4532

Make segment names a separate transform.

2 files changed, 36 insertions, 28 deletions

diff --git a/subx/028translate.cc b/subx/028translate.cc
index cc41e715..4c2ba133 100644
--- a/subx/028translate.cc
+++ b/subx/028translate.cc
@@ -30,28 +30,12 @@ if (is_equal(argv[1], "translate")) {
   if (trace_contains_errors()) return 1;
   transform(p);
   if (trace_contains_errors()) return 1;
-  compute_segment_offsets(p);
   save_elf(p, argv[3]);
   if (trace_contains_errors()) unlink(argv[3]);
   return 0;
 }
 
-:(before "End segment Fields")
-uint32_t offset;
-:(before "End segment Constructor")
-offset = 0;
 :(code)
-void compute_segment_offsets(program& p) {
-  uint32_t p_offset = /*size of ehdr*/0x34 + SIZE(p.segments)*0x20/*size of each phdr*/;
-  uint32_t cumulative_segment_size = 0;
-  for (size_t i = 0;  i < p.segments.size();  ++i) {
-    segment& curr = p.segments.at(i);
-    curr.offset = p_offset + cumulative_segment_size;
-//?     cerr << "offset " << i << ": " << curr.offset << '\n';
-    cumulative_segment_size += num_words(curr);
-  }
-}
-
 // write out a program to a bare-bones ELF file
 void save_elf(const program& p, const char* filename) {
   ofstream out(filename, ios::binary);
@@ -61,12 +45,6 @@ void save_elf(const program& p, const char* filename) {
   out.close();
 }
 
-uint32_t start(const program& p, const int segment_index) {
-  const segment& seg = p.segments.at(segment_index);
-  if (seg.start != 0) return seg.start;  // if start is already initialized, use it
-  return CODE_START + SEGMENT_SIZE*segment_index + seg.offset;
-}
-
 void write_elf_header(ostream& out, const program& p) {
   char c = '\0';
 #define O(X)  c = (X); out.write(&c, sizeof(c))
@@ -86,7 +64,7 @@ void write_elf_header(ostream& out, const program& p) {
   // e_version
   O(0x01); O(0x00); O(0x00); O(0x00);
   // e_entry
-  int e_entry = start(p, /*segment*/0);  // convention
+  int e_entry = p.segments.at(0).start;  // convention
   emit(e_entry);
   // e_phoff -- immediately after ELF header
   int e_phoff = 0x34;
@@ -113,23 +91,22 @@ void write_elf_header(ostream& out, const program& p) {
   // e_shstrndx
   emit(dummy16);
 
+  uint32_t p_offset = /*size of ehdr*/0x34 + SIZE(p.segments)*0x20/*size of each phdr*/;
   for (int i = 0;  i < SIZE(p.segments);  ++i) {
-    const segment& curr = p.segments.at(i);
     //// phdr
     // p_type
     uint32_t p_type = 0x1;
     emit(p_type);
     // p_offset
-    uint32_t p_offset = curr.offset;
     emit(p_offset);
     // p_vaddr
-    uint32_t p_start = start(p, i);
+    uint32_t p_start = p.segments.at(i).start;
     emit(p_start);
     // p_paddr
     emit(p_start);
     // p_filesz
-    uint32_t size = num_words(curr);
-    assert(size < SEGMENT_SIZE);
+    uint32_t size = num_words(p.segments.at(i));
+    assert(p_offset + size < SEGMENT_SIZE);
     emit(size);
     // p_memsz
     emit(size);
diff --git a/subx/037compute_segment_address.cc b/subx/037compute_segment_address.cc
new file mode 100644
index 00000000..ee2b1bb4
--- /dev/null
+++ b/subx/037compute_segment_address.cc
@@ -0,0 +1,31 @@
+//: Start allowing us to not specify precise addresses for the start of each
+//: segment.
+//: This gives up a measure of control in placing code and data.
+
+:(scenario segment_name)
+% Mem_offset = CODE_START;
+== code
+05/add 0x0d0c0b0a/imm32  # add 0x0d0c0b0a to EAX
+# code starts at 0x08048000 + p_offset, which is 0x54 for a single-segment binary
++load: 0x08048054 -> 05
++load: 0x08048055 -> 0a
++load: 0x08048056 -> 0b
++load: 0x08048057 -> 0c
++load: 0x08048058 -> 0d
++run: add imm32 0x0d0c0b0a to reg EAX
++run: storing 0x0d0c0b0a
+
+:(before "End Level-2 Transforms")
+Transform.push_back(compute_segment_starts);
+
+:(code)
+void compute_segment_starts(program& p) {
+  uint32_t p_offset = /*size of ehdr*/0x34 + SIZE(p.segments)*0x20/*size of each phdr*/;
+  for (size_t i = 0;  i < p.segments.size();  ++i) {
+    segment& curr = p.segments.at(i);
+    if (curr.start == 0)
+      curr.start = CODE_START + i*SEGMENT_SIZE + p_offset;
+    p_offset += num_words(curr);
+    assert(p_offset < SEGMENT_SIZE);  // for now we get less and less available space in each successive segment
+  }
+}