to a misaligned mepc should succeed,
+  # masking off mepc[1].
   la t0, 1f
   addi t0, t0, -2
   csrw mepc, t0
@@ -150,33 +142,12 @@ RVTEST_CODE_BEGIN
   csrs mstatus, t2
   mret
 
-  # If the implementation chose to align mepc, mret will transfer control
-  # to this branch.  Otherwise, it will transfer control two bytes into
-  # the branch, which happens to be the illegal instruction c.unimp.
-  # But c.unimp should not be executed, since the PC is misaligned.
+  # mret should transfer control to this branch.  Otherwise, it will
+  # transfer control two bytes into the branch, which happens to be the
+  # illegal instruction c.unimp.
   beqz x0, 1f
 1:
-  j 2f
-
-test8_handler:
-  # verify trap cause
-  li a1, CAUSE_MISALIGNED_FETCH
-  csrr a0, mcause
-  bne a0, a1, fail
-
-  # check that mepc == t0, and advance mepc past the misalignment
-  csrr a0, mepc
-  bne a0, t0, fail
-  addi a0, a0, 2
-  csrw mepc, a0
-
-  # check that badaddr == t0 or zero
-  csrr a0, mbadaddr
-  beqz a0, 1f
-  bne a0, t0, fail
-1:
-  mret
-
+  csrsi misa, 1 << ('c' - 'a')
 2:
 #endif
 
@@ -196,10 +167,6 @@ stvec_handler:
   beq TESTNUM, a0, 1f
   li a0, 6
   beq TESTNUM, a0, 1f
-#ifdef __MACHINE_MODE
-  li a0, 8
-  beq TESTNUM, a0, test8_handler
-#endif
   j fail
 1: