arch/mips/math-emu/dsemul.c

   1 #include <asm/branch.h>
   2 #include <asm/cacheflush.h>
   3 #include <asm/fpu_emulator.h>
   4 #include <asm/inst.h>
   5 #include <asm/mipsregs.h>
   6 #include <asm/uaccess.h>
   7
   8 #include "ieee754.h"
   9
  10 /*
  11  * Emulate the arbitrary instruction ir at xcp->cp0_epc.  Required when
  12  * we have to emulate the instruction in a COP1 branch delay slot.  Do
  13  * not change cp0_epc due to the instruction
  14  *
  15  * According to the spec:
  16  * 1) it shouldn't be a branch :-)
  17  * 2) it can be a COP instruction :-(
  18  * 3) if we are tring to run a protected memory space we must take
  19  *    special care on memory access instructions :-(
  20  */
  21
  22 /*
  23  * "Trampoline" return routine to catch exception following
  24  *  execution of delay-slot instruction execution.
  25  */
  26
  27 struct emuframe {
  28         mips_instruction        emul;
  29         mips_instruction        badinst;
  30         mips_instruction        cookie;
  31         unsigned long           epc;
  32 };
  33
  34 /*
  35  * Set up an emulation frame for instruction IR, from a delay slot of
  36  * a branch jumping to CPC.  Return 0 if successful, -1 if no emulation
  37  * required, otherwise a signal number causing a frame setup failure.
  38  */
  39 int mips_dsemul(struct pt_regs *regs, mips_instruction ir, unsigned long cpc)
  40 {
  41         int isa16 = get_isa16_mode(regs->cp0_epc);
  42         mips_instruction break_math;
  43         struct emuframe __user *fr;
  44         int err;
  45
  46         /* NOP is easy */
  47         if (ir == 0)
  48                 return -1;
  49
  50         /* microMIPS instructions */
  51         if (isa16) {
  52                 union mips_instruction insn = { .word = ir };
  53
  54                 /* NOP16 aka MOVE16 $0, $0 */
  55                 if ((ir >> 16) == MM_NOP16)
  56                         return -1;
  57
  58                 /* ADDIUPC */
  59                 if (insn.mm_a_format.opcode == mm_addiupc_op) {
  60                         unsigned int rs;
  61                         s32 v;
  62
  63                         rs = (((insn.mm_a_format.rs + 0xe) & 0xf) + 2);
  64                         v = regs->cp0_epc & ~3;
  65                         v += insn.mm_a_format.simmediate << 2;
  66                         regs->regs[rs] = (long)v;
  67                         return -1;
  68                 }
  69         }
  70
  71         pr_debug("dsemul %lx %lx\n", regs->cp0_epc, cpc);
  72
  73         /*
  74          * The strategy is to push the instruction onto the user stack
  75          * and put a trap after it which we can catch and jump to
  76          * the required address any alternative apart from full
  77          * instruction emulation!!.
  78          *
  79          * Algorithmics used a system call instruction, and
  80          * borrowed that vector.  MIPS/Linux version is a bit
  81          * more heavyweight in the interests of portability and
  82          * multiprocessor support.  For Linux we use a BREAK 514
  83          * instruction causing a breakpoint exception.
  84          */
  85         break_math = BREAK_MATH(isa16);
  86
  87         /* Ensure that the two instructions are in the same cache line */
  88         fr = (struct emuframe __user *)
  89                 ((regs->regs[29] - sizeof(struct emuframe)) & ~0x7);
  90
  91         /* Verify that the stack pointer is not completely insane */
  92         if (unlikely(!access_ok(VERIFY_WRITE, fr, sizeof(struct emuframe))))
  93                 return SIGBUS;
  94
  95         if (isa16) {
  96                 err = __put_user(ir >> 16,
  97                                  (u16 __user *)(&fr->emul));
  98                 err |= __put_user(ir & 0xffff,
  99                                   (u16 __user *)((long)(&fr->emul) + 2));
 100                 err |= __put_user(break_math >> 16,
 101                                   (u16 __user *)(&fr->badinst));
 102                 err |= __put_user(break_math & 0xffff,
 103                                   (u16 __user *)((long)(&fr->badinst) + 2));
 104         } else {
 105                 err = __put_user(ir, &fr->emul);
 106                 err |= __put_user(break_math, &fr->badinst);
 107         }
 108
 109         err |= __put_user((mips_instruction)BD_COOKIE, &fr->cookie);
 110         err |= __put_user(cpc, &fr->epc);
 111
 112         if (unlikely(err)) {
 113                 MIPS_FPU_EMU_INC_STATS(errors);
 114                 return SIGBUS;
 115         }
 116
 117         regs->cp0_epc = (unsigned long)&fr->emul | isa16;
 118
 119         flush_cache_sigtramp((unsigned long)&fr->emul);
 120
 121         return 0;
 122 }
 123
 124 int do_dsemulret(struct pt_regs *xcp)
 125 {
 126         int isa16 = get_isa16_mode(xcp->cp0_epc);
 127         struct emuframe __user *fr;
 128         unsigned long epc;
 129         u32 insn, cookie;
 130         int err = 0;
 131         u16 instr[2];
 132
 133         fr = (struct emuframe __user *)
 134                 (msk_isa16_mode(xcp->cp0_epc) - sizeof(mips_instruction));
 135
 136         /*
 137          * If we can't even access the area, something is very wrong, but we'll
 138          * leave that to the default handling
 139          */
 140         if (!access_ok(VERIFY_READ, fr, sizeof(struct emuframe)))
 141                 return 0;
 142
 143         /*
 144          * Do some sanity checking on the stackframe:
 145          *
 146          *  - Is the instruction pointed to by the EPC an BREAK_MATH?
 147          *  - Is the following memory word the BD_COOKIE?
 148          */
 149         if (isa16) {
 150                 err = __get_user(instr[0],
 151                                  (u16 __user *)(&fr->badinst));
 152                 err |= __get_user(instr[1],
 153                                   (u16 __user *)((long)(&fr->badinst) + 2));
 154                 insn = (instr[0] << 16) | instr[1];
 155         } else {
 156                 err = __get_user(insn, &fr->badinst);
 157         }
 158         err |= __get_user(cookie, &fr->cookie);
 159
 160         if (unlikely(err ||
 161                      insn != BREAK_MATH(isa16) || cookie != BD_COOKIE)) {
 162                 MIPS_FPU_EMU_INC_STATS(errors);
 163                 return 0;
 164         }
 165
 166         /*
 167          * At this point, we are satisfied that it's a BD emulation trap.  Yes,
 168          * a user might have deliberately put two malformed and useless
 169          * instructions in a row in his program, in which case he's in for a
 170          * nasty surprise - the next instruction will be treated as a
 171          * continuation address!  Alas, this seems to be the only way that we
 172          * can handle signals, recursion, and longjmps() in the context of
 173          * emulating the branch delay instruction.
 174          */
 175
 176         pr_debug("dsemulret\n");
 177
 178         if (__get_user(epc, &fr->epc)) {                /* Saved EPC */
 179                 /* This is not a good situation to be in */
 180                 force_sig(SIGBUS, current);
 181
 182                 return 0;
 183         }
 184
 185         /* Set EPC to return to post-branch instruction */
 186         xcp->cp0_epc = epc;
 187         MIPS_FPU_EMU_INC_STATS(ds_emul);
 188         return 1;
 189 }