src/soc/decoder/isa/caller.py

   1 """core of the python-based POWER9 simulator
   2
   3 this is part of a cycle-accurate POWER9 simulator.  its primary purpose is
   4 not speed, it is for both learning and educational purposes, as well as
   5 a method of verifying the HDL.
   6 """
   7
   8 from functools import wraps
   9 from soc.decoder.orderedset import OrderedSet
  10 from soc.decoder.selectable_int import (FieldSelectableInt, SelectableInt,
  11                                         selectconcat)
  12 from soc.decoder.power_enums import (spr_dict, spr_byname, XER_bits,
  13                                      insns, InternalOp)
  14 from soc.decoder.helpers import exts, trunc_div, trunc_rem
  15 from collections import namedtuple
  16 import math
  17 import sys
  18
  19 instruction_info = namedtuple('instruction_info',
  20                               'func read_regs uninit_regs write_regs ' + \
  21                               'special_regs op_fields form asmregs')
  22
  23 special_sprs = {
  24     'LR': 8,
  25     'CTR': 9,
  26     'TAR': 815,
  27     'XER': 1,
  28     'VRSAVE': 256}
  29
  30
  31 def swap_order(x, nbytes):
  32     x = x.to_bytes(nbytes, byteorder='little')
  33     x = int.from_bytes(x, byteorder='big', signed=False)
  34     return x
  35
  36
  37 def create_args(reglist, extra=None):
  38     args = OrderedSet()
  39     for reg in reglist:
  40         args.add(reg)
  41     args = list(args)
  42     if extra:
  43         args = [extra] + args
  44     return args
  45
  46
  47 class Mem:
  48
  49     def __init__(self, row_bytes=8, initial_mem=None):
  50         self.mem = {}
  51         self.bytes_per_word = row_bytes
  52         self.word_log2 = math.ceil(math.log2(row_bytes))
  53         print ("Sim-Mem", initial_mem, self.bytes_per_word, self.word_log2)
  54         if not initial_mem:
  55             return
  56
  57         # different types of memory data structures recognised (for convenience)
  58         if isinstance(initial_mem, list):
  59             initial_mem = (0, initial_mem)
  60         if isinstance(initial_mem, tuple):
  61             startaddr, mem = initial_mem
  62             initial_mem = {}
  63             for i, val in enumerate(mem):
  64                 initial_mem[startaddr + row_bytes*i] = (val, row_bytes)
  65
  66         for addr, (val, width) in initial_mem.items():
  67             #val = swap_order(val, width)
  68             self.st(addr, val, width, swap=False)
  69
  70     def _get_shifter_mask(self, wid, remainder):
  71         shifter = ((self.bytes_per_word - wid) - remainder) * \
  72             8  # bits per byte
  73         # XXX https://bugs.libre-soc.org/show_bug.cgi?id=377
  74         # BE/LE mode?
  75         shifter = remainder * 8
  76         mask = (1 << (wid * 8)) - 1
  77         print ("width,rem,shift,mask", wid, remainder, hex(shifter), hex(mask))
  78         return shifter, mask
  79
  80     # TODO: Implement ld/st of lesser width
  81     def ld(self, address, width=8, swap=True, check_in_mem=False):
  82         print("ld from addr 0x{:x} width {:d}".format(address, width))
  83         remainder = address & (self.bytes_per_word - 1)
  84         address = address >> self.word_log2
  85         assert remainder & (width - 1) == 0, "Unaligned access unsupported!"
  86         if address in self.mem:
  87             val = self.mem[address]
  88         elif check_in_mem:
  89             return None
  90         else:
  91             val = 0
  92         print("mem @ 0x{:x} rem {:d} : 0x{:x}".format(address, remainder, val))
  93
  94         if width != self.bytes_per_word:
  95             shifter, mask = self._get_shifter_mask(width, remainder)
  96             print ("masking", hex(val), hex(mask<<shifter), shifter)
  97             val = val & (mask << shifter)
  98             val >>= shifter
  99         if swap:
 100             val = swap_order(val, width)
 101         print("Read 0x{:x} from addr 0x{:x}".format(val, address))
 102         return val
 103
 104     def st(self, addr, v, width=8, swap=True):
 105         staddr = addr
 106         remainder = addr & (self.bytes_per_word - 1)
 107         addr = addr >> self.word_log2
 108         print("Writing 0x{:x} to ST 0x{:x} memaddr 0x{:x}/{:x}".format(v,
 109                         staddr, addr, remainder, swap))
 110         assert remainder & (width - 1) == 0, "Unaligned access unsupported!"
