1 files changed, 155 insertions, 0 deletions
diff --git a/linux/bootstrap/016index_addressing.cc b/linux/bootstrap/016index_addressing.cc
new file mode 100644
index 00000000..f6c6f2aa
--- /dev/null
+++ b/linux/bootstrap/016index_addressing.cc
@@ -0,0 +1,155 @@
+//: operating on memory at the address provided by some register plus optional scale and offset
+
+:(code)
+void test_add_r32_to_mem_at_rm32_with_sib() {
+  Reg[EBX].i = 0x10;
+  Reg[EAX].i = 0x2000;
+  run(
+      "== code 0x1\n"
+      // op     ModR/M  SIB   displacement  immediate
+      "  01     1c      20                              \n"  // add EBX to *EAX
+      // ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB)
+      // SIB in binary: 00 (scale 1) 100 (no index) 000 (base EAX)
+      "== data 0x2000\n"
+      "01 00 00 00\n"  // 1
+  );
+  CHECK_TRACE_CONTENTS(
+      "run: add EBX to r/m32\n"
+      "run: effective address is initially 0x00002000 (EAX)\n"
+      "run: effective address is 0x00002000\n"
+      "run: storing 0x00000011\n"
+  );
+}
+
+:(before "End Mod 0 Special-cases(addr)")
+case 4:  // exception: mod 0b00 rm 0b100 => incoming SIB (scale-index-base) byte
+  addr = effective_address_from_sib(mod);
+  break;
+:(code)
+uint32_t effective_address_from_sib(uint8_t mod) {
+  const uint8_t sib = next();
+  const uint8_t base = sib&0x7;
+  uint32_t addr = 0;
+  if (base != EBP || mod != 0) {
+    addr = Reg[base].u;
+    trace(Callstack_depth+1, "run") << "effective address is initially 0x" << HEXWORD << addr << " (" << rname(base) << ")" << end();
+  }
+  else {
+    // base == EBP && mod == 0
+    addr = next32();  // ignore base
+    trace(Callstack_depth+1, "run") << "effective address is initially 0x" << HEXWORD << addr << " (disp32)" << end();
+  }
+  const uint8_t index = (sib>>3)&0x7;
+  if (index == ESP) {
+    // ignore index and scale
+    trace(Callstack_depth+1, "run") << "effective address is 0x" << HEXWORD << addr << end();
+  }
+  else {
+    const uint8_t scale = (1 << (sib>>6));
+    addr += Reg[index].i*scale;  // treat index register as signed. Maybe base as well? But we'll always ensure it's non-negative.
+    trace(Callstack_depth+1, "run") << "effective address is 0x" << HEXWORD << addr << " (after adding " << rname(index) << "*" << NUM(scale) << ")" << end();
+  }
+  return addr;
+}
+
+:(code)
+void test_add_r32_to_mem_at_base_r32_index_r32() {
+  Reg[EBX].i = 0x10;  // source
+  Reg[EAX].i = 0x1ffe;  // dest base
+  Reg[ECX].i = 0x2;  // dest index
+  run(
+      "== code 0x1\n"
+      // op     ModR/M  SIB   displacement  immediate
+      "  01     1c      08                              \n"  // add EBX to *(EAX+ECX)
+      // ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB)
+      // SIB in binary: 00 (scale 1) 001 (index ECX) 000 (base EAX)
+      "== data 0x2000\n"
+      "01 00 00 00\n"  // 1
+  );
+  CHECK_TRACE_CONTENTS(
+      "run: add EBX to r/m32\n"
+      "run: effective address is initially 0x00001ffe (EAX)\n"
+      "run: effective address is 0x00002000 (after adding ECX*1)\n"
+      "run: storing 0x00000011\n"
+  );
+}
+
+:(code)
+void test_add_r32_to_mem_at_displacement_using_sib() {
+  Reg[EBX].i = 0x10;  // source
+  run(
+      "== code 0x1\n"
+      // op     ModR/M  SIB   displacement  immediate
+      "  01     1c      25    00 20 00 00               \n"  // add EBX to *0x2000
+      // ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB)
+      // SIB in binary: 00 (scale 1) 100 (no index) 101 (not EBP but disp32)
+      "== data 0x2000\n"
+      "01 00 00 00\n"  // 1
+  );
+  CHECK_TRACE_CONTENTS(
+      "run: add EBX to r/m32\n"
+      "run: effective address is initially 0x00002000 (disp32)\n"
+      "run: effective address is 0x00002000\n"
+      "run: storing 0x00000011\n"
+  );
+}
+
+//:
+
+:(code)
+void test_add_r32_to_mem_at_base_r32_index_r32_plus_disp8() {
+  Reg[EBX].i = 0x10;  // source
+  Reg[EAX].i = 0x1ff9;  // dest base
+  Reg[ECX].i = 0x5;  // dest index
+  run(
+      "== code 0x1\n"
+      // op     ModR/M  SIB   displacement  immediate
+      "  01     5c      08    02                        \n"  // add EBX to *(EAX+ECX+2)
+      // ModR/M in binary: 01 (indirect+disp8 mode) 011 (src EBX) 100 (dest in SIB)
+      // SIB in binary: 00 (scale 1) 001 (index ECX) 000 (base EAX)
+      "== data 0x2000\n"
+      "01 00 00 00\n"  // 1
+  );
+  CHECK_TRACE_CONTENTS(
+      "run: add EBX to r/m32\n"
+      "run: effective address is initially 0x00001ff9 (EAX)\n"
+      "run: effective address is 0x00001ffe (after adding ECX*1)\n"
+      "run: effective address is 0x00002000 (after adding disp8)\n"
+      "run: storing 0x00000011\n"
+  );
+}
+
+:(before "End Mod 1 Special-cases(addr)")
+case 4:  // exception: mod 0b01 rm 0b100 => incoming SIB (scale-index-base) byte
+  addr = effective_address_from_sib(mod);
+  break;
+
+//:
+
+:(code)
+void test_add_r32_to_mem_at_base_r32_index_r32_plus_disp32() {
+  Reg[EBX].i = 0x10;  // source
+  Reg[EAX].i = 0x1ff9;  // dest base
+  Reg[ECX].i = 0x5;  // dest index
+  run(
+      "== code 0x1\n"
+      // op     ModR/M  SIB   displacement  immediate
+      "  01     9c      08    02 00 00 00               \n"  // add EBX to *(EAX+ECX+2)
+      // ModR/M in binary: 10 (indirect+disp32 mode) 011 (src EBX) 100 (dest in SIB)
+      // SIB in binary: 00 (scale 1) 001 (index ECX) 000 (base EAX)
+      "== data 0x2000\n"
+      "01 00 00 00\n"  // 1
+  );
+  CHECK_TRACE_CONTENTS(
+      "run: add EBX to r/m32\n"
+      "run: effective address is initially 0x00001ff9 (EAX)\n"
+      "run: effective address is 0x00001ffe (after adding ECX*1)\n"
+      "run: effective address is 0x00002000 (after adding disp32)\n"
+      "run: storing 0x00000011\n"
+  );
+}
+
+:(before "End Mod 2 Special-cases(addr)")
+case 4:  // exception: mod 0b10 rm 0b100 => incoming SIB (scale-index-base) byte
+  addr = effective_address_from_sib(mod);
+  break;