arch/mips/math-emu/dsemul.c

   1 #include <linux/compiler.h>
   2 #include <linux/mm.h>
   3 #include <linux/signal.h>
   4 #include <linux/smp.h>
   5
   6 #include <asm/asm.h>
   7 #include <asm/bootinfo.h>
   8 #include <asm/byteorder.h>
   9 #include <asm/cpu.h>
  10 #include <asm/inst.h>
  11 #include <asm/processor.h>
  12 #include <asm/uaccess.h>
  13 #include <asm/branch.h>
  14 #include <asm/mipsregs.h>
  15 #include <asm/system.h>
  16 #include <asm/cacheflush.h>
  17
  18 #include <asm/fpu_emulator.h>
  19
  20 #include "ieee754.h"
  21 #include "dsemul.h"
  22
  23 /* Strap kernel emulator for full MIPS IV emulation */
  24
  25 #ifdef __mips
  26 #undef __mips
  27 #endif
  28 #define __mips 4
  29
  30 /*
  31  * Emulate the arbritrary instruction ir at xcp->cp0_epc.  Required when
  32  * we have to emulate the instruction in a COP1 branch delay slot.  Do
  33  * not change cp0_epc due to the instruction
  34  *
  35  * According to the spec:
  36  * 1) it shouldnt be a branch :-)
  37  * 2) it can be a COP instruction :-(
  38  * 3) if we are tring to run a protected memory space we must take
  39  *    special care on memory access instructions :-(
  40  */
  41
  42 /*
  43  * "Trampoline" return routine to catch exception following
  44  *  execution of delay-slot instruction execution.
  45  */
  46
  47 struct emuframe {
  48         mips_instruction        emul;
  49         mips_instruction        badinst;
  50         mips_instruction        cookie;
  51         unsigned long           epc;
  52 };
  53
  54 int mips_dsemul(struct pt_regs *regs, mips_instruction ir, unsigned long cpc)
  55 {
  56         extern asmlinkage void handle_dsemulret(void);
  57         mips_instruction *dsemul_insns;
  58         struct emuframe *fr;
  59         int err;
  60
  61         if (ir == 0) {          /* a nop is easy */
  62                 regs->cp0_epc = cpc;
  63                 regs->cp0_cause &= ~CAUSEF_BD;
  64                 return 0;
  65         }
  66 #ifdef DSEMUL_TRACE
  67         printk("dsemul %lx %lx\n", regs->cp0_epc, cpc);
  68
  69 #endif
  70
  71         /*
  72          * The strategy is to push the instruction onto the user stack
  73          * and put a trap after it which we can catch and jump to
  74          * the required address any alternative apart from full
  75          * instruction emulation!!.
  76          *
  77          * Algorithmics used a system call instruction, and
  78          * borrowed that vector.  MIPS/Linux version is a bit
  79          * more heavyweight in the interests of portability and
  80          * multiprocessor support.  For Linux we generate a
  81          * an unaligned access and force an address error exception.
  82          *
  83          * For embedded systems (stand-alone) we prefer to use a
  84          * non-existing CP1 instruction. This prevents us from emulating
  85          * branches, but gives us a cleaner interface to the exception
  86          * handler (single entry point).
  87          */
  88
  89         /* Ensure that the two instructions are in the same cache line */
  90         dsemul_insns = (mips_instruction *) ((regs->regs[29] - sizeof(struct emuframe)) & ~0x7);
  91         fr = (struct emuframe *) dsemul_insns;
  92
  93         /* Verify that the stack pointer is not competely insane */
  94         if (unlikely(!access_ok(VERIFY_WRITE, fr, sizeof(struct emuframe))))
  95                 return SIGBUS;
  96
  97         err = __put_user(ir, &fr->emul);
  98         err |= __put_user((mips_instruction)BADINST, &fr->badinst);
  99         err |= __put_user((mips_instruction)BD_COOKIE, &fr->cookie);
 100         err |= __put_user(cpc, &fr->epc);
 101
 102         if (unlikely(err)) {
 103                 fpuemustats.errors++;
 104                 return SIGBUS;
 105         }
 106
 107         regs->cp0_epc = (unsigned long) &fr->emul;
 108
 109         flush_cache_sigtramp((unsigned long)&fr->badinst);
 110
 111         return SIGILL;          /* force out of emulation loop */
 112 }
 113
 114 int do_dsemulret(struct pt_regs *xcp)
 115 {
 116         struct emuframe *fr;
 117         unsigned long epc;
 118         u32 insn, cookie;
 119         int err = 0;
 120
 121         fr = (struct emuframe *) (xcp->cp0_epc - sizeof(mips_instruction));
 122
 123         /*
 124          * If we can't even access the area, something is very wrong, but we'll
 125          * leave that to the default handling
 126          */
 127         if (!access_ok(VERIFY_READ, fr, sizeof(struct emuframe)))
 128                 return 0;
 129
 130         /*
 131          * Do some sanity checking on the stackframe:
 132          *
 133          *  - Is the instruction pointed to by the EPC an BADINST?
 134          *  - Is the following memory word the BD_COOKIE?
 135          */
 136         err = __get_user(insn, &fr->badinst);
 137         err |= __get_user(cookie, &fr->cookie);
 138
 139         if (unlikely(err || (insn != BADINST) || (cookie != BD_COOKIE))) {
 140                 fpuemustats.errors++;
 141                 return 0;
 142         }
 143
 144         /*
 145          * At this point, we are satisfied that it's a BD emulation trap.  Yes,
 146          * a user might have deliberately put two malformed and useless
 147          * instructions in a row in his program, in which case he's in for a
 148          * nasty surprise - the next instruction will be treated as a
 149          * continuation address!  Alas, this seems to be the only way that we
 150          * can handle signals, recursion, and longjmps() in the context of
 151          * emulating the branch delay instruction.
 152          */
 153
 154 #ifdef DSEMUL_TRACE
 155         printk("dsemulret\n");
 156 #endif
 157         if (__get_user(epc, &fr->epc)) {                /* Saved EPC */
 158                 /* This is not a good situation to be in */
 159                 force_sig(SIGBUS, current);
 160
 161                 return 0;
 162         }
 163
 164         /* Set EPC to return to post-branch instruction */
 165         xcp->cp0_epc = epc;
 166
 167         return 1;
 168 }