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 <linux/module.h>
  13 #include <asm/branch.h>
  14 #include <asm/cpu.h>
  15 #include <asm/cpu-features.h>
  16 #include <asm/fpu.h>
  17 #include <asm/inst.h>
  18 #include <asm/ptrace.h>
  19 #include <asm/uaccess.h>
  20
  21 /**
  22  * __compute_return_epc_for_insn - Computes the return address and do emulate
  23  *                                  branch simulation, if required.
  24  *
  25  * @regs:       Pointer to pt_regs
  26  * @insn:       branch instruction to decode
  27  * @returns:    -EFAULT on error and forces SIGBUS, and on success
  28  *              returns 0 or BRANCH_LIKELY_TAKEN as appropriate after
  29  *              evaluating the branch.
  30  */
  31 int __compute_return_epc_for_insn(struct pt_regs *regs,
  32                                    union mips_instruction insn)
  33 {
  34         unsigned int bit, fcr31, dspcontrol;
  35         long epc = regs->cp0_epc;
  36         int ret = 0;
  37
  38         switch (insn.i_format.opcode) {
  39         /*
  40          * jr and jalr are in r_format format.
  41          */
  42         case spec_op:
  43                 switch (insn.r_format.func) {
  44                 case jalr_op:
  45                         regs->regs[insn.r_format.rd] = epc + 8;
  46                         /* Fall through */
  47                 case jr_op:
  48                         regs->cp0_epc = regs->regs[insn.r_format.rs];
  49                         break;
  50                 }
  51                 break;
  52
  53         /*
  54          * This group contains:
  55          * bltz_op, bgez_op, bltzl_op, bgezl_op,
  56          * bltzal_op, bgezal_op, bltzall_op, bgezall_op.
  57          */
  58         case bcond_op:
  59                 switch (insn.i_format.rt) {
  60                 case bltz_op:
  61                 case bltzl_op:
  62                         if ((long)regs->regs[insn.i_format.rs] < 0) {
  63                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  64                                 if (insn.i_format.rt == bltzl_op)
  65                                         ret = BRANCH_LIKELY_TAKEN;
  66                         } else
  67                                 epc += 8;
  68                         regs->cp0_epc = epc;
  69                         break;
  70
  71                 case bgez_op:
  72                 case bgezl_op:
  73                         if ((long)regs->regs[insn.i_format.rs] >= 0) {
  74                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  75                                 if (insn.i_format.rt == bgezl_op)
  76                                         ret = BRANCH_LIKELY_TAKEN;
  77                         } else
  78                                 epc += 8;
  79                         regs->cp0_epc = epc;
  80                         break;
  81
  82                 case bltzal_op:
  83                 case bltzall_op:
  84                         regs->regs[31] = epc + 8;
  85                         if ((long)regs->regs[insn.i_format.rs] < 0) {
  86                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  87                                 if (insn.i_format.rt == bltzall_op)
  88                                         ret = BRANCH_LIKELY_TAKEN;
  89                         } else
  90                                 epc += 8;
  91                         regs->cp0_epc = epc;
  92                         break;
  93
  94                 case bgezal_op:
  95                 case bgezall_op:
  96                         regs->regs[31] = epc + 8;
  97                         if ((long)regs->regs[insn.i_format.rs] >= 0) {
  98                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
  99                                 if (insn.i_format.rt == bgezall_op)
 100                                         ret = BRANCH_LIKELY_TAKEN;
 101                         } else
 102                                 epc += 8;
 103                         regs->cp0_epc = epc;
 104                         break;
 105
 106                 case bposge32_op:
 107                         if (!cpu_has_dsp)
 108                                 goto sigill;
 109
 110                         dspcontrol = rddsp(0x01);
 111
 112                         if (dspcontrol >= 32) {
 113                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
 114                         } else
 115                                 epc += 8;
 116                         regs->cp0_epc = epc;
 117                         break;
 118                 }
 119                 break;
 120
 121         /*
 122          * These are unconditional and in j_format.
 123          */
 124         case jal_op:
 125                 regs->regs[31] = regs->cp0_epc + 8;
 126         case j_op:
 127                 epc += 4;
 128                 epc >>= 28;
 129                 epc <<= 28;
 130                 epc |= (insn.j_format.target << 2);
 131                 regs->cp0_epc = epc;
 132                 break;
 133
 134         /*
 135          * These are conditional and in i_format.
