Using eventprocs as hooks

reyalp

14079

« on: 26 / September / 2010, 01:18:18 »

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A while back, I noticed a number of the PT_* eventprocx just point at a

Code: [Select]

MOV     R0, #0
BX      LR

It turns out that some of these are called by the camera at various points in execution. On D10, sub_FF85E9A0 checks a variable, and if set, calls ExecuteEventProcedure with a lookup into the first 12 PT_* functions.

The variable is set by SS.Create, which also registers the functions.

Theory: we call SS.Create, register our own function to replace the original that is just a return zero, we have a hook without copying a bunch of code.

Practice:

Code: [Select]

int my_PT_CompletePreCapt() {
	_LogPrintf(0x120,"my_PT_CompletePreCapt");
	return 0;
}

int my_PT_ShootPicture() {
	_LogPrintf(0x120,"my_PT_ShootPicture");
	return 0;
}

int register_pt_hooks() {
	if(_ExecuteEventProcedure("System.Create") == -1) {
		return -1;
	}
	if(_ExecuteEventProcedure("SS.Create") == -1) {
		return -1;
	}
	if(_ExecuteEventProcedure("ExportToEventProcedure","PT_CompletePreCapt",my_PT_CompletePreCapt) == -1) {
		return -1;
	}
	if(_ExecuteEventProcedure("ExportToEventProcedure","PT_ShootPicture",my_PT_ShootPicture) == -1) {
		return -1;
	}
	return 0;
}

log:

Code: [Select]

00011670: PT_CompletePreCapt
00011670: SS:my_PT_CompletePreCapt
...
00011690: UI:MuteOnPhysicalScreen
00011690: SS:Shoot
00011690: PT_ShootPicture
00011690: SS:my_PT_ShootPicture

Canon "hook" event procs:
"PT_CompletePreCapt"
"PT_RecreviewAvailable"
"PT_NextShootAvailable"
"PT_CompleteStopZoom"
"PT_CompleteStopDigZoom"
"PT_CompleteStoreLens"
"PT_MovieRecordStopped"
"PT_CompleteCaptModeChange"
"PT_CompleteSynchroWrite"
"PT_CompleteCharge"
"PT_CompleteFileWrite"
"PT_ShootPicture"

edit:
This system also exists in vxworks. The list of functions is slightly different on a540, but it looks very similar.

edit #2:
Moving shooting_expo_param_override to my_PT_CompletePreCapt does Tv override correctly on d10, for non-quickpress.

« Last Edit: 26 / September / 2010, 16:53:08 by reyalp »

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Microfunguy

4037

Re: Using eventprocs as hooks

« Reply #1 on: 26 / September / 2010, 06:57:06 »

Interesting stuff !

What do you think 'PT' stands for ?

While you are looking at this stuff, do you know if the movie-capture task can be paused anywhere without causing a crash ?

(I can start a new thread about this).

If not, is there anywhere an led can be very briefly flashed at the instant each frame is captured ?

The idea is to try to synchronise stereo movie recording in the same way we can synchronise image capture.

I did play with this some time ago but the camera always crashed.

EWAVR claimed the movie recording task could be paused but never provided details when asked.

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dvip

451

Re: Using eventprocs as hooks

« Reply #2 on: 26 / September / 2010, 11:20:21 »

This is very interesting but it's still a mystery for many.
It would be nice to have some Lua examples on how to call/use some of these EventProcedure.
It is nice to know they are there and thanks for bringing them up!

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fudgey

1705
a570is

Re: Using eventprocs as hooks

« Reply #3 on: 26 / September / 2010, 14:39:20 »

This is quite a bit more elegant than cut & pasted disassembly

For capt_seq, we still need all the asm for the raw hook, though? This makes me wonder if there are more such vacant eventprocs for testing or debug? Maybe some that aren't even empty like these PT* functions but contain things like console logging that doesn't really need to be done by a replacement...

Did we previously have a way to tell when the fw has finished charging the flash (assuming that's when PT_CompleteCharge gets called)?

For a570 list of empty PT_* eventprocs is
PT_CompletePreCapt
PT_RecreviewAvailable
PT_NextShootAvailable
PT_CompleteStopZoom
PT_CompleteStopDigZoom
PT_CompleteStoreLens
PT_CompletePrepareLens
PT_MovieRecordStopped
PT_CompleteCaptModeChange
PT_CompleteSynchroWrite
PT_CompleteCharge
edit: these are empty as well:
PT_BatLvChange_PreWeak
PT_BatLvChange_Weak
PT_BatLvChange_Low
PT_BatLvChange_SysLow

Microfunguy:
PT==ProductionTest?

dvip:
For Lua examples on event procedure calls, search the forum for "call_event_proc" (optionally by user reyalp) or see
http://chdk.setepontos.com/index.php/topic,5295.msg54097.html#msg54097
(actually, the first version is a better example for eventproc stuff since it also had an eventproc call with a pointer argument that needs a malloc: http://chdk.setepontos.com/index.php/topic,5295.msg54076.html#msg54076). Note that to experiment with eventprocs you typically need to study the disassembly first to find out what it if anything it expects as arguments and to figure out how to get it registered if it isn't registered by default.

