From 1a48f95a870559112eb7d3a6ecf236c78db13f5b Mon Sep 17 00:00:00 2001
From: Kartik Agaram <vc@akkartik.com>
Date: Tue, 10 Jul 2018 20:27:21 -0700
Subject: [PATCH] 4338 - preliminary support for data segments

---
 subx/010core.cc                | 25 ++++++++++++++++++++-----
 subx/012indirect_addressing.cc |  5 ++++-
 subx/021translate.cc           |  6 +++---
 subx/022transform_immediate.cc | 11 +++++++++++
 4 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/subx/010core.cc b/subx/010core.cc
index f6c79a78..c881c52b 100644
--- a/subx/010core.cc
+++ b/subx/010core.cc
@@ -140,7 +140,7 @@ inline void write_mem_i32(uint32_t addr, int32_t val) {
 void run(string text_bytes) {
   // Begin run() For Scenarios
 //?   cerr << text_bytes << '\n';
-  load_program(text_bytes, 1);  // tests always assume a starting address of 1
+  load_program(text_bytes);
   EIP = 1;  // preserve null pointer
   while (EIP < End_of_program)
     run_one_instruction();
@@ -193,11 +193,13 @@ void run_one_instruction() {
   }
 }
 
-void load_program(const string& text_bytes, uint32_t addr) {
+void load_program(const string& text_bytes) {
   istringstream in(text_bytes);
-  load_program(in, addr);
+  load_program(in);
 }
-void load_program(istream& in, uint32_t addr) {
+void load_program(istream& in) {
+  uint32_t addr = 1;  // preserve null pointer
+  int segment_index = 0;
   while (has_data(in)) {
     string line_data;
     getline(in, line_data);
@@ -207,6 +209,18 @@ void load_program(istream& in, uint32_t addr) {
       string word;
       line >> word;
       if (word.empty()) continue;
+      if (word == "==") {
+        // assume the first segment contains code
+        if (segment_index == 1) End_of_program = addr;
+        ++segment_index;
+        // new segment
+        line >> std::hex >> addr;
+        break;  // skip rest of line
+      }
+      if (word[0] == ':') {
+        // metadata
+        break;
+      }
       if (word[0] == '#') {
         // comment
         break;
@@ -225,7 +239,8 @@ void load_program(istream& in, uint32_t addr) {
       addr++;
     }
   }
-  End_of_program = addr;
+  // convenience: allow zero segment headers; code then starts at address 1
+  if (segment_index == 0) End_of_program = addr;
 }
 
 inline uint8_t next() {
diff --git a/subx/012indirect_addressing.cc b/subx/012indirect_addressing.cc
index 2901f8d5..304467f7 100644
--- a/subx/012indirect_addressing.cc
+++ b/subx/012indirect_addressing.cc
@@ -1,12 +1,15 @@
 //: operating on memory at the address provided by some register
+//: we'll now start providing data in a separate segment
 
 :(scenario add_r32_to_mem_at_r32)
 % Reg[3].i = 0x10;
 % Reg[0].i = 0x60;
-% write_mem_i32(0x60, 1);
+== 0x01  # code segment
 # op  ModR/M  SIB   displacement  immediate
   01  18                                     # add EBX to *EAX
 # ModR/M in binary: 00 (indirect mode) 011 (src EAX) 000 (dest EAX)
+== 0x60  # data segment
+01 00 00 00  # 1
 +run: add EBX to r/m32
 +run: effective address is 0x60 (EAX)
 +run: storing 0x00000011
diff --git a/subx/021translate.cc b/subx/021translate.cc
index 6d0fb899..f658f6db 100644
--- a/subx/021translate.cc
+++ b/subx/021translate.cc
@@ -34,9 +34,9 @@ void perform_all_transforms(string& program) {
 void dump_elf(const string& program, const char* filename) {
   initialize_mem();
   // load program into memory, filtering out comments
-  load_program(program, 1);  // Not where 'program' should be loaded for running.
-                             // But we're not going to run it right now, so we
-                             // can load it anywhere.
+  load_program(program);  // Not where 'program' should be loaded for running.
+                          // But we're not going to run it right now, so we
+                          // can load it anywhere.
   // dump contents of memory into ELF binary
   ofstream out(filename, ios::binary);
   dump_elf_header(out);
diff --git a/subx/022transform_immediate.cc b/subx/022transform_immediate.cc
index 48f5dfa9..24539f10 100644
--- a/subx/022transform_immediate.cc
+++ b/subx/022transform_immediate.cc
@@ -32,6 +32,17 @@ void transform_immediate(const string& input, string& output) {
       string word;
       line >> word;
       if (word.empty()) continue;
+      if (word == "==") {
+        // new segment
+        uint32_t addr = 0;
+        line >> std::hex >> addr;
+        out << "== " << HEXWORD << addr;
+        break;  // skip rest of line
+      }
+      if (word[0] == ':') {
+        // skip line metadata
+        break;
+      }
       if (word[0] == '#') {
         // skip comment
         break;