arch/mips/kernel/branch.c

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Copyright (C) 1996, 97, 2000, 2001 by Ralf Baechle
   7  * Copyright (C) 2001 MIPS Technologies, Inc.
   8  */
   9 #include <linux/kernel.h>
  10 #include <linux/sched.h>
  11 #include <linux/signal.h>
  12 #include <asm/branch.h>
  13 #include <asm/cpu.h>
  14 #include <asm/cpu-features.h>
  15 #include <asm/fpu.h>
  16 #include <asm/inst.h>
  17 #include <asm/ptrace.h>
  18 #include <asm/uaccess.h>
  19
  20 /*
  21  * Compute the return address and do emulate branch simulation, if required.
  22  */
  23 int __compute_return_epc(struct pt_regs *regs)
  24 {
  25         unsigned int *addr, bit, fcr31, dspcontrol;
  26         long epc;
  27         union mips_instruction insn;
  28
  29         epc = regs->cp0_epc;
  30         if (epc & 3)
  31                 goto unaligned;
  32
  33         /*
  34          * Read the instruction
  35          */
  36         addr = (unsigned int *) epc;
  37         if (__get_user(insn.word, addr)) {
  38                 force_sig(SIGSEGV, current);
  39                 return -EFAULT;
  40         }
  41
  42         regs->regs[0] = 0;
  43         switch (insn.i_format.opcode) {
  44         /*
  45          * jr and jalr are in r_format format.
  46          */
  47         case spec_op:
  48                 switch (insn.r_format.func) {
  49                 case jalr_op:
  50                         regs->regs[insn.r_format.rd] = epc + 8;
  51                         /* Fall through */
  52                 case jr_op:
  53                         regs->cp0_epc = regs->regs[insn.r_format.rs];
  54                         break;
  55                 }
  56                 break;
  57
  58         /*
  59          * This group contains:
  60          * bltz_op, bgez_op, bltzl_op, bgezl_op,
  61          * bltzal_op, bgezal_op, bltzall_op, bgezall_op.
  62          */
  63         case bcond_op:
  64                 switch (insn.i_format.rt) {
  65                 case bltz_op:
  66                 case bltzl_op:
  67                         if ((long)regs->regs[insn.i_format.rs] < 0)
  68                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  69                         else
  70                                 epc += 8;
  71                         regs->cp0_epc = epc;
  72                         break;
  73
  74                 case bgez_op:
  75                 case bgezl_op:
  76                         if ((long)regs->regs[insn.i_format.rs] >= 0)
  77                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  78                         else
  79                                 epc += 8;
  80                         regs->cp0_epc = epc;
  81                         break;
  82
  83                 case bltzal_op:
  84                 case bltzall_op:
  85                         regs->regs[31] = epc + 8;
  86                         if ((long)regs->regs[insn.i_format.rs] < 0)
  87                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  88                         else
  89                                 epc += 8;
  90                         regs->cp0_epc = epc;
  91                         break;
  92
  93                 case bgezal_op:
  94                 case bgezall_op:
  95                         regs->regs[31] = epc + 8;
  96                         if ((long)regs->regs[insn.i_format.rs] >= 0)
  97                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  98                         else
  99                                 epc += 8;
 100                         regs->cp0_epc = epc;
 101                         break;
 102                 case bposge32_op:
 103                         if (!cpu_has_dsp)
 104                                 goto sigill;
 105
 106                         dspcontrol = rddsp(0x01);
 107
 108                         if (dspcontrol >= 32) {
 109                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
 110                         } else
 111                                 epc += 8;
 112                         regs->cp0_epc = epc;
 113                         break;
 114                 }
 115                 break;
 116
 117         /*
 118          * These are unconditional and in j_format.
 119          */
 120         case jal_op:
 121                 regs->regs[31] = regs->cp0_epc + 8;
 122         case j_op:
 123                 epc += 4;
 124                 epc >>= 28;
 125                 epc <<= 28;
 126                 epc |= (insn.j_format.target << 2);
 127                 regs->cp0_epc = epc;
 128                 break;
 129
 130         /*
 131          * These are conditional and in i_format.
 132          */
 133         case beq_op:
 134         case beql_op:
 135                 if (regs->regs[insn.i_format.rs] ==
 136                     regs->regs[insn.i_format.rt])
 137                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 138                 else
 139                         epc += 8;
 140                 regs->cp0_epc = epc;
 141                 break;
 142
 143         case bne_op:
 144         case bnel_op:
 145                 if (regs->regs[insn.i_format.rs] !=
 146                     regs->regs[insn.i_format.rt])
 147                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 148                 else
 149                         epc += 8;
 150                 regs->cp0_epc = epc;
 151                 break;
 152
 153         case blez_op: /* not really i_format */
 154         case blezl_op:
 155                 /* rt field assumed to be zero */
 156                 if ((long)regs->regs[insn.i_format.rs] <= 0)
 157                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 158                 else
 159                         epc += 8;
 160                 regs->cp0_epc = epc;
 161                 break;
 162
 163         case bgtz_op:
 164         case bgtzl_op:
 165                 /* rt field assumed to be zero */
 166                 if ((long)regs->regs[insn.i_format.rs] > 0)
 167                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 168                 else
 169                         epc += 8;
 170                 regs->cp0_epc = epc;
 171                 break;
 172
 173         /*
 174          * And now the FPA/cp1 branch instructions.
 175          */
 176         case cop1_op:
 177                 preempt_disable();
 178                 if (is_fpu_owner())
 179                         asm volatile("cfc1\t%0,$31" : "=r" (fcr31));
 180                 else
 181                         fcr31 = current->thread.fpu.fcr31;
 182                 preempt_enable();
 183
 184                 bit = (insn.i_format.rt >> 2);
 185                 bit += (bit != 0);
 186                 bit += 23;
 187                 switch (insn.i_format.rt & 3) {
 188                 case 0: /* bc1f */
 189                 case 2: /* bc1fl */
 190                         if (~fcr31 & (1 << bit))
 191                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
 192                         else
 193                                 epc += 8;
 194                         regs->cp0_epc = epc;
 195                         break;
 196
 197                 case 1: /* bc1t */
 198                 case 3: /* bc1tl */
 199                         if (fcr31 & (1 << bit))
 200                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
 201                         else
 202                                 epc += 8;
 203                         regs->cp0_epc = epc;
 204                         break;
 205                 }
 206                 break;
 207         }
 208
 209         return 0;
 210
 211 unaligned:
 212         printk("%s: unaligned epc - sending SIGBUS.\n", current->comm);
 213         force_sig(SIGBUS, current);
 214         return -EFAULT;
 215
 216 sigill:
 217         printk("%s: DSP branch but not DSP ASE - sending SIGBUS.\n", current->comm);
 218         force_sig(SIGBUS, current);
 219         return -EFAULT;
 220 }