Compat: force zero word into sdata

[riptl]

Problem

RVL/NAND contains empty strings like strcpy(dest, "").
These strings get placed as 0x00000000 in sdata.

This is hard to reproduce from inline assembly:
All of the below allocate an sbss entry in the object file, not sdata.

char c[] = "";
__declspec(section ".sdata") u32 u = 0;
__declspec(section ".sdata") float f = 0.0f;

Task

Figure out a way how to declare a zero word in .sdata and document it.

[riptl]

@riidefi @kiwi515 do you have any ideas?

[kiwi515]

Have you tried making the data const? I think that might just put it in sbss2 though

[kiwi515]

Actually, couldn't you just recreate the strcpy call in a stripped function? If you have string pooling on the string constant will stay in the binary.

[riptl]

Thanks @kiwi515, yeah decompiling works.
Const landed in sbss2 and __declspec(section ".sdata") const char[] = ""; again landed in sbss :D a bit painful.
I was hoping we could find a solution at the inline asm level (for splitting).

[riptl]

This has been solved using the MKW_PATCH macro. It allows us to place a dummy non-zero value to force a variable into .sdata, as well as a patch instruction in a custom section.

This mechanism is fully relocatable. That way we only have to patch the final ELF before transforming into DOL.