 111         if swap:
 112             v = swap_order(v, width)
 113         if width != self.bytes_per_word:
 114             if addr in self.mem:
 115                 val = self.mem[addr]
 116             else:
 117                 val = 0
 118             shifter, mask = self._get_shifter_mask(width, remainder)
 119             val &= ~(mask << shifter)
 120             val |= v << shifter
 121             self.mem[addr] = val
 122         else:
 123             self.mem[addr] = v
 124         print("mem @ 0x{:x}: 0x{:x}".format(addr, self.mem[addr]))
 125
 126     def __call__(self, addr, sz):
 127         val = self.ld(addr.value, sz)
 128         print ("memread", addr, sz, val)
 129         return SelectableInt(val, sz*8)
 130
 131     def memassign(self, addr, sz, val):
 132         print ("memassign", addr, sz, val)
 133         self.st(addr.value, val.value, sz)
 134
 135
 136 class GPR(dict):
 137     def __init__(self, decoder, regfile):
 138         dict.__init__(self)
 139         self.sd = decoder
 140         for i in range(32):
 141             self[i] = SelectableInt(regfile[i], 64)
 142
 143     def __call__(self, ridx):
 144         return self[ridx]
 145
 146     def set_form(self, form):
 147         self.form = form
 148
 149     def getz(self, rnum):
 150         #rnum = rnum.value # only SelectableInt allowed
 151         print("GPR getzero", rnum)
 152         if rnum == 0:
 153             return SelectableInt(0, 64)
 154         return self[rnum]
 155
 156     def _get_regnum(self, attr):
 157         getform = self.sd.sigforms[self.form]
 158         rnum = getattr(getform, attr)
 159         return rnum
 160
 161     def ___getitem__(self, attr):
 162         print("GPR getitem", attr)
 163         rnum = self._get_regnum(attr)
 164         return self.regfile[rnum]
 165
 166     def dump(self):
 167         for i in range(0, len(self), 8):
 168             s = []
 169             for j in range(8):
 170                 s.append("%08x" % self[i+j].value)
 171             s = ' '.join(s)
 172             print("reg", "%2d" % i, s)
 173
 174 class PC:
 175     def __init__(self, pc_init=0):
 176         self.CIA = SelectableInt(pc_init, 64)
 177         self.NIA = self.CIA + SelectableInt(4, 64)
 178
 179     def update(self, namespace):
 180         self.CIA = namespace['NIA'].narrow(64)
 181         self.NIA = self.CIA + SelectableInt(4, 64)
 182         namespace['CIA'] = self.CIA
 183         namespace['NIA'] = self.NIA
 184
 185
 186 class SPR(dict):
 187     def __init__(self, dec2, initial_sprs={}):
 188         self.sd = dec2
 189         dict.__init__(self)
 190         for key, v in initial_sprs.items():
 191             if isinstance(key, SelectableInt):
 192                 key = key.value
 193             key = special_sprs.get(key, key)
 194             if isinstance(key, int):
 195                 info = spr_dict[key]
 196             else:
 197                 info = spr_byname[key]
 198             if not isinstance(v, SelectableInt):
 199                 v = SelectableInt(v, info.length)
 200             self[key] = v
 201
 202     def __getitem__(self, key):
 203         print ("get spr", key)
 204         print ("dict", self.items())
 205         # if key in special_sprs get the special spr, otherwise return key
 206         if isinstance(key, SelectableInt):
 207             key = key.value
 208         if isinstance(key, int):
 209             key = spr_dict[key].SPR
 210         key = special_sprs.get(key, key)
 211         if key in self:
 212             res = dict.__getitem__(self, key)
 213         else:
 214             if isinstance(key, int):
 215                 info = spr_dict[key]
 216             else:
 217                 info = spr_byname[key]
 218             dict.__setitem__(self, key, SelectableInt(0, info.length))
 219             res = dict.__getitem__(self, key)
 220         print ("spr returning", key, res)
 221         return res
 222
 223     def __setitem__(self, key, value):
 224         if isinstance(key, SelectableInt):
 225             key = key.value
 226         if isinstance(key, int):
 227             key = spr_dict[key].SPR
