target/riscv: misa to ISA string conversion fix

Some bits in RISC-V `misa' CSR should not be reflected in the ISA
string.  For instance, `S' and `U' (represents existence of supervisor
and user mode, respectively) in `misa' CSR must not be copied since
neither `S' nor `U' are valid single-letter extensions.

This commit also removes all reserved/dropped single-letter "extensions"
from the list.

-   "B": Not going to be a single-letter extension (misa.B is reserved).
-   "J": Not going to be a single-letter extension (misa.J is reserved).
-   "K": Not going to be a single-letter extension (misa.K is reserved).
-   "L": Dropped.
-   "N": Dropped.
-   "T": Dropped.

It also clarifies that the variable `riscv_single_letter_exts' is a
single-letter extension order list.

Signed-off-by: Tsukasa OI <research_trasio@irq.a4lg.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <4a4c11213a161a7eedabe46abe58b351bb0e2ef2.1648473008.git.research_trasio@irq.a4lg.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index cfdfe78..edc33c4 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -34,7 +34,7 @@
 
 /* RISC-V CPU definitions */
 
-static const char riscv_exts[26] = "IEMAFDQCLBJTPVNSUHKORWXYZG";
+static const char riscv_single_letter_exts[] = "IEMAFDQCPVH";
 
 const char * const riscv_int_regnames[] = {
   "x0/zero", "x1/ra",  "x2/sp",  "x3/gp",  "x4/tp",  "x5/t0",   "x6/t1",
@@ -911,12 +911,12 @@ static void riscv_cpu_class_init(ObjectClass *c, void *data)
 char *riscv_isa_string(RISCVCPU *cpu)
 {
     int i;
-    const size_t maxlen = sizeof("rv128") + sizeof(riscv_exts) + 1;
+    const size_t maxlen = sizeof("rv128") + sizeof(riscv_single_letter_exts);
     char *isa_str = g_new(char, maxlen);
     char *p = isa_str + snprintf(isa_str, maxlen, "rv%d", TARGET_LONG_BITS);
-    for (i = 0; i < sizeof(riscv_exts); i++) {
-        if (cpu->env.misa_ext & RV(riscv_exts[i])) {
-            *p++ = qemu_tolower(riscv_exts[i]);
+    for (i = 0; i < sizeof(riscv_single_letter_exts) - 1; i++) {
+        if (cpu->env.misa_ext & RV(riscv_single_letter_exts[i])) {
+            *p++ = qemu_tolower(riscv_single_letter_exts[i]);
         }
     }
     *p = '\0';