ELF section hacking!

Makefile

all: section_hacking

section_hacking:
	gcc -g -O0 -Werror -Wall -o section_hacking section_hacking.c plugin.c

clean:
	rm -f *.o section_hacking

output.txt

Formatters are sitting from 0x0x601020 to 0x0x601060
Formatting with in_quotes: "My Formatted Text"
Formatting with in_equotes: `My Formatted Text'
Formatting with in_arrows: hi-->>>My Formatted Text<<<---
Formatting with in_pizza: :pizza:My Formatted Text:pizza:

plugin.c

#include <stdio.h>
#include "section_hacking.h"

static void in_equotes(const char *txt)
{
    printf("`%s'\n", txt);
}
REGISTER_FORMATTER(in_equotes);

static void in_arrows(const char *txt)
{
    printf("-->>>%s<<<---\n", txt);
}
REGISTER_FORMATTER(in_arrows);

static void in_pizza(const char *txt)
{
    printf(":pizza:%s:pizza:\n", txt);
}
REGISTER_FORMATTER(in_pizza);

section_hacking.c

#include <stdio.h>
#include "section_hacking.h"

static void in_quotes(const char *txt)
{
    printf("\"%s\"\n", txt);
}
REGISTER_FORMATTER(in_quotes);

extern struct formatter_info __start_my_formatters;
extern struct formatter_info __stop_my_formatters;

static void format_all(const char *txt)
{
    struct formatter_info *iter = &__start_my_formatters;

    for ( ; iter < &__stop_my_formatters; ++iter) {
	printf("Formatting with %s: ", iter->name);
	iter->fn(txt);
    }
}

int main(int argc, char *argv[])
{
    printf("Formatters are sitting from 0x%p to 0x%p\n",
	   (void *)&__start_my_formatters,
	   (void *)&__stop_my_formatters);

    format_all("My Formatted Text");

    return 0;
}

section_hacking.h

#ifndef __SECTION_HACKING_H__
#define __SECTION_HACKING_H__

typedef void (*formatter_fn_t)(const char *);

struct formatter_info {
    formatter_fn_t fn;
    char *name;
};

#define REGISTER_FORMATTER(func)			\
    static struct formatter_info __formatter_ ## func	\
    __attribute((__section__("my_formatters")))		\
    __attribute((__used__)) = {				\
	.fn = func,					\
	.name = #func,					\
    }

#endif /* __SECTION_HACKING_H__ */