path: root/subx/015immediate_addressing.cc

//: instructions that (immediately) contain an argument to act with

:(before "End Initialize Op Names")
put_new(Name, "81", "combine rm32 with imm32 based on subop (add/sub/and/or/xor/cmp)");

:(scenario add_imm32_to_r32)
% Reg[EBX].i = 1;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  c3                          0a 0b 0c 0d  # add 0x0d0c0b0a to EBX
# ModR/M in binary: 11 (direct mode) 000 (add imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x0d0c0b0a
+run: subop add
+run: storing 0x0d0c0b0b

:(before "End Single-Byte Opcodes")
case 0x81: {  // combine imm32 with r/m32
  trace(Callstack_depth+1, "run") << "combine imm32 with r/m32" << end();
  const uint8_t modrm = next();
  int32_t* arg1 = effective_address(modrm);
  const int32_t arg2 = next32();
  trace(Callstack_depth+1, "run") << "imm32 is 0x" << HEXWORD << arg2 << end();
  const uint8_t subop = (modrm>>3)&0x7;  // middle 3 'reg opcode' bits
  switch (subop) {
  case 0:
    trace(Callstack_depth+1, "run") << "subop add" << end();
    BINARY_ARITHMETIC_OP(+, *arg1, arg2);
    break;
  // End Op 81 Subops
  default:
    cerr << "unrecognized subop for opcode 81: " << NUM(subop) << '\n';
    exit(1);
  }
  break;
}

//:

:(scenario add_imm32_to_mem_at_r32)
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  03                          0a 0b 0c 0d  # add 0x0d0c0b0a to *EBX
# ModR/M in binary: 00 (indirect mode) 000 (add imm32) 011 (dest EBX)
== 0x2000  # data segment
01 00 00 00  # 1
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x0d0c0b0a
+run: subop add
+run: storing 0x0d0c0b0b

//:: subtract

:(before "End Initialize Op Names")
put_new(Name, "2d", "subtract imm32 from EAX (sub)");

:(scenario subtract_imm32_from_eax)
% Reg[EAX].i = 0x0d0c0baa;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  2d                              0a 0b 0c 0d  # subtract 0x0d0c0b0a from EAX
+run: subtract imm32 0x0d0c0b0a from EAX
+run: storing 0x000000a0

:(before "End Single-Byte Opcodes")
case 0x2d: {  // subtract imm32 from EAX
  const int32_t arg2 = next32();
  trace(Callstack_depth+1, "run") << "subtract imm32 0x" << HEXWORD << arg2 << " from EAX" << end();
  BINARY_ARITHMETIC_OP(-, Reg[EAX].i, arg2);
  break;
}

//:

:(scenario subtract_imm32_from_mem_at_r32)
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  2b                          01 00 00 00  # subtract 1 from *EBX
# ModR/M in binary: 00 (indirect mode) 101 (subtract imm32) 011 (dest EBX)
== 0x2000  # data segment
0a 00 00 00  # 10
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x00000001
+run: subop subtract
+run: storing 0x00000009

:(before "End Op 81 Subops")
case 5: {
  trace(Callstack_depth+1, "run") << "subop subtract" << end();
  BINARY_ARITHMETIC_OP(-, *arg1, arg2);
  break;
}

//:

:(scenario subtract_imm32_from_r32)
% Reg[EBX].i = 10;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  eb                          01 00 00 00  # subtract 1 from EBX
# ModR/M in binary: 11 (direct mode) 101 (subtract imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x00000001
+run: subop subtract
+run: storing 0x00000009

//:: shift left

:(before "End Initialize Op Names")
put_new(Name, "c1", "shift rm32 by imm8 bits depending on subop (sal/sar/shl/shr)");

:(scenario shift_left_r32_with_imm8)
% Reg[EBX].i = 13;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c1  e3                          01          # negate EBX
# ModR/M in binary: 11 (direct mode) 100 (subop shift left) 011 (dest EBX)
+run: operate on r/m32
+run: r/m32 is EBX
+run: subop: shift left by CL bits
+run: storing 0x0000001a

