forums.ps2dev.org

[serige]

Hi everyone,

I am finally free from school again and able to learn more about my PSP :)

After playing around with the internal memory for a few days, I found out the following main memory layout for a typical application at its run time (I assume it is also true for many other apps):

************************************************
(higher address)
------stack (local data for procedures)
|
| (going down)
V


^
| (going up)
|
-------- dynamic data segment (allocate at run time)
|
static data segment (allocated at compile time)
|
---------
|
text segment (program executable)
|
--------- 0x4000
??? (reserved segment maybe)
--------- 0x0
(lower address)
************************************************

A blur line for me at the moment is the line which separates the static data segment and the starting address of the dynamic data segment. I am assuming there is a pointer somewhere pointing to this boundary (or a variable specifies the size of the static data segment), but I haven't fount it yet. Maybe someone can direct me to a source discussing about the boot header format (for pre-3.xx fw, which is what I am working with).

Anyway, I am hoping to learn more about this this summer. So, I am thinking whether or not I am able to shift the static data segment up a little bit. My goal is to insert a small amount of data at the bottom of the static data segment, and therefore "lifting" up the whole segment by a small offset, while the application still runs as if the segment has not been changed. Now, I know there are going to be pointers in the text segment pointing at the the data in the static data segment, the question is whether or not I can go in and change all these pointers and make them pointing at the right places. Is this possible though, to literally trace all of the static data pointers? Besides what I've mentioned above, is there any other places I need to look at in order to make sure the app run healthy?

I know there is a heavy assembly involved, but I want to do it as a summer project. Thanks for helping me :)

[crazyc]

What exactly do you want to do? All the addresses (in the rodata, data and bss segments) within the executable are resolved at link time. To move any of them at run time would require you to fix up the offsets within the whole program and fix the relocations. You could, I suppose, if you know the start address of the part you want to move, you could copy the part to the new location then use the relocation addresses to fix everything up, but there might be a easier way to accomplish whatever it is you are trying to do.

PS. The _fdata symbol points to the start of the read write data segment and _fbss points to the start of the uninitialized data segment.

[serige]

[jimparis]

Just change it at link time, do you really need to do it at runtime?
You should be able to set things up however you'd like by modifying the linker script accordingly.

[serige]

[J.F.]

Given what you are trying to do, asking for help is self-defeating. If you don't know how, go learn. We don't give lessons here in any case. This is a developer board, not a correspondence class for ITT.

[serige]

[J.F.]

[serige]

[crazyc]

[serige]

[TyRaNiD]

So what you want is to be able to step through code at the instruction level then? Well... for a start GDB does that, psplink should do that (not checked it still works :P). Alternatively use printf perhaps, if you run your code in psplink then doing printf (or fprintf(stderr, ...)) will spit out to your local terminal.

Of course I am not necessarily saying you have to use psplink but you are not making much sense really, and it sounds like psplink already does what you want and is freely available with source for people to look at (and no doubt steal as per)

If that is not what you want to do, I have no idea what it is :P

[serige]