« Last Edit: 26 / September / 2010, 15:12:34 by fudgey »

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reyalp

14079

Re: Using eventprocs as hooks

« Reply #4 on: 26 / September / 2010, 16:26:57 »

Quote from: Microfunguy on 26 / September / 2010, 06:57:06

What do you think 'PT' stands for ?

I'd say Product Test, since a540 has a function "RegisterProductTestEvent"

Quote

While you are looking at this stuff, do you know if the movie-capture task can be paused anywhere without causing a crash ?

(I can start a new thread about this).

Probably better in a new thread (or the previous one we talked about this in). I don't know myself.

Quote

If not, is there anywhere an led can be very briefly flashed at the instant each frame is captured ?

This seems like it ought to be possible, but again, I don't know anything specific.

Quote from: fudgey on 26 / September / 2010, 14:39:20

For capt_seq, we still need all the asm for the raw hook, though?

Yes, unfortunately it seems so.

Quote

This makes me wonder if there are more such vacant eventprocs for testing or debug?

Worth looking for. One way to do this is to work backwards from calls to ExecuteEventProcedure. The thing you need to do is find was that are called automatically in operation. I believe a lot of the eventprocs just exist to be called from cbasic or development or service code. In many cases the normal camera code calls the C function directly instead of going through event proc interface. So replacing Fopen_Fut doesn't let you hook everywhere the camera opens a file.

Quote

Maybe some that aren't even empty like these PT* functions but contain things like console logging that doesn't really need to be done by a replacement...

Another approach would be to figure out how to find the address of a currently registered eventproc, then you could would truly 'hook' it instead of replacing. I haven't seen an obvious way to do this, but event procs seem to be handled by something called "nameservice". It should be possible to get the proper lookup code from ExecuteEventProcedure, but it looks like it would have to be found manually or done with sigs.

There is also CreateProxyOfEventProcedure and DeleteProxyOfEventProcedure which sound interesting but I don't understand what they do.

Quote

edit: these are empty as well:
PT_BatLvChange_PreWeak
PT_BatLvChange_Weak
PT_BatLvChange_Low
PT_BatLvChange_SysLow

Are they called by the camera in normal operation ? From a quick look on a540, it appears they would be called from PT_BatTestTask.

To find ones that can be used in hooks, you need to look find ones that are called automatically. In a570, the function that "dispatches" the PT_ hooks is sub_FFEB5A60, and it only looks at the first 10. Looking for similar functions might be productive.

There is another interesting set of event procs that look like they might do something like this. On a570 100e, sub_FFC04BE0 loads an event proc name from 0xD970 and executes it. There are a bunch of similar ones that use offsets from this address. These functions (sub_FFC04BE0 etc) are themselves in a table in that gets copied to camera RAM, starting at FFF2D72C. On a540, the contents of the corresponding address (0xD310) seems to be null by default.

Edit: these are somehow used by CreateProxyOfEventProcedure and DeleteProxyOfEventProcedure

One thing that should help hunting these is that whenever an eventproc is called, the name is sent to the camera log. Of course, there may be other pre-conditions that need to be present before they are called at all (like the variable set by SS.Create in D10)

edit:
Two more likely candidates on d10, not on older cameras like a570
UIFS_ChangeShootState called by sub_FF9317E4
UIFS_ShootSeqToUI called by sub_FF931808. This one looks interesting, it is called from PostEventShootSeqToUI. Calls to this go into the camera log as "ShootSeqToUI:0x%04x:adr:%p,Para:%ld"

« Last Edit: 27 / September / 2010, 01:28:39 by reyalp »

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reyalp

14079

Re: Using eventprocs as hooks

« Reply #5 on: 26 / September / 2010, 16:57:43 »

Quote from: dvip on 26 / September / 2010, 11:20:21

This is very interesting but it's still a mystery for many.
It would be nice to have some Lua examples on how to call/use some of these EventProcedure.
It is nice to know they are there and thanks for bringing them up!