 228             print ("spr key", key)
 229         key = special_sprs.get(key, key)
 230         print ("setting spr", key, value)
 231         dict.__setitem__(self, key, value)
 232
 233     def __call__(self, ridx):
 234         return self[ridx]
 235
 236
 237 class ISACaller:
 238     # decoder2 - an instance of power_decoder2
 239     # regfile - a list of initial values for the registers
 240     # initial_{etc} - initial values for SPRs, Condition Register, Mem, MSR
 241     # respect_pc - tracks the program counter.  requires initial_insns
 242     def __init__(self, decoder2, regfile, initial_sprs=None, initial_cr=0,
 243                        initial_mem=None, initial_msr=0,
 244                        initial_insns=None, respect_pc=False,
 245                        disassembly=None):
 246
 247         self.respect_pc = respect_pc
 248         if initial_sprs is None:
 249             initial_sprs = {}
 250         if initial_mem is None:
 251             initial_mem = {}
 252         if initial_insns is None:
 253             initial_insns = {}
 254             assert self.respect_pc == False, "instructions required to honor pc"
 255
 256         print ("ISACaller insns", respect_pc, initial_insns, disassembly)
 257
 258         # "fake program counter" mode (for unit testing)
 259         self.fake_pc = 0
 260         if not respect_pc:
 261             if isinstance(initial_mem, tuple):
 262                 self.fake_pc = initial_mem[0]
 263
 264         # disassembly: we need this for now (not given from the decoder)
 265         self.disassembly = {}
 266         if disassembly:
 267             for i, code in enumerate(disassembly):
 268                 self.disassembly[i*4 + self.fake_pc] = code
 269
 270         # set up registers, instruction memory, data memory, PC, SPRs, MSR
 271         self.gpr = GPR(decoder2, regfile)
 272         self.mem = Mem(row_bytes=8, initial_mem=initial_mem)
 273         self.imem = Mem(row_bytes=4, initial_mem=initial_insns)
 274         self.pc = PC()
 275         self.spr = SPR(decoder2, initial_sprs)
 276         self.msr = SelectableInt(initial_msr, 64) # underlying reg
 277
 278         # TODO, needed here:
 279         # FPR (same as GPR except for FP nums)
 280         # 4.2.2 p124 FPSCR (definitely "separate" - not in SPR)
 281         #            note that mffs, mcrfs, mtfsf "manage" this FPSCR
 282         # 2.3.1 CR (and sub-fields CR0..CR6 - CR0 SO comes from XER.SO)
 283         #         note that mfocrf, mfcr, mtcr, mtocrf, mcrxrx "manage" CRs
 284         #         -- Done
 285         # 2.3.2 LR   (actually SPR #8) -- Done
 286         # 2.3.3 CTR  (actually SPR #9) -- Done
 287         # 2.3.4 TAR  (actually SPR #815)
 288         # 3.2.2 p45 XER  (actually SPR #1) -- Done
 289         # 3.2.3 p46 p232 VRSAVE (actually SPR #256)
 290
 291         # create CR then allow portions of it to be "selectable" (below)
 292         self._cr = SelectableInt(initial_cr, 64) # underlying reg
 293         self.cr = FieldSelectableInt(self._cr, list(range(32,64)))
 294
 295         # "undefined", just set to variable-bit-width int (use exts "max")
 296         self.undefined = SelectableInt(0, 256) # TODO, not hard-code 256!
 297
 298         self.namespace = {}
 299         self.namespace.update(self.spr)
 300         self.namespace.update({'GPR': self.gpr,
 301                           'MEM': self.mem,
 302                           'SPR': self.spr,
 303                           'memassign': self.memassign,
 304                           'NIA': self.pc.NIA,
 305                           'CIA': self.pc.CIA,
 306                           'CR': self.cr,
 307                           'MSR': self.msr,
 308                           'undefined': self.undefined,
 309                           'mode_is_64bit': True,
 310                           'SO': XER_bits['SO']
 311                           })
 312
 313
 314         # field-selectable versions of Condition Register TODO check bitranges?
 315         self.crl = []
 316         for i in range(8):
 317             bits = tuple(range(i*4, (i+1)*4))# errr... maybe?
