target-mips: Translate breaks and traps into the appropriate signal

GCC and GAS are capable of generating traps or breaks to check for
division by zero.  Additionally, GAS is capable of generating traps
or breaks to check for overflow on certain division and multiplication
operations.  The Linux kernel translates these traps and breaks into
signals.  This patch implements the corresponding feature in QEMU.
Signed-off-by: NMeador Inge <meadori@codesourcery.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

linux-user/main.c

@@ -2186,6 +2186,33 @@ static int do_store_exclusive(CPUMIPSState *env)
     return segv;
 }
 
+/* Break codes */
+enum {
+    BRK_OVERFLOW = 6,
+    BRK_DIVZERO = 7
+};
+
+static int do_break(CPUMIPSState *env, target_siginfo_t *info,
+                    unsigned int code)
+{
+    int ret = -1;
+
+    switch (code) {
+    case BRK_OVERFLOW:
+    case BRK_DIVZERO:
+        info->si_signo = TARGET_SIGFPE;
+        info->si_errno = 0;
+        info->si_code = (code == BRK_OVERFLOW) ? FPE_INTOVF : FPE_INTDIV;
+        queue_signal(env, info->si_signo, &*info);
+        ret = 0;
+        break;
+    default:
+        break;
+    }
+
+    return ret;
+}
+
 void cpu_loop(CPUMIPSState *env)
 {
     CPUState *cs = CPU(mips_env_get_cpu(env));
@@ -2302,8 +2329,55 @@ done_syscall:
             info.si_code = TARGET_ILL_ILLOPC;
             queue_signal(env, info.si_signo, &info);
             break;
+        /* The code below was inspired by the MIPS Linux kernel trap
+         * handling code in arch/mips/kernel/traps.c.
+         */
+        case EXCP_BREAK:
+            {
+                abi_ulong trap_instr;
+                unsigned int code;
+
+                ret = get_user_ual(trap_instr, env->active_tc.PC);
+                if (ret != 0) {
+                    goto error;
+                }
+
+                /* As described in the original Linux kernel code, the
+                 * below checks on 'code' are to work around an old
+                 * assembly bug.
+                 */
+                code = ((trap_instr >> 6) & ((1 << 20) - 1));
+                if (code >= (1 << 10)) {
+                    code >>= 10;
+                }
+
+                if (do_break(env, &info, code) != 0) {
+                    goto error;
+                }
+            }
+            break;
+        case EXCP_TRAP:
+            {
+                abi_ulong trap_instr;
+                unsigned int code = 0;
+
+                ret = get_user_ual(trap_instr, env->active_tc.PC);
+                if (ret != 0) {
+                    goto error;
+                }
+
+                /* The immediate versions don't provide a code.  */
+                if (!(trap_instr & 0xFC000000)) {
+                    code = ((trap_instr >> 6) & ((1 << 10) - 1));
+                }
+
+                if (do_break(env, &info, code) != 0) {
+                    goto error;
+                }
+            }
+            break;
         default:
-            //        error:
+error:
             fprintf(stderr, "qemu: unhandled CPU exception 0x%x - aborting\n",
                     trapnr);
             cpu_dump_state(env, stderr, fprintf, 0);