This isn't something you can use from lua. Instead, it lets us make C code that is automatically called from canon firmware (without copying all the asm up to where they need to be called). The lua system would need quite a bit of hacking to allow us to implement these hooks in lua.

I wonder if a cbasic sub will be called ?

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dvip

451

Re: Using eventprocs as hooks

« Reply #6 on: 27 / September / 2010, 10:38:01 »

Thanks for the clarification reyalp.

I was ready to call _ExecuteEventProcedure("ExportToEventProcedure","PT_ShootPicture",my_PT_ShootPicture)

and use pointers from Lua

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fudgey

1705
a570is

Re: Using eventprocs as hooks

« Reply #7 on: 27 / September / 2010, 15:53:09 »

Quote from: reyalp on 26 / September / 2010, 16:26:57

Two more likely candidates on d10, not on older cameras like a570
UIFS_ChangeShootState called by sub_FF9317E4
UIFS_ShootSeqToUI called by sub_FF931808. This one looks interesting, it is called from PostEventShootSeqToUI. Calls to this go into the camera log as "ShootSeqToUI:0x%04x:adr:%p,Para:%ld"

Things like
00040800: ShootState:0x4
00040870: ShootSeqToUI:0x2001:adr:0xffd5db18,Para:-2761960
do get written to a570 romlog a lot, though...

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reyalp

14079

Re: Using eventprocs as hooks

« Reply #8 on: 13 / October / 2012, 23:43:56 »

Some further investigation. On A540, the function that calls these is sub_FFD4F7F0, (which I've named call_PT_hook)

There are 10 hooks available on A540, as seen by the check in this function. Prior to calling call_PT_hook, the Canon firmware frequently calls sub_FFD41024, which in turn calls PostEventShootSeqToUI. The event numbers are noted below.

Num	Name	Called at	Event
0	PT_CompletePreCapt	FFD421D0	0x2006
1	PT_RecreviewAvailable	FFD4223C	0x2008
2	PT_NextShootAvailable	FFD42220	0x2007
3	PT_CompleteStopZoom	FFD41728	0x200b, 0x200d, 0x200c
4	PT_CompleteStopDigZoom	FFD41880	0x200e, 0x2010, 0x200f
5	PT_CompleteStoreLens	FFD414A8	0x2004
6	PT_CompletePrepareLens	?	-
7	PT_MovieRecordStopped	FFD424E0	0x200a
8	PT_CompleteCaptModeChange	FFD41A3C **	-
9	PT_CompleteSynchroWrite	?	-
10	PT_CompleteCharge	FFD41058	0x2001

* called conditionally
** immediately followed by ref to log string "SS:CompleteCaptureModeChange"

« Last Edit: 14 / October / 2012, 00:11:50 by reyalp »

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reyalp

14079

Re: Using eventprocs as hooks

« Reply #9 on: 14 / October / 2012, 00:11:33 »

D10
call_PT_hook = sub_FF85E9A0, total hooks = 11 event func sub_FF826754
Note that unlike a540, PT_CompletePrepareLens is not present, while PT_CompleteFileWrite and PT_ShootPicture are added. Where defined, the event numbers seem to match.

Num	Name	Called at	Event
0	PT_CompletePreCapt	FF8249D0	0x2006
1	PT_RecreviewAvailable	FF824A10	0x2008
2	PT_NextShootAvailable	FF8249F4	0x2007
3	PT_CompleteStopZoom	FF8248A4	0x200b, 0x200d, 0x200c
4	PT_CompleteStopDigZoom	FF824914	0x200e, 0x2010, 0x200f
5	PT_CompleteStoreLens	FF824834	0x2004
6	PT_MovieRecordStopped	FF824AB0	0x200a
7	PT_CompleteCaptModeChange	FF8252F4 **	-
8	PT_CompleteSynchroWrite	?	-
9	PT_CompleteCharge	FF824794	0x2001
10	PT_CompleteFileWrite	FF90D488	-
11	PT_ShootPicture	FF825EDC ***	-

* called conditionally
** immediately followed by log string "ModChg*"
*** preceded by log string "Shoot"

edit:
As noted earlier

Quote

UIFS_ShootSeqToUI called by sub_FF931808. This one looks interesting, it is called from PostEventShootSeqToUI. Calls to this go into the camera log as "ShootSeqToUI:0x%04x:adr:%p,Para:%ld"

This looks like it can be used to hook all events posted with PostEventShootSeqToUI. It is registered by UI_Create which also sets a flag at 0x6208 to 1, which allows the hook to be called. The same function registers all named levents as eventprocs, which probably consumes a significant amount of memory.

« Last Edit: 14 / October / 2012, 00:34:40 by reyalp »

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