diff --git a/317abort.subx b/317abort.subx
index 8c6b3b48..3a2aad43 100644
--- a/317abort.subx
+++ b/317abort.subx
@@ -15,13 +15,24 @@ abort:  # e: (addr array byte)
       eb/jump loop/disp8
     }
 
+# destroys the heap
 dump-call-stack:
     # . prologue
     55/push-ebp
     89/<- %ebp 4/r32/esp
     # . save registers
     50/push-eax
+    51/push-ecx
+    52/push-edx
     53/push-ebx
+    # var labels/edx: (stream {label-name, address} 0x1000)
+    81 5/subop/subtract %esp 0xc000/imm32
+    68/push  0xc000/imm32
+    68/push  0/imm32/read
+    68/push  0/imm32/write
+    89/<- %edx 4/r32/esp
+    #
+    (load-debug-symbols %edx)  # destroys the heap
     # traverse the linked list of ebp pointers: https://wiki.osdev.org/Stack_Trace
     8b/-> *ebp 3/r32/ebx
     {
@@ -37,8 +48,55 @@ dump-call-stack:
       e9/jump loop/disp32
     }
 $dump-call-stack:end:
+    # . reclaim locals
+    81 0/subop/add %esp 0x100c/imm32
     # . restore registers
     5b/pop-to-ebx
+    5a/pop-to-edx
+    59/pop-to-ecx
+    58/pop-to-eax
+    # . epilogue
+    89/<- %esp 5/r32/ebp
+    5d/pop-to-ebp
+    c3/return
+
+load-debug-symbols:  # labels/edx: (stream {label-name, address})
+    # . prologue
+    55/push-ebp
+    89/<- %ebp 4/r32/esp
+    # . save registers
+    50/push-eax
+    51/push-ecx
+    52/push-edx
+    53/push-ebx
+    # create space for a stream on the heap, clobbering any existing data
+    # var ecx: (addr stream byte)
+    b9/copy-to-ecx 0x03000000/imm32
+    c7 0/subop/copy *ecx 0/imm32  # write index
+    c7 0/subop/copy *(ecx+4) 0/imm32  # read index
+    c7 0/subop/copy *(ecx+8) 0x01000000/imm32  # stream capacity = 16MB
+    # load 0x100 sectors starting from sector 10080 = 0x2760
+    (load-sectors Primary-bus-primary-drive 0x2760 0x100 %ecx)
+    b8/copy-to-eax 0x0300000c/imm32
+    b9/copy-to-ecx 0/imm32
+    {
+      3d/compare-eax-and 0x030000ff/imm32
+      74/jump-if-= break/disp8
+      #
+      8a/byte-> *eax 1/r32/CL
+      (draw-grapheme-at-cursor 0 %ecx 7 0)
+      (move-cursor-rightward-and-downward 0)
+      #
+      40/increment-eax
+      eb/jump loop/disp8
+    }
+$load-debug-symbols:end:
+    # . reclaim locals
+    81 0/subop/add %esp 0x100c/imm32
+    # . restore registers
+    5b/pop-to-ebx
+    5a/pop-to-edx
+    59/pop-to-ecx
     58/pop-to-eax
     # . epilogue
     89/<- %esp 5/r32/ebp
diff --git a/boot.subx b/boot.subx
index 7ded7309..afe826ca 100644
--- a/boot.subx
+++ b/boot.subx
@@ -889,12 +889,33 @@ Font:
 
 == data
 
-# We'll be gaining access just to the secondary drive on the primary bus for
-# now. It will have the designated 'data' disk so we don't mess with the code
-# disk.
-#
-# The type definition for this variable is in safe Mu (rather than unsafe
-# SubX) code.
+# code disk
+# All ports are 8-bit except data-port, which is 16-bit.
+Primary-bus-primary-drive:
+  # command-port: int (write)
+  0x1f7/imm32
+  # status-port: int (read)
+  0x1f7/imm32
+  # alternative-status-port: int (read)
+  0x3f6/imm32
+  # error-port: int (read)
+  0x1f1/imm32
+  # drive-and-head-port: int
+  0x1f6/imm32
+  # sector-count-port: int
+  0x1f2/imm32
+  # lba-low-port: int
+  0x1f3/imm32
+  # lba-mid-port: int
+  0x1f4/imm32
+  # lba-high-port: int
+  0x1f5/imm32
+  # data-port: int
+  0x1f0/imm32
+  # drive-code: byte                # only drive-specific field
+  0xe0/imm32  # LBA mode also enabled
+
+# data disk
 # All ports are 8-bit except data-port, which is 16-bit.
 Primary-bus-secondary-drive:
   # command-port: int (write)
@@ -944,6 +965,7 @@ load-sectors:  # disk: (addr disk), lba: int, n: int, out: (addr stream byte)
   {
     # poll for results
 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "waiting for sector.." 7 0)
+#?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "." 7 0)
     (while-ata-busy *(ebp+8))
     (until-ata-data-available *(ebp+8))
 #?     (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "reading\n" 7 0)
diff --git a/ex2.mu b/ex2.mu
index cd170aa7..148b424e 100644
--- a/ex2.mu
+++ b/ex2.mu
@@ -25,4 +25,13 @@ fn main screen: (addr screen), keyboard: (addr keyboard), data-disk: (addr disk)
     y <- increment
     loop
   }
+  foo
+}
+
+fn foo {
+  bar
+}
+
+fn bar {
+  abort "aaa"
 }
diff --git a/translate_subx b/translate_subx
index 66df2a91..8d97b197 100755
--- a/translate_subx
+++ b/translate_subx
@@ -42,9 +42,15 @@ then
 fi
 
 # Latter half of disk is for debug info.
-dd if=labels of=code.img seek=10080 conv=notrunc
+dd if=labels of=code.img seek=10080 conv=notrunc  # keep this sync'd with abort.subx
 if [ `stat --printf="%s" labels` -ge 131072 ]  # 256 sectors * 512 bytes per sector, the most an ATA drive can read in a single command
 then
   echo "labels won't all be loaded on abort"
   exit 1
 fi
+
+if [ `wc -l < labels` -gt 4096 ]  # 0x1000 stream capacity in abort.subx
+then
+  echo "abort will go into infinite regress"
+  exit 1
+fi
diff --git a/translate_subx_emulated b/translate_subx_emulated
index aef29801..439befcd 100755
--- a/translate_subx_emulated
+++ b/translate_subx_emulated
@@ -46,9 +46,15 @@ then
 fi
 
 # Latter half of disk is for debug info.
-dd if=labels of=code.img seek=10080 conv=notrunc
+dd if=labels of=code.img seek=10080 conv=notrunc  # keep this sync'd with abort.subx
 if [ `stat --printf="%s" labels` -ge 131072 ]  # 256 sectors * 512 bytes per sector, the most an ATA drive can read in a single command
 then
   echo "labels won't all be loaded on abort"
   exit 1
 fi
+
+if [ `wc -l < labels` -gt 4096 ]  # 0x1000 stream capacity in abort.subx
+then
+  echo "abort will go into infinite regress"
+  exit 1
+fi