accel/tcg: Fix computing of is_write for MIPS

Detect all MIPS store instructions in cpu_signal_handler for all available
MIPS versions, and set is_write if encountering such store instructions.

This fixed the error while dealing with self-modified code for MIPS.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Kele Huang <kele.hwang@gmail.com>
Signed-off-by: Xu Zou <iwatchnima@gmail.com>
Message-Id: <20201002081420.10814-1-kele.hwang@gmail.com>
[rth: Use uintptr_t for pc to fix n32 build error.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/user-exec.c

@@ -702,16 +702,51 @@ int cpu_signal_handler(int host_signum, void *pinfo,
 
 #elif defined(__mips__)
 
+#if defined(__misp16) || defined(__mips_micromips)
+#error "Unsupported encoding"
+#endif
+
 int cpu_signal_handler(int host_signum, void *pinfo,
                        void *puc)
 {
     siginfo_t *info = pinfo;
     ucontext_t *uc = puc;
-    greg_t pc = uc->uc_mcontext.pc;
-    int is_write;
+    uintptr_t pc = uc->uc_mcontext.pc;
+    uint32_t insn = *(uint32_t *)pc;
+    int is_write = 0;
+
+    /* Detect all store instructions at program counter. */
+    switch((insn >> 26) & 077) {
+    case 050: /* SB */
+    case 051: /* SH */
+    case 052: /* SWL */
+    case 053: /* SW */
+    case 054: /* SDL */
+    case 055: /* SDR */
+    case 056: /* SWR */
+    case 070: /* SC */
+    case 071: /* SWC1 */
+    case 074: /* SCD */
+    case 075: /* SDC1 */
+    case 077: /* SD */
+#if !defined(__mips_isa_rev) || __mips_isa_rev < 6
+    case 072: /* SWC2 */
+    case 076: /* SDC2 */
+#endif
+        is_write = 1;
+        break;
+    case 023: /* COP1X */
+        /* Required in all versions of MIPS64 since
+           MIPS64r1 and subsequent versions of MIPS32r2. */
+        switch (insn & 077) {
+        case 010: /* SWXC1 */
+        case 011: /* SDXC1 */
+        case 015: /* SUXC1 */
+            is_write = 1;
+        }
+        break;
+    }
 
-    /* XXX: compute is_write */
-    is_write = 0;
     return handle_cpu_signal(pc, info, is_write, &uc->uc_sigmask);
 }