 318             _cr = FieldSelectableInt(self.cr, bits)
 319             self.crl.append(_cr)
 320             self.namespace["CR%d" % i] = _cr
 321
 322         self.decoder = decoder2.dec
 323         self.dec2 = decoder2
 324
 325     def TRAP(self, trap_addr=0x700):
 326         print ("TRAP: TODO")
 327         #self.namespace['NIA'] = trap_addr
 328         #self.SRR0 = self.namespace['CIA'] + 4
 329         #self.SRR1 = self.namespace['MSR']
 330         #self.namespace['MSR'][45] = 1
 331         # store CIA(+4?) in SRR0, set NIA to 0x700
 332         # store MSR in SRR1, set MSR to um errr something, have to check spec
 333
 334     def memassign(self, ea, sz, val):
 335         self.mem.memassign(ea, sz, val)
 336
 337     def prep_namespace(self, formname, op_fields):
 338         # TODO: get field names from form in decoder*1* (not decoder2)
 339         # decoder2 is hand-created, and decoder1.sigform is auto-generated
 340         # from spec
 341         # then "yield" fields only from op_fields rather than hard-coded
 342         # list, here.
 343         fields = self.decoder.sigforms[formname]
 344         for name in op_fields:
 345             if name == 'spr':
 346                 sig = getattr(fields, name.upper())
 347             else:
 348                 sig = getattr(fields, name)
 349             val = yield sig
 350             if name in ['BF', 'BFA']:
 351                 self.namespace[name] = val
 352             else:
 353                 self.namespace[name] = SelectableInt(val, sig.width)
 354
 355         self.namespace['XER'] = self.spr['XER']
 356         self.namespace['CA'] = self.spr['XER'][XER_bits['CA']].value
 357         self.namespace['CA32'] = self.spr['XER'][XER_bits['CA32']].value
 358
 359     def handle_carry_(self, inputs, outputs, already_done):
 360         inv_a = yield self.dec2.e.invert_a
 361         if inv_a:
 362             inputs[0] = ~inputs[0]
 363
 364         imm_ok = yield self.dec2.e.imm_data.ok
 365         if imm_ok:
 366             imm = yield self.dec2.e.imm_data.data
 367             inputs.append(SelectableInt(imm, 64))
 368         assert len(outputs) >= 1
 369         print ("outputs", repr(outputs))
 370         if isinstance(outputs, list) or isinstance(outputs, tuple):
 371             output = outputs[0]
 372         else:
 373             output = outputs
 374         gts = []
 375         for x in inputs:
 376             print ("gt input", x, output)
 377             gt = (x > output)
 378             gts.append(gt)
 379         print(gts)
 380         cy = 1 if any(gts) else 0
 381         if not (1 & already_done):
 382             self.spr['XER'][XER_bits['CA']] = cy
 383
 384         print ("inputs", inputs)
 385         # 32 bit carry
 386         gts = []
 387         for x in inputs:
 388             print ("input", x, output)
 389             gt = (x[32:64] > output[32:64]) == SelectableInt(1, 1)
 390             gts.append(gt)
 391         cy32 = 1 if any(gts) else 0
 392         if not (2 & already_done):
 393             self.spr['XER'][XER_bits['CA32']] = cy32
 394
 395     def handle_overflow(self, inputs, outputs, div_overflow):
 396         inv_a = yield self.dec2.e.invert_a
 397         if inv_a:
 398             inputs[0] = ~inputs[0]
 399
 400         imm_ok = yield self.dec2.e.imm_data.ok
 401         if imm_ok:
 402             imm = yield self.dec2.e.imm_data.data
 403             inputs.append(SelectableInt(imm, 64))
 404         assert len(outputs) >= 1
 405         print ("handle_overflow", inputs, outputs, div_overflow)
 406         if len(inputs) < 2 and div_overflow != 1:
 407             return
 408
 409         # div overflow is different: it's returned by the pseudo-code
 410         # because it's more complex than can be done by analysing the output
 411         if div_overflow == 1:
 412             ov, ov32 = 1, 1
 413         # arithmetic overflow can be done by analysing the input and output
 414         elif len(inputs) >= 2:
 415             output = outputs[0]
 416
 417             # OV (64-bit)
 418             input_sgn = [exts(x.value, x.bits) < 0 for x in inputs]
 419             output_sgn = exts(output.value, output.bits) < 0
 420             ov = 1 if input_sgn[0] == input_sgn[1] and \
 421                 output_sgn != input_sgn[0] else 0
 422
 423             # OV (32-bit)
 424             input32_sgn = [exts(x.value, 32) < 0 for x in inputs]