 136          */
 137         case beq_op:
 138         case beql_op:
 139                 if (regs->regs[insn.i_format.rs] ==
 140                     regs->regs[insn.i_format.rt]) {
 141                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 142                         if (insn.i_format.rt == beql_op)
 143                                 ret = BRANCH_LIKELY_TAKEN;
 144                 } else
 145                         epc += 8;
 146                 regs->cp0_epc = epc;
 147                 break;
 148
 149         case bne_op:
 150         case bnel_op:
 151                 if (regs->regs[insn.i_format.rs] !=
 152                     regs->regs[insn.i_format.rt]) {
 153                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 154                         if (insn.i_format.rt == bnel_op)
 155                                 ret = BRANCH_LIKELY_TAKEN;
 156                 } else
 157                         epc += 8;
 158                 regs->cp0_epc = epc;
 159                 break;
 160
 161         case blez_op: /* not really i_format */
 162         case blezl_op:
 163                 /* rt field assumed to be zero */
 164                 if ((long)regs->regs[insn.i_format.rs] <= 0) {
 165                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 166                         if (insn.i_format.rt == bnel_op)
 167                                 ret = BRANCH_LIKELY_TAKEN;
 168                 } else
 169                         epc += 8;
 170                 regs->cp0_epc = epc;
 171                 break;
 172
 173         case bgtz_op:
 174         case bgtzl_op:
 175                 /* rt field assumed to be zero */
 176                 if ((long)regs->regs[insn.i_format.rs] > 0) {
 177                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 178                         if (insn.i_format.rt == bnel_op)
 179                                 ret = BRANCH_LIKELY_TAKEN;
 180                 } else
 181                         epc += 8;
 182                 regs->cp0_epc = epc;
 183                 break;
 184
 185         /*
 186          * And now the FPA/cp1 branch instructions.
 187          */
 188         case cop1_op:
 189                 preempt_disable();
 190                 if (is_fpu_owner())
 191                         asm volatile("cfc1\t%0,$31" : "=r" (fcr31));
 192                 else
 193                         fcr31 = current->thread.fpu.fcr31;
 194                 preempt_enable();
 195
 196                 bit = (insn.i_format.rt >> 2);
 197                 bit += (bit != 0);
 198                 bit += 23;
 199                 switch (insn.i_format.rt & 3) {
 200                 case 0: /* bc1f */
 201                 case 2: /* bc1fl */
 202                         if (~fcr31 & (1 << bit)) {
 203                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
 204                                 if (insn.i_format.rt == 2)
 205                                         ret = BRANCH_LIKELY_TAKEN;
 206                         } else
 207                                 epc += 8;
 208                         regs->cp0_epc = epc;
 209                         break;
 210
 211                 case 1: /* bc1t */
 212                 case 3: /* bc1tl */
 213                         if (fcr31 & (1 << bit)) {
 214                                 epc = epc + 4 + (insn.i_format.simmediate << 2);
 215                                 if (insn.i_format.rt == 3)
 216                                         ret = BRANCH_LIKELY_TAKEN;
 217                         } else
 218                                 epc += 8;
 219                         regs->cp0_epc = epc;
 220                         break;
 221                 }
 222                 break;
 223 #ifdef CONFIG_CPU_CAVIUM_OCTEON
 224         case lwc2_op: /* This is bbit0 on Octeon */
 225                 if ((regs->regs[insn.i_format.rs] & (1ull<<insn.i_format.rt))
 226                      == 0)
 227                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 228                 else
 229                         epc += 8;
 230                 regs->cp0_epc = epc;
 231                 break;
 232         case ldc2_op: /* This is bbit032 on Octeon */
 233                 if ((regs->regs[insn.i_format.rs] &
 234                     (1ull<<(insn.i_format.rt+32))) == 0)
 235                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 236                 else
 237                         epc += 8;
 238                 regs->cp0_epc = epc;
 239                 break;
 240         case swc2_op: /* This is bbit1 on Octeon */
 241                 if (regs->regs[insn.i_format.rs] & (1ull<<insn.i_format.rt))
 242                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 243                 else
 244                         epc += 8;
 245                 regs->cp0_epc = epc;
 246                 break;
 247         case sdc2_op: /* This is bbit132 on Octeon */
 248                 if (regs->regs[insn.i_format.rs] &
 249                     (1ull<<(insn.i_format.rt+32)))
 250                         epc = epc + 4 + (insn.i_format.simmediate << 2);
 251                 else
 252                         epc += 8;
 253                 regs->cp0_epc = epc;
 254                 break;
 255 #endif
 256         }
 257
 258         return ret;
 259
 260 sigill:
 261         printk("%s: DSP branch but not DSP ASE - sending SIGBUS.\n", current->comm);
 262         force_sig(SIGBUS, current);
 263         return -EFAULT;
 264 }
 265 EXPORT_SYMBOL_GPL(__compute_return_epc_for_insn);
 266
 267 int __compute_return_epc(struct pt_regs *regs)
 268 {
 269         unsigned int __user *addr;
 270         long epc;
 271         union mips_instruction insn;
 272
 273         epc = regs->cp0_epc;
 274         if (epc & 3)
 275                 goto unaligned;
 276
 277         /*
 278          * Read the instruction
 279          */
 280         addr = (unsigned int __user *) epc;
 281         if (__get_user(insn.word, addr)) {
 282                 force_sig(SIGSEGV, current);
 283                 return -EFAULT;
 284         }
 285
 286         return __compute_return_epc_for_insn(regs, insn);
 287
 288 unaligned:
 289         printk("%s: unaligned epc - sending SIGBUS.\n", current->comm);
 290         force_sig(SIGBUS, current);
 291         return -EFAULT;
 292
 293 }