:(before "End Single-Byte Opcodes")
case 0xc1: {
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "operate on r/m32" << end();
  int32_t* arg1 = effective_address(modrm);
  const uint8_t subop = (modrm>>3)&0x7;  // middle 3 'reg opcode' bits
  switch (subop) {
  case 4: {  // shift left r/m32 by CL
    trace(Callstack_depth+1, "run") << "subop: shift left by CL bits" << end();
    uint8_t count = next() & 0x1f;
    // OF is only defined if count is 1
    if (count == 1) {
      bool msb = (*arg1 & 0x80000000) >> 1;
      bool pnsb = (*arg1 & 0x40000000);
      OF = (msb != pnsb);
    }
    *arg1 = (*arg1 << count);
    ZF = (*arg1 == 0);
    SF = (*arg1 < 0);
    trace(Callstack_depth+1, "run") << "storing 0x" << HEXWORD << *arg1 << end();
    break;
  }
  // End Op c1 Subops
  default:
    cerr << "unrecognized subop for opcode c1: " << NUM(subop) << '\n';
    exit(1);
  }
  break;
}

//:: shift right arithmetic

:(scenario shift_right_arithmetic_r32_with_imm8)
% Reg[EBX].i = 26;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c1  fb                          01          # negate EBX
# ModR/M in binary: 11 (direct mode) 111 (subop shift right arithmetic) 011 (dest EBX)
+run: operate on r/m32
+run: r/m32 is EBX
+run: subop: shift right by CL bits, while preserving sign
+run: storing 0x0000000d

:(before "End Op c1 Subops")
case 7: {  // shift right r/m32 by CL, preserving sign
  trace(Callstack_depth+1, "run") << "subop: shift right by CL bits, while preserving sign" << end();
  uint8_t count = next() & 0x1f;
  *arg1 = (*arg1 >> count);
  ZF = (*arg1 == 0);
  SF = (*arg1 < 0);
  // OF is only defined if count is 1
  if (count == 1) OF = false;
  trace(Callstack_depth+1, "run") << "storing 0x" << HEXWORD << *arg1 << end();
  break;
}

:(scenario shift_right_arithmetic_odd_r32_with_imm8)
% Reg[EBX].i = 27;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c1  fb                          01          # negate EBX
# ModR/M in binary: 11 (direct mode) 111 (subop shift right arithmetic) 011 (dest EBX)
+run: operate on r/m32
+run: r/m32 is EBX
+run: subop: shift right by CL bits, while preserving sign
# result: 13
+run: storing 0x0000000d

:(scenario shift_right_arithmetic_negative_r32_with_imm8)
% Reg[EBX].i = 0xfffffffd;  // -3
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c1  fb                          01          # negate EBX
# ModR/M in binary: 11 (direct mode) 111 (subop shift right arithmetic) 011 (dest EBX)
+run: operate on r/m32
+run: r/m32 is EBX
+run: subop: shift right by CL bits, while preserving sign
# result: -2
+run: storing 0xfffffffe

//:: shift right logical

:(scenario shift_right_logical_r32_with_imm8)
% Reg[EBX].i = 26;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c1  eb                          01          # negate EBX
# ModR/M in binary: 11 (direct mode) 101 (subop shift right logical) 011 (dest EBX)
+run: operate on r/m32
+run: r/m32 is EBX
+run: subop: shift right by CL bits, while padding zeroes
+run: storing 0x0000000d

:(before "End Op c1 Subops")
case 5: {  // shift right r/m32 by CL, preserving sign
  trace(Callstack_depth+1, "run") << "subop: shift right by CL bits, while padding zeroes" << end();
  uint8_t count = next() & 0x1f;
  // OF is only defined if count is 1
  if (count == 1) {
    bool msb = (*arg1 & 0x80000000) >> 1;
    bool pnsb = (*arg1 & 0x40000000);
    OF = (msb != pnsb);
  }
  uint32_t* uarg1 = reinterpret_cast<uint32_t*>(arg1);
  *uarg1 = (*uarg1 >> count);
  ZF = (*uarg1 == 0);
  // result is always positive by definition
  SF = false;
  trace(Callstack_depth+1, "run") << "storing 0x" << HEXWORD << *arg1 << end();
  break;
}

:(scenario shift_right_logical_odd_r32_with_imm8)
% Reg[EBX].i = 27;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c1  eb                          01          # negate EBX
# ModR/M in binary: 11 (direct mode) 101 (subop shift right logical) 011 (dest EBX)
+run: operate on r/m32
+run: r/m32 is EBX
+run: subop: shift right by CL bits, while padding zeroes
# result: 13
+run: storing 0x0000000d

:(scenario shift_right_logical_negative_r32_with_imm8)
% Reg[EBX].i = 0xfffffffd;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c1  eb                          01          # negate EBX
# ModR/M in binary: 11 (direct mode) 101 (subop shift right logical) 011 (dest EBX)
+run: operate on r/m32
+run: r/m32 is EBX
+run: subop: shift right by CL bits, while padding zeroes
+run: storing 0x7ffffffe

