Built-in Module Loading

[Therx]

Is it possible to make a loop which calls every function linked into the kernel which begin "init_" I'd rather do this than have to add and remove lines as I add and remove module source files from the linker script

[Pype.Clicker]

Yes. You can for instance write down a small perl utility that would call objdump --symbols on every binary files and put calls to _init_[a-zA-Z0-9_]+ in a autoinit.c file you would generate dinamically.

It is also possible to make use of the section-selection feature of ELF files: you could then #define a small initializor(fctname) that adds the initializing info about <fctname> into a special .init section ...
(iirc, this implies the use of some asm("name"), but it's not compatible with COFF output, though

[Chris Giese]

You could use something like static C++ constructors, but in
C. GCC supports this with __attribute__((constructor)):

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int init_keyboard(void) __attribute__((constructor));
int init_keyboard(void) { /* ...whatever... */ return 0; }

int init_video(void) __attribute__((constructor));
int init_video(void) { /* ... */ return 0; }

Pointers to each 'constructor' function will be placed in
the .ctors section of the .o file. Use a linker script to
fold this section into .text, and define labels at the
start and end of the pointer array:

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    .text : {
/* ... */
   *(.text*)
   *(.rodata*)
   start_ctors = .;  _start_ctors = .;
   *(.ctor*)
   end_ctors = .;  _end_ctors = .;
    }

Now you can go through the table, calling each 'constructor'
function, from start_ctors to end_ctors. In AS:

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   mov $start_ctors,%ebx
   jmp 2f
.1:
   call *(%ebx)
   add $4,%ebx
.2:
   cmp $end_ctors,%ebx
   jb 1b

In C, maybe something like this:

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typedef int (*int_fn_void_t)(void);

extern int_fn_void_t *start_ctors, *end_ctors;

int main(void) {
   int_fn_void_t *init;

/* ... */
   for(init = start_ctors; init < end_ctors; init++)
      (*init)();
/* ... */

Turbo C does something like this, using #pragma startup

[Pype.Clicker]

hmm ... i didn't know about that "constructor" attribute ... is this something that came with last versions of GCC or is it something that was already present in 2.95.x ?

[Chris Giese]

__attribute__((constructor)) works with the two versions of GCC 2.95.2 available to me (DJGPP and MinGW).

The name of the constructor section was changed, though. Under GCC 2.95.2, it was ".ctor", now (GCC 3.2) it's ".ctors"