hw/riscv: boot: Don't use CSRs if they are disabled

If the CSRs and CSR instructions are disabled because the Zicsr
extension isn't enabled then we want to make sure we don't run any CSR
instructions in the boot ROM.

This patches removes the CSR instructions from the reset-vec if the
extension isn't enabled. We replace the instruction with a NOP instead.

Note that we don't do this for the SiFive U machine, as we are modelling
the hardware in that case.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1447
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230123035754.75553-1-alistair.francis@opensource.wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

diff --git a/hw/riscv/boot.c b/hw/riscv/boot.c
index 2594276223768c564fd37977b432a6219c27158f..cb27798a259a60ce2f249dee8bdb6dbdde4a3f43 100644 (file)
--- a/hw/riscv/boot.c
+++ b/hw/riscv/boot.c
@@ -356,6 +356,15 @@ void riscv_setup_rom_reset_vec(MachineState *machine, RISCVHartArrayState *harts
         reset_vec[4] = 0x0182b283;   /*     ld     t0, 24(t0) */
     }
 
+    if (!harts->harts[0].cfg.ext_icsr) {
+        /*
+         * The Zicsr extension has been disabled, so let's ensure we don't
+         * run the CSR instruction. Let's fill the address with a non
+         * compressed nop.
+         */
+        reset_vec[2] = 0x00000013;   /*     addi   x0, x0, 0 */
+    }
+
     /* copy in the reset vector in little_endian byte order */
     for (i = 0; i < ARRAY_SIZE(reset_vec); i++) {
         reset_vec[i] = cpu_to_le32(reset_vec[i]);