geckoloader / Loading and run the stub

Hello everyone,

I'm currently examining the source of geckoloader. (I want to learn how create a stub and a loader.)

So I examined the stub code and quickly the loader code.
All this code make sense for me

However regarding the boot code, I see these global variables at the beginning of the code :

extern u8 stub_bin[];
extern u32 stub_bin_size;
extern u8 loader_dol[];
extern u32 loader_dol_size;

But, I did not find where are defined these variables on the other source files.

In fact, I want to know how to load the stub code in the stub_bin[] array.
Because I have a stub.dol but this is a file, this is not in memory.

I assume that there's a way to push the stub code in a special section of the dol file.

How to do it ? And then how to use it ?

Could someone give me some clues ?

I hope that my question is making sense.
Maybe I'm totally wrong, (programming is just a hobby for me).

Regards,
ShovAge

Please ignore my poor english.

The stub and loader parts get compiled to .elf and objdump is used to extract the blobs to .bin. The toplevel Makefile then uses bin2s to make a compilable .S out of the .bins. Those get compiled by the boot part, it's just a way to include the blob in the resulting geckoloader.elf.

The externs you mentioned are in those .S files.

Thanks a lot for your help.
Your answer really helps.

If I'm right, the executable sections from stub and loader are extracted to a bin file.
Then this bin file is converted to an ASM source file.
Then these files are compiled in the same time than geckoloader and included in geckoloder.elf
That's it ?

I tried objdump on my linux box.
It seems that the original objdump is only used for the IA32 architecture.

So, I found the executable powerpc-gekko-objdump.
I do not really know how to use it.

I tried it:
powerpc-gekko-objdump --target=binary -d geckoloader.elf

I used -d because we have the following description in the help page:
-d, --disassemble Display assembler contents of executable sections

I assume that we have to set an architecture. The command give me these choices:
supported architectures: rs6000:6000 rs6000:rs1 rs6000:rsc rs6000:rs2 powerpc:common powerpc:common64 powerpc:603 powerpc:EC603e powerpc:604 powerpc:403 powerpc:601 powerpc:620 powerpc:630 powerpc:a35 powerpc:rs64ii powerpc:rs64iii powerpc:7400 powerpc:e500 powerpc:e500mc powerpc:MPC8XX powerpc:750

I did not suceed to extract the executable section. :/

And, I had a look on Makefiles to see when objdump is used without success.
Where can I found the comands on the Makefiles ?
And, withotu the Makefiles, how can I manually extract executable section and compile an other program with included .S files ?

Thanks again.

Rgds,
ShovAge

Uh-oh, my bad, its objcopy not objdump. For this toolchain you use powerpc-gekko-objcopy with the arguments "-O binary ", see stub/Makefile.
bin2s is included in devkitPPC, thats the tool you want to use to turn blobs into a .S to integrate it into another project.

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Great !
That's working !

Happy to play with this new tool ! :)

Thanks for your help !