From 8ba17d839eeca97bbf3947ce1995350b0858f233 Mon Sep 17 00:00:00 2001
From: Kartik Agaram <vc@akkartik.com>
Date: Fri, 12 Jul 2019 23:14:13 -0700
Subject: [PATCH] .

Snapshot at a random moment, showing a new debugging trick: hacking on
the C++ level to dump memory contents on specific labels.

For some reason label 'x' doesn't have a segment assigned by the time we
get to compute-addresses.
---
 subx/039debug.cc      | 15 ++++++++++++
 subx/apps/survey.subx | 57 +++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/subx/039debug.cc b/subx/039debug.cc
index a592e198..49c0b8b6 100644
--- a/subx/039debug.cc
+++ b/subx/039debug.cc
@@ -91,6 +91,21 @@ if (!Watch_this_effective_address.empty()) {
   put(Watch_points, Watch_this_effective_address, addr);
 }
 
+//: Special label that dumps regions of memory.
+//: Not a general mechanism; by the time you get here you're willing to hack
+//: on the emulator.
+:(after "Run One Instruction")
+if (contains_key(Symbol_name, EIP) && get(Symbol_name, EIP) == "$dump-stream-at-ESI")
+  dump_stream_at_ESI();
+:(code)
+void dump_stream_at_ESI() {
+  uint32_t stream_start = Reg[ESI].i;
+  int32_t stream_length = read_mem_i32(stream_start + 8);
+  dbg << "stream length: " << std::dec << stream_length << end();
+  for (int i = 0;  i < stream_length + 12;  ++i)
+    dbg << "0x" << HEXWORD << (stream_start+i) << ": " << HEXBYTE << NUM(read_mem_u8(stream_start+i)) << end();
+}
+
 //: helpers
 
 :(code)
diff --git a/subx/apps/survey.subx b/subx/apps/survey.subx
index a3e5cb5a..deedebef 100644
--- a/subx/apps/survey.subx
+++ b/subx/apps/survey.subx
@@ -1174,6 +1174,7 @@ $compute-addresses:segment-loop:
 $compute-addresses:segment-break:
     # ESI = labels
     8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           6/r32/ESI   0xc/disp8       .                 # copy *(EBP+12) to ESI
+#? $dump-stream-at-ESI:
     # lrow/EAX = labels->data
     8d/copy-address                 1/mod/*+disp8   6/rm32/ESI    .           .             .           0/r32/EAX   0xc/disp8       .                 # copy ESI+12 to EAX
     # max/ECX = labels->data + labels->write
@@ -1182,9 +1183,61 @@ $compute-addresses:segment-break:
 $compute-addresses:label-loop:
     # if (lrow >= max) break
     39/compare                      3/mod/direct    0/rm32/EAX    .           .             .           1/r32/ECX   .               .                 # compare EAX with ECX
-    73/jump-if-greater-or-equal-unsigned  $compute-addresses:end/disp8
+    0f 83/jump-if-greater-or-equal-unsigned  $compute-addresses:end/disp32
+    # dump lrow->key {{{
+    # . write(2/stderr, "label: ")
+    # . . push args
+    68/push  "label: "/imm32
+    68/push  2/imm32/stderr
+    # . . call
+    e8/call  write/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
+    # . write(2/stderr, lrow->key)
+    # . . push args
+    ff          6/subop/push        0/mod/indirect  0/rm32/EAX    .           .             .           .           .               .                 # push *EAX
+    68/push  2/imm32/stderr
+    # . . call
+    e8/call  write/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
+    # . write(2/stderr, "$\n")
+    # . . push args
+    68/push  "$\n"/imm32
+    68/push  2/imm32/stderr
+    # . . call
+    e8/call  write/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
+    # }}}
     # seg-name/EDX = lrow->segment-name
     8b/copy                         1/mod/*+disp8   0/rm32/EAX    .           .             .           2/r32/EDX   4/disp8         .                 # copy *EAX to EDX
+    # dump seg-name {{{
+    # . write(2/stderr, "compute-addresses: seg-name: ")
+    # . . push args
+    68/push  "seg-name: "/imm32
+    68/push  2/imm32/stderr
+    # . . call
+    e8/call  write/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
+    # . write(2/stderr, seg-name)
+    # . . push args
+    52/push-EDX
+    68/push  2/imm32/stderr
+    # . . call
+    e8/call  write/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
+    # . write(2/stderr, "$\n")
+    # . . push args
+    68/push  "$\n"/imm32
+    68/push  2/imm32/stderr
+    # . . call
+    e8/call  write/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
+    # }}}
     # label-seg/EDX : (address segment-info) = get(segments, seg-name, row-size=16)
     # . save EAX
     50/push-EAX
@@ -1220,7 +1273,7 @@ $compute-addresses:label-loop:
     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0x14/imm32        # add to ESP
     # lrow += 16  # size of row
     05/add-to-EAX  0x10/imm32
-    eb/jump  $compute-addresses:label-loop/disp8
+    e9/jump  $compute-addresses:label-loop/disp32
 $compute-addresses:end:
     # . restore registers
     5f/pop-to-EDI