//:: and

:(before "End Initialize Op Names")
put_new(Name, "25", "EAX = bitwise AND of imm32 with EAX (and)");

:(scenario and_imm32_with_eax)
% Reg[EAX].i = 0xff;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  25                              0a 0b 0c 0d  # and 0x0d0c0b0a with EAX
+run: and imm32 0x0d0c0b0a with EAX
+run: storing 0x0000000a

:(before "End Single-Byte Opcodes")
case 0x25: {  // and imm32 with EAX
  const int32_t arg2 = next32();
  trace(Callstack_depth+1, "run") << "and imm32 0x" << HEXWORD << arg2 << " with EAX" << end();
  BINARY_BITWISE_OP(&, Reg[EAX].i, arg2);
  break;
}

//:

:(scenario and_imm32_with_mem_at_r32)
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  23                          0a 0b 0c 0d  # and 0x0d0c0b0a with *EBX
# ModR/M in binary: 00 (indirect mode) 100 (and imm32) 011 (dest EBX)
== 0x2000  # data segment
ff 00 00 00  # 0xff
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x0d0c0b0a
+run: subop and
+run: storing 0x0000000a

:(before "End Op 81 Subops")
case 4: {
  trace(Callstack_depth+1, "run") << "subop and" << end();
  BINARY_BITWISE_OP(&, *arg1, arg2);
  break;
}

//:

:(scenario and_imm32_with_r32)
% Reg[EBX].i = 0xff;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  e3                          0a 0b 0c 0d  # and 0x0d0c0b0a with EBX
# ModR/M in binary: 11 (direct mode) 100 (and imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x0d0c0b0a
+run: subop and
+run: storing 0x0000000a

//:: or

:(before "End Initialize Op Names")
put_new(Name, "0d", "EAX = bitwise OR of imm32 with EAX (or)");

:(scenario or_imm32_with_eax)
% Reg[EAX].i = 0xd0c0b0a0;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  0d                              0a 0b 0c 0d  # or 0x0d0c0b0a with EAX
+run: or imm32 0x0d0c0b0a with EAX
+run: storing 0xddccbbaa

:(before "End Single-Byte Opcodes")
case 0x0d: {  // or imm32 with EAX
  const int32_t arg2 = next32();
  trace(Callstack_depth+1, "run") << "or imm32 0x" << HEXWORD << arg2 << " with EAX" << end();
  BINARY_BITWISE_OP(|, Reg[EAX].i, arg2);
  break;
}

//:

:(scenario or_imm32_with_mem_at_r32)
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  0b                          0a 0b 0c 0d  # or 0x0d0c0b0a with *EBX
# ModR/M in binary: 00 (indirect mode) 001 (or imm32) 011 (dest EBX)
== 0x2000  # data segment
a0 b0 c0 d0  # 0xd0c0b0a0
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x0d0c0b0a
+run: subop or
+run: storing 0xddccbbaa

:(before "End Op 81 Subops")
case 1: {
  trace(Callstack_depth+1, "run") << "subop or" << end();
  BINARY_BITWISE_OP(|, *arg1, arg2);
  break;
}

:(scenario or_imm32_with_r32)
% Reg[EBX].i = 0xd0c0b0a0;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  cb                          0a 0b 0c 0d  # or 0x0d0c0b0a with EBX
# ModR/M in binary: 11 (direct mode) 001 (or imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x0d0c0b0a
+run: subop or
+run: storing 0xddccbbaa

//:: xor

:(before "End Initialize Op Names")
put_new(Name, "35", "EAX = bitwise XOR of imm32 with EAX (xor)");

:(scenario xor_imm32_with_eax)
% Reg[EAX].i = 0xddccb0a0;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  35                              0a 0b 0c 0d  # xor 0x0d0c0b0a with EAX
+run: xor imm32 0x0d0c0b0a with EAX
+run: storing 0xd0c0bbaa

:(before "End Single-Byte Opcodes")
case 0x35: {  // xor imm32 with EAX
  const int32_t arg2 = next32();
  trace(Callstack_depth+1, "run") << "xor imm32 0x" << HEXWORD << arg2 << " with EAX" << end();
  BINARY_BITWISE_OP(^, Reg[EAX].i, arg2);
  break;
}

//:

:(scenario xor_imm32_with_mem_at_r32)
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  33                          0a 0b 0c 0d  # xor 0x0d0c0b0a with *EBX
# ModR/M in binary: 00 (indirect mode) 110 (xor imm32) 011 (dest EBX)
== 0x2000  # data segment
a0 b0 c0 d0  # 0xd0c0b0a0
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x0d0c0b0a
+run: subop xor
+run: storing 0xddccbbaa