 425             output32_sgn = exts(output.value, 32) < 0
 426             ov32 = 1 if input32_sgn[0] == input32_sgn[1] and \
 427                 output32_sgn != input32_sgn[0] else 0
 428
 429         self.spr['XER'][XER_bits['OV']] = ov
 430         self.spr['XER'][XER_bits['OV32']] = ov32
 431         so = self.spr['XER'][XER_bits['SO']]
 432         so = so | ov
 433         self.spr['XER'][XER_bits['SO']] = so
 434
 435     def handle_comparison(self, outputs):
 436         out = outputs[0]
 437         out = exts(out.value, out.bits)
 438         zero = SelectableInt(out == 0, 1)
 439         positive = SelectableInt(out > 0, 1)
 440         negative = SelectableInt(out < 0, 1)
 441         SO = self.spr['XER'][XER_bits['SO']]
 442         cr_field = selectconcat(negative, positive, zero, SO)
 443         self.crl[0].eq(cr_field)
 444
 445     def set_pc(self, pc_val):
 446         self.namespace['NIA'] = SelectableInt(pc_val, 64)
 447         self.pc.update(self.namespace)
 448
 449     def setup_one(self):
 450         """set up one instruction
 451         """
 452         if self.respect_pc:
 453             pc = self.pc.CIA.value
 454         else:
 455             pc = self.fake_pc
 456         self._pc = pc
 457         ins = self.imem.ld(pc, 4, False, True)
 458         if ins is None:
 459             raise KeyError("no instruction at 0x%x" % pc)
 460         print("setup: 0x%x 0x%x %s" % (pc, ins & 0xffffffff, bin(ins)))
 461         print ("NIA, CIA", self.pc.CIA.value, self.pc.NIA.value)
 462
 463         yield self.dec2.dec.raw_opcode_in.eq(ins & 0xffffffff)
 464         yield self.dec2.dec.bigendian.eq(0)  # little / big?
 465
 466     def execute_one(self):
 467         """execute one instruction
 468         """
 469         # get the disassembly code for this instruction
 470         code = self.disassembly[self._pc]
 471         print("sim-execute", hex(self._pc), code)
 472         opname = code.split(' ')[0]
 473         yield from self.call(opname)
 474
 475         if not self.respect_pc:
 476             self.fake_pc += 4
 477         print ("NIA, CIA", self.pc.CIA.value, self.pc.NIA.value)
 478
 479     def get_assembly_name(self):
 480         # TODO, asmregs is from the spec, e.g. add RT,RA,RB
 481         # see http://bugs.libre-riscv.org/show_bug.cgi?id=282
 482         asmcode = yield self.dec2.dec.op.asmcode
 483         asmop = insns.get(asmcode, None)
 484
 485         # sigh reconstruct the assembly instruction name
 486         ov_en = yield self.dec2.e.oe.oe
 487         ov_ok = yield self.dec2.e.oe.ok
 488         if ov_en & ov_ok:
 489             asmop += "."
 490         lk = yield self.dec2.e.lk
 491         if lk:
 492             asmop += "l"
 493         int_op = yield self.dec2.dec.op.internal_op
 494         print ("int_op", int_op)
 495         if int_op in [InternalOp.OP_B.value, InternalOp.OP_BC.value]:
 496             AA = yield self.dec2.dec.fields.FormI.AA[0:-1]
 497             print ("AA", AA)
 498             if AA:
 499                 asmop += "a"
 500         if int_op == InternalOp.OP_MFCR.value:
 501             dec_insn = yield self.dec2.e.insn
 502             if dec_insn & (1<<20) != 0: # sigh
 503                 asmop = 'mfocrf'
 504             else:
 505                 asmop = 'mfcr'
 506         # XXX TODO: for whatever weird reason this doesn't work
 507         # https://bugs.libre-soc.org/show_bug.cgi?id=390
 508         if int_op == InternalOp.OP_MTCRF.value:
 509             dec_insn = yield self.dec2.e.insn
 510             if dec_insn & (1<<20) != 0: # sigh
 511                 asmop = 'mtocrf'
 512             else:
 513                 asmop = 'mtcrf'
 514         return asmop
 515
 516     def call(self, name):
 517         # TODO, asmregs is from the spec, e.g. add RT,RA,RB
 518         # see http://bugs.libre-riscv.org/show_bug.cgi?id=282
 519         asmop = yield from self.get_assembly_name()
 520         print  ("call", name, asmop)
 521         if name not in ['mtcrf', 'mtocrf']:
 522             assert name == asmop, "name %s != %s" % (name, asmop)
 523
 524         info = self.instrs[name]
 525         yield from self.prep_namespace(info.form, info.op_fields)
 526
 527         # preserve order of register names
 528         input_names = create_args(list(info.read_regs) + list(info.uninit_regs))
 529         print(input_names)
 530
 531         # main registers (RT, RA ...)
