tools/loading_tip_patcher/TRACE.md

Dynamic trace for the loading-tip cycle function

The static RE pass narrowed the candidate function to a small set of VMAs in 0x141174xxx (loading-screen construction) and a few call targets. To confirm which one is the per-frame tip cycler, we use hardware breakpoints to observe the running eu4.exe.

Why

Manual RE of a 38 MB binary without symbols is slow. The cycle function is not the 0x141174F50 setup function (which runs only once). The per-frame update is somewhere else, calling the same findChildByName / setText virtuals, but with a Timer. Hardware breakpoints on the candidates and a hit counter tell us which one fires most often during the loading screen.

Tool

bin/trace_tip_cycle.exe (built with x86_64-w64-mingw32-gcc, MinGW-w64 GCC 15.2.0). It:

1. Finds the eu4.exe PID.
2. Opens the main thread.
3. Sets DR0–DR3 hardware-execute breakpoints on the first 4 candidate VMAs.
4. Calls DebugActiveProcess to attach as a debugger.
5. Loops on WaitForDebugEvent, logs every EXCEPTION_SINGLE_STEP whose ExceptionAddress matches a candidate, and re-arms all 4 breakpoints (Windows clears them on exception).
6. Exits after 10000 hits or 5 minutes, whichever comes first.

The hit log is written to trace_log.txt next to the .exe.

Candidates currently traced

VMA	Source
0x141174F50	load_screen_setup (static RE confirmed, runs once)
0x141174840	status_updater (spinner — confirmed fires every frame)
0x141175110	status_lookup (helper, may or may not be per-frame)
0x14117AD80	call target — likely the GUI addChild path
(12 more)	See src/trace_tip_cycle.cpp for the full list

Only the first 4 fit in the 4 HW debug registers. If the cycle function is one of the others, expand the candidate list and re-build.

How to run

1. Launch EU4 through Steam. (Or directly: "C:\Program Files (x86)\Steam\steamapps\common\Europa Universalis IV\eu4.exe".)
2. Trigger a loading screen — start a new campaign, or load a save. The loading screen must be on-screen for the tip cycler to run.
3. In a second shell, run the tracer:

   cd tools/loading_tip_patcher
   ./bin/trace_tip_cycle.exe
   

4. Wait 30–120 s for the loading to finish and the tracer to record enough hits.
5. Open trace_log.txt. The VMA with the highest hit count is the per-frame tip cycle function. Compare with the candidate list to identify the exact symbol we should patch.

Expected output (illustrative)

[trace] target PID 12345, main thread TID 12350
[trace] HW breakpoints set on first 4 candidates
[trace] Waiting for exceptions. Run the loading screen NOW.
[hit] #1  vma=0x141174840  count=1  prev_rip=0x141174812  +dt=12us
[hit] #1  vma=0x141174840  count=2  prev_rip=0x141174812  +dt=16543us
[hit] #1  vma=0x141174840  count=3  prev_rip=0x141174812  +dt=16601us
[hit] #0  vma=0x141174f50  count=1  prev_rip=0x141174e9f  +dt=8us
[hit] #1  vma=0x141174840  count=4  prev_rip=0x141174812  +dt=16572us
...

The expected pattern: 0x141174840 (status updater / spinner) fires 30 times per second while the loading screen is up. If a new VMA fires every few seconds (8 s interval), that is the tip cycle function.

After the trace

1. Identify the new VMA from the log.
2. Add it to the static-RE notes in RE_notes.md.
3. Add a candidates[] entry in src/trace_tip_cycle.cpp and src/main.cpp (with a TODO marker for the actual byte-pattern patch).
4. Re-run with the new candidate list if necessary.

Caveats

• DebugActiveProcess will freeze the target until the trace loop is running. If you set the breakpoint and then close the tracer, the target will be left in a frozen state. Kill eu4.exe with Task Manager to recover.
• x64 Windows only allows 4 HW execute breakpoints. The 5th and later candidates in the list will not fire. If the cycle function isn't in the first 4, you must narrow the list and re-run.
• The tracer is not stealthy — Paradox's anti-cheat (if it runs in eu4.exe) will likely detect DebugActiveProcess on the same process. Don't use this on an ironman / multiplayer session.