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