4532

Make segment names a separate transform.

1 files changed, 31 insertions, 0 deletions

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
+  }
+}