:(before "End Op 81 Subops")
case 6: {
  trace(Callstack_depth+1, "run") << "subop xor" << end();
  BINARY_BITWISE_OP(^, *arg1, arg2);
  break;
}

:(scenario xor_imm32_with_r32)
% Reg[EBX].i = 0xd0c0b0a0;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  f3                          0a 0b 0c 0d  # xor 0x0d0c0b0a with EBX
# ModR/M in binary: 11 (direct mode) 110 (xor imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x0d0c0b0a
+run: subop xor
+run: storing 0xddccbbaa

//:: compare (cmp)

:(before "End Initialize Op Names")
put_new(Name, "3d", "compare: set SF if EAX < imm32 (cmp)");

:(scenario compare_imm32_with_eax_greater)
% Reg[EAX].i = 0x0d0c0b0a;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  3d                              07 0b 0c 0d  # compare 0x0d0c0b07 with EAX
+run: compare EAX and imm32 0x0d0c0b07
+run: SF=0; ZF=0; OF=0

:(before "End Single-Byte Opcodes")
case 0x3d: {  // compare EAX with imm32
  const int32_t arg1 = Reg[EAX].i;
  const int32_t arg2 = next32();
  trace(Callstack_depth+1, "run") << "compare EAX and imm32 0x" << HEXWORD << arg2 << end();
  const int32_t tmp1 = arg1 - arg2;
  SF = (tmp1 < 0);
  ZF = (tmp1 == 0);
  const int64_t tmp2 = arg1 - arg2;
  OF = (tmp1 != tmp2);
  trace(Callstack_depth+1, "run") << "SF=" << SF << "; ZF=" << ZF << "; OF=" << OF << end();
  break;
}

:(scenario compare_imm32_with_eax_lesser)
% Reg[EAX].i = 0x0d0c0b07;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  3d                              0a 0b 0c 0d  # compare 0x0d0c0b0a with EAX
+run: compare EAX and imm32 0x0d0c0b0a
+run: SF=1; ZF=0; OF=0

:(scenario compare_imm32_with_eax_equal)
% Reg[EAX].i = 0x0d0c0b0a;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  3d                              0a 0b 0c 0d  # compare 0x0d0c0b0a with EAX
+run: compare EAX and imm32 0x0d0c0b0a
+run: SF=0; ZF=1; OF=0

//:

:(scenario compare_imm32_with_r32_greater)
% Reg[EBX].i = 0x0d0c0b0a;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  fb                          07 0b 0c 0d  # compare 0x0d0c0b07 with EBX
# ModR/M in binary: 11 (direct mode) 111 (compare imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x0d0c0b07
+run: SF=0; ZF=0; OF=0

:(before "End Op 81 Subops")
case 7: {
  trace(Callstack_depth+1, "run") << "subop compare" << end();
  const int32_t tmp1 = *arg1 - arg2;
  SF = (tmp1 < 0);
  ZF = (tmp1 == 0);
  const int64_t tmp2 = *arg1 - arg2;
  OF = (tmp1 != tmp2);
  trace(Callstack_depth+1, "run") << "SF=" << SF << "; ZF=" << ZF << "; OF=" << OF << end();
  break;
}

:(scenario compare_imm32_with_r32_lesser)
% Reg[EBX].i = 0x0d0c0b07;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  fb                          0a 0b 0c 0d  # compare 0x0d0c0b0a with EBX
# ModR/M in binary: 11 (direct mode) 111 (compare imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x0d0c0b0a
+run: SF=1; ZF=0; OF=0

:(scenario compare_imm32_with_r32_equal)
% Reg[EBX].i = 0x0d0c0b0a;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  81  fb                          0a 0b 0c 0d  # compare 0x0d0c0b0a with EBX
# ModR/M in binary: 11 (direct mode) 111 (compare imm32) 011 (dest EBX)
+run: combine imm32 with r/m32
+run: r/m32 is EBX
+run: imm32 is 0x0d0c0b0a
+run: SF=0; ZF=1; OF=0

:(scenario compare_imm32_with_mem_at_r32_greater)
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  3b                          07 0b 0c 0d  # compare 0x0d0c0b07 with *EBX
# ModR/M in binary: 00 (indirect mode) 111 (compare imm32) 011 (dest EBX)
== 0x2000  # data segment
0a 0b 0c 0d  # 0x0d0c0b0a
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x0d0c0b07
+run: SF=0; ZF=0; OF=0

