[PATCH 1/5] target/riscv: Ignore the S and U letters when formatting ISA strings

[Conor Dooley]

From: Palmer Dabbelt <palmer at sifive.com>

The ISA strings we're providing from QEMU aren't actually legal RISC-V
ISA strings, as both S and U cannot exist as single-letter extensions
and must instead be multi-letter strings.  We're still using the ISA
strings inside QEMU to track the availiable extensions, so just strip
out the S and U extensions when formatting ISA strings.

Signed-off-by: Palmer Dabbelt <palmer at sifive.com>
[Conor: rebased on 7.1.0-rc1 & slightly tweaked the commit message]
Signed-off-by: Conor Dooley <conor.dooley at microchip.com>
---
 target/riscv/cpu.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index ac6f82ebd0..95fdc03b3d 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -1122,7 +1122,23 @@ char *riscv_isa_string(RISCVCPU *cpu)
     char *p = isa_str + snprintf(isa_str, maxlen, "rv%d", TARGET_LONG_BITS);
     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]);
+            char lower = qemu_tolower(riscv_single_letter_exts[i]);
+            switch (lower) {
+                case 's':
+                case 'u':
+                    /*
+                    * The 's' and 'u' letters shouldn't show up in ISA strings as
+                    * they're not extensions, but they should show up in MISA.
+                    * Since we use these letters interally as a pseudo ISA string
+                    * to set MISA it's easier to just strip them out when
+                    * formatting the ISA string.
+                    */
+                    break;
+
+                default:
+                    *p++ = lower;
+                    break;
+            }
         }
     }
     *p = '\0';
-- 
2.37.1