 532         inputs = []
 533         for name in input_names:
 534             regnum = yield getattr(self.decoder, name)
 535             regname = "_" + name
 536             self.namespace[regname] = regnum
 537             print('reading reg %d' % regnum)
 538             inputs.append(self.gpr(regnum))
 539
 540         # "special" registers
 541         for special in info.special_regs:
 542             if special in special_sprs:
 543                 inputs.append(self.spr[special])
 544             else:
 545                 inputs.append(self.namespace[special])
 546
 547         print(inputs)
 548         results = info.func(self, *inputs)
 549         print(results)
 550
 551         # detect if CA/CA32 already in outputs (sra*, basically)
 552         already_done = 0
 553         if info.write_regs:
 554             output_names = create_args(info.write_regs)
 555             for name in output_names:
 556                 if name == 'CA':
 557                     already_done |= 1
 558                 if name == 'CA32':
 559                     already_done |= 2
 560
 561         print ("carry already done?", bin(already_done))
 562         carry_en = yield self.dec2.e.output_carry
 563         if carry_en:
 564             yield from self.handle_carry_(inputs, results, already_done)
 565
 566         # detect if overflow was in return result
 567         overflow = None
 568         if info.write_regs:
 569             for name, output in zip(output_names, results):
 570                 if name == 'overflow':
 571                     overflow = output
 572
 573         ov_en = yield self.dec2.e.oe.oe
 574         ov_ok = yield self.dec2.e.oe.ok
 575         print ("internal overflow", overflow)
 576         if ov_en & ov_ok:
 577             yield from self.handle_overflow(inputs, results, overflow)
 578
 579         rc_en = yield self.dec2.e.rc.data
 580         if rc_en:
 581             self.handle_comparison(results)
 582
 583         # any modified return results?
 584         if info.write_regs:
 585             for name, output in zip(output_names, results):
 586                 if name == 'overflow': # ignore, done already (above)
 587                     continue
 588                 if isinstance(output, int):
 589                     output = SelectableInt(output, 256)
 590                 if name in ['CA', 'CA32']:
 591                     if carry_en:
 592                         print ("writing %s to XER" % name, output)
 593                         self.spr['XER'][XER_bits[name]] = output.value
 594                     else:
 595                         print ("NOT writing %s to XER" % name, output)
 596                 elif name in info.special_regs:
 597                     print('writing special %s' % name, output, special_sprs)
 598                     if name in special_sprs:
 599                         self.spr[name] = output
 600                     else:
 601                         self.namespace[name].eq(output)
 602                     if name == 'MSR':
 603                         print ('msr written', hex(self.msr.value))
 604                 else:
 605                     regnum = yield getattr(self.decoder, name)
 606                     print('writing reg %d %s' % (regnum, str(output)))
 607                     if output.bits > 64:
 608                         output = SelectableInt(output.value, 64)
 609                     self.gpr[regnum] = output
 610
 611         # update program counter
 612         self.pc.update(self.namespace)
 613
 614
 615 def inject():
 616     """Decorator factory.
 617
 618     this decorator will "inject" variables into the function's namespace,
 619     from the *dictionary* in self.namespace.  it therefore becomes possible
 620     to make it look like a whole stack of variables which would otherwise
 621     need "self." inserted in front of them (*and* for those variables to be
 622     added to the instance) "appear" in the function.
 623
 624     "self.namespace['SI']" for example becomes accessible as just "SI" but
 625     *only* inside the function, when decorated.
 626     """
 627     def variable_injector(func):
 628         @wraps(func)
 629         def decorator(*args, **kwargs):
 630             try:
 631                 func_globals = func.__globals__  # Python 2.6+
 632             except AttributeError:
 633                 func_globals = func.func_globals  # Earlier versions.
 634
 635             context = args[0].namespace # variables to be injected
 636             saved_values = func_globals.copy()  # Shallow copy of dict.
 637             func_globals.update(context)
 638             result = func(*args, **kwargs)
 639             args[0].namespace = func_globals
 640             #exec (func.__code__, func_globals)
 641
 642             #finally:
 643             #    func_globals = saved_values  # Undo changes.
 644
 645             return result
 646
 647         return decorator
 648
 649     return variable_injector
 650