:(scenario compare_imm32_with_mem_at_r32_lesser)
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  3b                          0a 0b 0c 0d  # compare 0x0d0c0b0a with *EBX
# ModR/M in binary: 00 (indirect mode) 111 (compare imm32) 011 (dest EBX)
== 0x2000  # data segment
07 0b 0c 0d  # 0x0d0c0b07
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x0d0c0b0a
+run: SF=1; ZF=0; OF=0

:(scenario compare_imm32_with_mem_at_r32_equal)
% Reg[EBX].i = 0x0d0c0b0a;
% Reg[EBX].i = 0x2000;
== 0x01  # code segment
# op  ModR/M  SIB   displacement  immediate
  81  3b                          0a 0b 0c 0d  # compare 0x0d0c0b0a with *EBX
# ModR/M in binary: 00 (indirect mode) 111 (compare imm32) 011 (dest EBX)
== 0x2000  # data segment
0a 0b 0c 0d  # 0x0d0c0b0a
+run: combine imm32 with r/m32
+run: effective address is 0x00002000 (EBX)
+run: imm32 is 0x0d0c0b0a
+run: SF=0; ZF=1; OF=0

//:: copy (mov)

:(before "End Initialize Op Names")
put_new(Name, "b8", "copy imm32 to EAX (mov)");
put_new(Name, "b9", "copy imm32 to ECX (mov)");
put_new(Name, "ba", "copy imm32 to EDX (mov)");
put_new(Name, "bb", "copy imm32 to EBX (mov)");
put_new(Name, "bc", "copy imm32 to ESP (mov)");
put_new(Name, "bd", "copy imm32 to EBP (mov)");
put_new(Name, "be", "copy imm32 to ESI (mov)");
put_new(Name, "bf", "copy imm32 to EDI (mov)");

:(scenario copy_imm32_to_r32)
== 0x1
# op  ModR/M  SIB   displacement  immediate
  bb                              0a 0b 0c 0d  # copy 0x0d0c0b0a to EBX
+run: copy imm32 0x0d0c0b0a to EBX

:(before "End Single-Byte Opcodes")
case 0xb8:
case 0xb9:
case 0xba:
case 0xbb:
case 0xbc:
case 0xbd:
case 0xbe:
case 0xbf: {  // copy imm32 to r32
  const uint8_t rdest = op & 0x7;
  const int32_t src = next32();
  trace(Callstack_depth+1, "run") << "copy imm32 0x" << HEXWORD << src << " to " << rname(rdest) << end();
  Reg[rdest].i = src;
  break;
}

//:

:(before "End Initialize Op Names")
put_new(Name, "c7", "copy imm32 to rm32 (mov)");

:(scenario copy_imm32_to_mem_at_r32)
% Reg[EBX].i = 0x60;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  c7  03                          0a 0b 0c 0d  # copy 0x0d0c0b0a to *EBX
# ModR/M in binary: 00 (indirect mode) 000 (unused) 011 (dest EBX)
+run: copy imm32 to r/m32
+run: effective address is 0x00000060 (EBX)
+run: imm32 is 0x0d0c0b0a

:(before "End Single-Byte Opcodes")
case 0xc7: {  // copy imm32 to r32
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "copy imm32 to r/m32" << end();
  const uint8_t subop = (modrm>>3)&0x7;  // middle 3 'reg opcode' bits
  if (subop != 0) {
    cerr << "unrecognized subop for opcode c7: " << NUM(subop) << " (only 0/copy currently implemented)\n";
    exit(1);
  }
  int32_t* dest = effective_address(modrm);
  const int32_t src = next32();
  trace(Callstack_depth+1, "run") << "imm32 is 0x" << HEXWORD << src << end();
  *dest = src;
  break;
}

//:: push

:(before "End Initialize Op Names")
put_new(Name, "68", "push imm32 to stack (push)");

:(scenario push_imm32)
% Reg[ESP].u = 0x14;
== 0x1
# op  ModR/M  SIB   displacement  immediate
  68                              af 00 00 00  # push *EAX to stack
+run: push imm32 0x000000af
+run: ESP is now 0x00000010
+run: contents at ESP: 0x000000af

:(before "End Single-Byte Opcodes")
case 0x68: {
  const uint32_t val = static_cast<uint32_t>(next32());
  trace(Callstack_depth+1, "run") << "push imm32 0x" << HEXWORD << val << end();
//?   cerr << "push: " << val << " => " << Reg[ESP].u << '\n';
  push(val);
  trace(Callstack_depth+1, "run") << "ESP is now 0x" << HEXWORD << Reg[ESP].u << end();
  trace(Callstack_depth+1, "run") << "contents at ESP: 0x" << HEXWORD << read_mem_u32(Reg[ESP].u) << end();
  break;
}