Putting code and data into the same section in a Linux kernel module

Question

I'm writing a Linux kernel module in which I would like to have some code and associated data in the same section. I declare the data and the functions with the attribute tags, like:

void * foo __attribute__ ((section ("SEC_A"))) = NULL;
void bar(void)  __attribute__ ((section("SEC_A")));

However when I do this, gcc complains with:

error: foo causes a section type conflict

If I do not declare the function with the specific section name, gcc is fine with it. But I want both the function and the variable to be in the same section.

Is there any way to do that with gcc? My gcc version is gcc (Ubuntu 4.3.2-1ubuntu12) 4.3.2

Answer 1

From the GCC manual:

Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

IIRC, linux uses a flat memory model, so you don't gain anything by "forcing" things into a single section, anyway, do you?

Hmmm. I suppose you could make an asm function to reserve the space and then do pointer foo to get it's address. Might want to wrap the ugly in a macro...

Another thought would be to split the problem in half; write a small example case of the closest thing you can and still compile, get the asm code, and tinker with it to see what you can get past the downstream stages. If nothing else, you could write something to mungle the asm code for that module, entomb it in you make file, and call it good.

Yet another thought: try putting the variable definitions in a small asm module (e,g, as db's or whatever with the right section declarations) and let the linker handle it.

Answer 2

I think you cannot put text (function) and data (BSS) objects into the same section because (some) OSes assume immutability of .TEXT section types for process re-use.