section-picture.c

#include <stdint.h>

#include <stdio.h>
#define OUTPUT_SOMEWHERE(...) \
  printf(__VA_ARGS__);

typedef struct
{
  size_t something;
  size_t something_else;
  size_t third_something;
} section_array_member;

extern section_array_member __start_struct_array[] __attribute__((weak));
extern section_array_member __stop_struct_array[] __attribute__((weak));

static const section_array_member x __attribute__((used)) __attribute__((section("struct_array"), aligned(1))) =
{
  .something = 0x0000000000000000,
  .something_else = 0xffffffffffffffff,
  .third_something = 0xffffffffffffffff
};
//static int x_index = (&x - __start_struct_array);

static const section_array_member y __attribute__((used)) __attribute__((section("struct_array"), aligned(1))) =
{
  .something = 0xffffffffffffffff,
  .something_else = 0xffffffffffffffff,
  .third_something = 0xffffffffffffffff
};
//static int y_index = (&y - __start_struct_array);

static void section_function1 (const char *name);
static void (*__static_global_section_function1) (const char *)
__attribute__((used)) __attribute__((section("function_pointer_array"))) = section_function1;
static void section_function1 (const char *name) {int x = 5; OUTPUT_SOMEWHERE("%d\n", x);}

static void section_function2 (const char *name);
static void (*__static_global_section_function2) (const char *)
__attribute__((used)) __attribute__((section("function_pointer_array"))) = section_function2;
static void section_function2 (const char *name) {OUTPUT_SOMEWHERE("xyz\n");}

typedef void (*section_function_pointer)(const char *);
extern section_array_member __start_struct_array[] __attribute__((weak));
extern section_array_member __stop_struct_array[] __attribute__((weak));
extern section_function_pointer __start_function_pointer_array[] __attribute__((weak));
extern section_function_pointer __stop_function_pointer_array[] __attribute__((weak));

static void dump_memory(char *prefix, unsigned char *ptr, size_t size)
{
  size_t index;

  OUTPUT_SOMEWHERE("%s:\n", prefix);

  for (index = 0; index < size; index++) {
    OUTPUT_SOMEWHERE("%02x ", ptr[index]);
	if (!((index + 1) % 8)) {
	  OUTPUT_SOMEWHERE("| ");
	}
	if (!((index + 1) % 32)) {
	  OUTPUT_SOMEWHERE("\n");
	}
  }

  OUTPUT_SOMEWHERE("\n");
}

static int get_index(const section_array_member *member) {
  return member - __start_struct_array;
}

int
main(int argc, char **argv)
{
  OUTPUT_SOMEWHERE("*** section 'struct_array' ***\n");
  OUTPUT_SOMEWHERE("Local variables:\n");
  OUTPUT_SOMEWHERE("x_index: %d\n", get_index(&x));
  OUTPUT_SOMEWHERE("y_index: %d\n", get_index(&y));
  dump_memory("x", (unsigned char *)(&x), sizeof(section_array_member));
  dump_memory("y", (unsigned char *)(&y), sizeof(section_array_member));
  dump_memory("Section contents", (unsigned char *)__start_struct_array,
    (size_t) (((unsigned char *)__stop_struct_array) - ((unsigned char *)__start_struct_array)));

  OUTPUT_SOMEWHERE("*** section 'function_pointer_array' ***\n");
  OUTPUT_SOMEWHERE("Local varaiables:\n");
  dump_memory("section_function1", (unsigned char *)(&section_function1), sizeof(section_function_pointer *));
  dump_memory("section_function2", (unsigned char *)(&section_function2), sizeof(section_function_pointer *));
  dump_memory("Section contents", (unsigned char *)__start_function_pointer_array,
    (size_t) (((unsigned char *)__stop_function_pointer_array) - ((unsigned char *)__start_function_pointer_array)));
  OUTPUT_SOMEWHERE("Section contents as pointers:\n");
  for (int index = 0; &__start_function_pointer_array[index] < __stop_function_pointer_array; index++)
  {
    dump_memory("function pointer", (unsigned char *)(&__start_function_pointer_array[index]), sizeof (section_function_pointer *));
  }
  OUTPUT_SOMEWHERE("Result of calling the functions:\n");
  section_function1(NULL);
  section_function2(NULL);
  __start_function_pointer_array[0](NULL);
  __start_function_pointer_array[1](NULL);
}