linux-user: Check type of microMIPS break instruction

microMIPS instructions that cause breakpoint exceptions come in
16-bit and 32-bit variants.  When handling exceptions caused by
such instructions, the instruction type needs to be taken into
account when extracting the break code.

The code has also been restructured for better clarity.

Signed-off-by: Kwok Cheung Yeung <kcy@codesourcery.com>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/main.c

@@ -2400,12 +2400,31 @@ done_syscall:
                 if (env->hflags & MIPS_HFLAG_M16) {
                     if (env->insn_flags & ASE_MICROMIPS) {
                         /* microMIPS mode */
-                        abi_ulong instr[2];
-
-                        ret = get_user_u16(instr[0], env->active_tc.PC) ||
-                              get_user_u16(instr[1], env->active_tc.PC + 2);
+                        ret = get_user_u16(trap_instr, env->active_tc.PC);
+                        if (ret != 0) {
+                            goto error;
+                        }
 
-                        trap_instr = (instr[0] << 16) | instr[1];
+                        if ((trap_instr >> 10) == 0x11) {
+                            /* 16-bit instruction */
+                            code = trap_instr & 0xf;
+                        } else {
+                            /* 32-bit instruction */
+                            abi_ulong instr_lo;
+
+                            ret = get_user_u16(instr_lo,
+                                               env->active_tc.PC + 2);
+                            if (ret != 0) {
+                                goto error;
+                            }
+                            trap_instr = (trap_instr << 16) | instr_lo;
+                            code = ((trap_instr >> 6) & ((1 << 20) - 1));
+                            /* Unfortunately, microMIPS also suffers from
+                               the old assembler bug...  */
+                            if (code >= (1 << 10)) {
+                                code >>= 10;
+                            }
+                        }
                     } else {
                         /* MIPS16e mode */
                         ret = get_user_u16(trap_instr, env->active_tc.PC);
@@ -2413,26 +2432,21 @@ done_syscall:
                             goto error;
                         }
                         code = (trap_instr >> 6) & 0x3f;
-                        if (do_break(env, &info, code) != 0) {
-                            goto error;
-                        }
-                        break;
                     }
                 } else {
                     ret = get_user_ual(trap_instr, env->active_tc.PC);
-                }
-
-                if (ret != 0) {
-                    goto error;
-                }
+                    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;
+                    /* 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) {