Add supervisor memory fence instruction SFENCE.VMA (sysprog21#458)

The supervisor memory-management fence instruction SFENCE.VMA is used
to synchronize updates to in-memory memory-management data structures
with current execution. Linux kernel leverage this instruction for
synchronization, support emulating this instruction is needed to boot
Linux kernel. Since we have only one hart and we have not yet support
cache (TLB) at present, the implementation of this instruction is
straight forward and it could be further improved in the future.

Related: sysprog21#310, sysprog21#438

src/decode.c

@@ -810,12 +810,22 @@ static inline bool op_system(rv_insn_t *ir, const uint32_t insn)
      * MRET   001100000010 00000 000    00000 1110011
      */
 
+    /* inst        funct7  rs2 rs1 funct3 rd     opcode
+     * -----------+-------+---+---+------+------+-------
+     * SFENCE.VMA  0001001 rs2 rs1  000   00000  1110011
+     */
+
     /* decode I-type */
     decode_itype(ir, insn);
 
     /* dispatch from funct3 field */
     switch (decode_funct3(insn)) {
     case 0:
+        if ((insn >> 25) == 0b0001001) { /* SFENCE.VMA */
+            ir->opcode = rv_insn_sfencevma;
+            break;
+        }
+
         /* dispatch from imm field */
         switch (ir->imm) {
         case 0: /* ECALL: Environment Call */

src/decode.h

@@ -80,6 +80,7 @@ enum op_field {
     _(sret, 1, 4, 0, ENC(rs1, rd))                     \
     _(hret, 0, 4, 0, ENC(rs1, rd))                     \
     _(mret, 1, 4, 0, ENC(rs1, rd))                     \
+    _(sfencevma, 1, 4, 0, ENC(rs1, rs2, rd))           \
     /* RV32 Zifencei Standard Extension */             \
     IIF(RV32_HAS(Zifencei))(                           \
         _(fencei, 1, 4, 0, ENC(rs1, rd))               \

src/rv32_constopt.c

@@ -374,9 +374,14 @@ CONSTOPT(sret, {})
 /* HRET: return from traps in H-mode */
 CONSTOPT(hret, {})
 
-/* MRET: return from traps in U-mode */
+/* MRET: return from traps in M-mode */
 CONSTOPT(mret, {})
 
+/* SFENCE.VMA: synchronize updates to in-memory memory-management data
+ * structures with current execution
+ */
+CONSTOPT(sfencevma, {})
+
 #if RV32_HAS(Zifencei) /* RV32 Zifencei Standard Extension */
 CONSTOPT(fencei, {})
 #endif

src/rv32_template.c

@@ -1019,6 +1019,20 @@ RVOP(
         assert; /* FIXME: Implement */
     }))
 
+/* SFENCE.VMA: synchronize updates to in-memory memory-management data
+ * structures with current execution
+ */
+RVOP(
+    sfencevma,
+    {
+        PC += 4;
+        /* FIXME: fill real implementations */
+        goto end_op;
+    },
+    GEN({
+        assert; /* FIXME: Implement */
+    }))
+
 #if RV32_HAS(Zifencei) /* RV32 Zifencei Standard Extension */
 RVOP(
     fencei,

src/t2c_template.c

@@ -305,6 +305,8 @@ T2C_OP(hret, { __UNREACHABLE; })
 
 T2C_OP(mret, { __UNREACHABLE; })
 
+T2C_OP(sfencevma, { __UNREACHABLE; })
+
 #if RV32_HAS(Zifencei)
 T2C_OP(fencei, { __UNREACHABLE; })
 #endif