target/riscv: Fix ssamoswap error handling

Follow the RISC-V CFI v1.0 spec [1] to fix the exception type
when ssamoswap is disabled by xSSE.

[1] RISC-V CFI spec v1.0, ch2.7 Atomic Swap from a Shadow Stack Location

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250924074818.230010-4-jim.shu@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 49 insertions, 0 deletions

diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index 110292e84d..8382aa94cb 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -717,4 +717,53 @@ target_ulong helper_hyp_hlvx_wu(CPURISCVState *env, target_ulong addr)
     return cpu_ldl_code_mmu(env, addr, oi, ra);
 }
 
+void helper_ssamoswap_disabled(CPURISCVState *env)
+{
+    int exception = RISCV_EXCP_ILLEGAL_INST;
+
+    /*
+     * Here we follow the RISC-V CFI spec [1] to implement the exception type
+     * of ssamoswap* instruction.
+     *
+     * [1] RISC-V CFI spec v1.0, ch2.7 Atomic Swap from a Shadow Stack Location
+     *
+     * Note: We have already checked some conditions in trans_* functions:
+     *   1. The effective priv mode is not M-mode.
+     *   2. The xSSE specific to the effictive priv mode is disabled.
+     */
+    if (!get_field(env->menvcfg, MENVCFG_SSE)) {
+        /*
+         * Disabled M-mode SSE always trigger illegal instruction when
+         * current priv mode is not M-mode.
+         */
+        exception = RISCV_EXCP_ILLEGAL_INST;
+        goto done;
+    }
+
+    if (!riscv_has_ext(env, RVS)) {
+        /* S-mode is not implemented */
+        exception = RISCV_EXCP_ILLEGAL_INST;
+        goto done;
+    } else if (env->virt_enabled) {
+        /*
+         * VU/VS-mode with disabled xSSE will trigger the virtual instruction
+         * exception.
+         */
+        exception = RISCV_EXCP_VIRT_INSTRUCTION_FAULT;
+        goto done;
+    } else {
+        /*
+         * U-mode with disabled S-mode SSE will trigger the illegal instruction
+         * exception.
+         *
+         * Note: S-mode is already handled in the disabled M-mode SSE case.
+         */
+        exception = RISCV_EXCP_ILLEGAL_INST;
+        goto done;
+    }
+
+done:
+    riscv_raise_exception(env, exception, GETPC());
+}
+
 #endif /* !CONFIG_USER_ONLY */