The xserver local service is reachable from a payload, but a connect made
inside the rdebug process is accepted at the service layer and then never
dequeued: the server's accept callback runs (3F34EC50), but no 12-byte X11
setup read follows and Xlib waits in select.
create_process(entry,name,stack,1,arg) from a new process fixes it. xlaunch
creates the child; the server reads the setup (READ12 ret 0x0C), writes the
reply (8 + 0x90), and xhello creates/maps/syncs a 400x200 window. The payload
also had to keep Display* in a11 (callee-saved) instead of reloading it from a
RAM cell, and re-run SETF after each Xlib call.
Final breakpoint-free frame: dwt/gui/evidence/xhello_window_frame2838.png.
ROM untouched (b46a3e442ccb86134d2356bd70d22fd2).
Static: the VT1200 GUI is an X11 dix server in ROM plus Xlib clients
(SERVER, SESSIONMGR/Terminal Manager, WM, VTE). Internal clients use the
local service "xserver" via the display string "0::0"; TCP 6000 is a
separate authorised listener. Function table and the 4-call hello-window
sequence are in dwt/notes/GUI_APPS.md.
Dynamic: a poke+jump payload proved the firmware ABI (strlen=4) and then
called XOpenDisplay; it never returns (stage 2, display 0, X-server client
watermark unchanged) and the rdebug service dies. Verdict: hard for a
self-contained window; shared-RAM UI mutation (opcode 8) is the working
route.
SDD