Questions on first PSP Program.

[StorMyu]

Hi !

I had an idea about making an Eboot swaper using a plugin and swapping on the fly an Eboot loaded in memory at a start of a game, but I've never really programmed for PSP and I just have some questions about it.

as said here by Codestation:
http://wololo.net/talk/viewtopic.php?f=13&t=9276&start=210#p120961

That's what he used to Swap module in his ZeroVSH plugin.
using:
SceModule * sceKernelFindModuleByName(const char *modname);

Here's the questions:

- How the plugins are working ? (in general, I mean there's no execution whatsoever)
- I know the rules are not "do not ask anyone to program for you" so, it's just related to the first question, how could I hook all modules launched ? (like locating every .prx launched in memory to write them in a .txt file for example)
- what are Kernel mode / user mode ? what's the main difference to take into account while programming ?

And probably some others but I'll stop at those for the moment.

by the way, the Eboot swap could be used for translation purpose (like codestation did on Project Diva but not changing just sentences but the whole Eboot from the memory stick), to be able to play UMD with some translations.

Thanks for the future answer.

[Xian Nox]

What you are trying to do is far more advanced than your knowledge on the matter. Please learn PC programming first, then move to PSP.

[StorMyu]

That still doesn't answer the questions...
And I don't see how my knowledge is relevant here, I'm only asking for some informations.
I was just explaining what I wanted to do to give a general idea.

Edit: don't take it bad heh

[Xian Nox]

- How the plugins are working ? (in general, I mean there's no execution whatsoever)

Plugins are dynamically loadable/unloadable application modules. They are loaded when needed, and are nothing more than blocks of code. And what do you mean, "there's no execution whatsoever"?

- I know the rules are not "do not ask anyone to program for you" so, it's just related to the first question, how could I hook all modules launched ? (like locating every .prx launched in memory to write them in a .txt file for example)

Different ways. You can find a function's address and overwrite it with your own, or add a jump instruction at its beginning, or you can hook them up in a way similar to that of HBL. This way you can overwrite the one that loads modules, and make it load custom ones instead.

- what are Kernel mode / user mode ? what's the main difference to take into account while programming ?

Kernel mode generally refers to the memory space reserved for the operating system. Similarly, user mode refers to the one for all user applications and their data. Kernel mode applications have more privileges than user-mode applications, and depending on the platform (incl. PSP), may be protected from modification.

[StorMyu]

Plugins are dynamically loadable/unloadable application modules. They are loaded when needed, and are nothing more than blocks of code. And what do you mean, "there's no execution whatsoever"?

I meant how the plugin will activate or mostly when, because I want the plugin to use my function anytime a module (a prx) is loaded, that's why I was asking about the "execution".
That's probably my main question here... to replace the Eboot.bin from another one in the memory stick when it's loaded.

Thanks for the answers btw.

[NightStar3]

Plugins are dynamically loadable/unloadable application modules. They are loaded when needed, and are nothing more than blocks of code. And what do you mean, "there's no execution whatsoever"?

I meant how the plugin will activate or mostly when, because I want the plugin to use my function anytime a module (a prx) is loaded, that's why I was asking about the "execution".
That's probably my main question here... to replace the Eboot.bin from another one in the memory stick when it's loaded.

Thanks for the answers btw.

If you want to redirect files -> hook a driver's (depending on where the file resides) IoOpen function.
Also, if you want to dump a .prx's data to a text file -> patch ProbeExec, dump the data to a local buffer, and write it to the text file.

Hope that helped,
NightStar3

EDIT: If you want to load your function right before a prx is loaded -> patch IoOpen (depending on the driver the module is being loaded from)
Then, you can do checks to see if the module is being passed to IoOpen, and load your function right before it (and pass normal IoOpen to return)

[m0skit0]

- How the plugins are working ? (in general, I mean there's no execution whatsoever)

VSH/game plugins are kernel modules that are loaded before VSH/game is loaded. And they're executed, indeed.

how could I hook all modules launched ? (like locating every .prx launched in memory to write them in a .txt file for example)

You would need to hook sceKernelLoadModule() at kernel level.

what are Kernel mode / user mode ? what's the main difference to take into account while programming ?

Look MIPS documentation for this. Resuming: kernel mode is like God mode, where you can access anything accessable by software on the PSP. User mode is a restricted mode where games and VSH (basically anything not the kernel) is running (thus limited memory and hardware access).

I meant how the plugin will activate or mostly when

At kernel reset and after all kernel modules (btcnf) are loaded. Check PRO CFW source code for more detailed information.