LXR linux/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 arbritrary 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
  27struct emuframe {
  28        mips_instruction        emul;
  29        mips_instruction        badinst;
  30        mips_instruction        cookie;
  31        unsigned long           epc;
  32};
  33
  34int mips_dsemul(struct pt_regs *regs, mips_instruction ir, unsigned long cpc)
  35{
  36        extern asmlinkage void handle_dsemulret(void);
  37        struct emuframe __user *fr;
  38        int err;
  39
  40        if ((get_isa16_mode(regs->cp0_epc) && ((ir >> 16) == MM_NOP16)) ||
  41                (ir == 0)) {
  42                /* NOP is easy */
  43                regs->cp0_epc = cpc;
  44                clear_delay_slot(regs);
  45                return 0;
  46        }
  47
  48        pr_debug("dsemul %lx %lx\n", regs->cp0_epc, cpc);
  49
  50        /*
  51         * The strategy is to push the instruction onto the user stack
  52         * and put a trap after it which we can catch and jump to
  53         * the required address any alternative apart from full
  54         * instruction emulation!!.
  55         *
  56         * Algorithmics used a system call instruction, and
  57         * borrowed that vector.  MIPS/Linux version is a bit
  58         * more heavyweight in the interests of portability and
  59         * multiprocessor support.  For Linux we generate a
  60         * an unaligned access and force an address error exception.
  61         *
  62         * For embedded systems (stand-alone) we prefer to use a
  63         * non-existing CP1 instruction. This prevents us from emulating
  64         * branches, but gives us a cleaner interface to the exception
  65         * handler (single entry point).
  66         */
  67
  68        /* Ensure that the two instructions are in the same cache line */
  69        fr = (struct emuframe __user *)
  70                ((regs->regs[29] - sizeof(struct emuframe)) & ~0x7);
  71
  72        /* Verify that the stack pointer is not competely insane */
  73        if (unlikely(!access_ok(VERIFY_WRITE, fr, sizeof(struct emuframe))))
  74                return SIGBUS;
  75
  76        if (get_isa16_mode(regs->cp0_epc)) {
  77                err = __put_user(ir >> 16, (u16 __user *)(&fr->emul));
  78                err |= __put_user(ir & 0xffff, (u16 __user *)((long)(&fr->emul) + 2));
  79                err |= __put_user(BREAK_MATH >> 16, (u16 __user *)(&fr->badinst));
  80                err |= __put_user(BREAK_MATH & 0xffff, (u16 __user *)((long)(&fr->badinst) + 2));
  81        } else {
  82                err = __put_user(ir, &fr->emul);
  83                err |= __put_user((mips_instruction)BREAK_MATH, &fr->badinst);
  84        }
  85
  86        err |= __put_user((mips_instruction)BD_COOKIE, &fr->cookie);
  87        err |= __put_user(cpc, &fr->epc);
  88
  89        if (unlikely(err)) {
  90                MIPS_FPU_EMU_INC_STATS(errors);
  91                return SIGBUS;
  92        }
  93
  94        regs->cp0_epc = ((unsigned long) &fr->emul) |
  95                get_isa16_mode(regs->cp0_epc);
  96
  97        flush_cache_sigtramp((unsigned long)&fr->badinst);
  98
  99        return SIGILL;          /* force out of emulation loop */
 100}
 101
 102int do_dsemulret(struct pt_regs *xcp)
 103{
 104        struct emuframe __user *fr;
 105        unsigned long epc;
 106        u32 insn, cookie;
 107        int err = 0;
 108        u16 instr[2];
 109
 110        fr = (struct emuframe __user *)
 111                (msk_isa16_mode(xcp->cp0_epc) - sizeof(mips_instruction));
 112
 113        /*
 114         * If we can't even access the area, something is very wrong, but we'll
 115         * leave that to the default handling
 116         */
 117        if (!access_ok(VERIFY_READ, fr, sizeof(struct emuframe)))
 118                return 0;
 119
 120        /*
 121         * Do some sanity checking on the stackframe:
 122         *
 123         *  - Is the instruction pointed to by the EPC an BREAK_MATH?
 124         *  - Is the following memory word the BD_COOKIE?
 125         */
 126        if (get_isa16_mode(xcp->cp0_epc)) {
 127                err = __get_user(instr[0], (u16 __user *)(&fr->badinst));
 128                err |= __get_user(instr[1], (u16 __user *)((long)(&fr->badinst) + 2));
 129                insn = (instr[0] << 16) | instr[1];
 130        } else {
 131                err = __get_user(insn, &fr->badinst);
 132        }
 133        err |= __get_user(cookie, &fr->cookie);
 134
 135        if (unlikely(err || (insn != BREAK_MATH) || (cookie != BD_COOKIE))) {
 136                MIPS_FPU_EMU_INC_STATS(errors);
 137                return 0;
 138        }
 139
 140        /*
 141         * At this point, we are satisfied that it's a BD emulation trap.  Yes,
 142         * a user might have deliberately put two malformed and useless
 143         * instructions in a row in his program, in which case he's in for a
 144         * nasty surprise - the next instruction will be treated as a
 145         * continuation address!  Alas, this seems to be the only way that we
 146         * can handle signals, recursion, and longjmps() in the context of
 147         * emulating the branch delay instruction.
 148         */
 149
 150        pr_debug("dsemulret\n");
 151
 152        if (__get_user(epc, &fr->epc)) {                /* Saved EPC */
 153                /* This is not a good situation to be in */
 154                force_sig(SIGBUS, current);
 155
 156                return 0;
 157        }
 158
 159        /* Set EPC to return to post-branch instruction */
 160        xcp->cp0_epc = epc;
 161
 162        return 1;
 163}
 164