rt0.cpp

#include "rt0.h"

#include <stdint.h>
#include <string.h>

typedef void (*cxx_constructor)();

extern "C" {
void abort();
extern char _data_section_start_flash;
extern char _data_section_start_ram;
extern char _data_section_end_ram;
extern char _bss_section_start_ram;
extern char _bss_section_end_ram;
extern cxx_constructor _init_array_start;
extern cxx_constructor _init_array_end;
}

namespace Ion {
namespace Device {
namespace Init {

void configureRAM() {
  /* Copy data section to RAM
   * The data section is R/W but its initialization value matters. It's stored
   * in Flash, but linked as if it were in RAM. Now's our opportunity to copy
   * it. Note that until then the data section (e.g. global variables) contains
   * garbage values and should not be used. */
  size_t dataSectionLength =
      (&_data_section_end_ram - &_data_section_start_ram);
  memcpy(&_data_section_start_ram, &_data_section_start_flash,
         dataSectionLength);

  /* Zero-out the bss section in RAM
   * Until we do, any uninitialized global variable will be unusable. */
  size_t bssSectionLength = (&_bss_section_end_ram - &_bss_section_start_ram);
  memset(&_bss_section_start_ram, 0, bssSectionLength);

  configureGlobalVariables();
}

void configureGlobalVariables() {
  /* Call static C++ object constructors
   * The C++ compiler creates an initialization function for each static object.
   * The linker then stores the address of each of those functions consecutively
   * between _init_array_start and _init_array_end. So to initialize all C++
   * static objects we just have to iterate between theses two addresses and
   * call the pointed function. */
#define SUPPORT_CPP_GLOBAL_CONSTRUCTORS 0
#if SUPPORT_CPP_GLOBAL_CONSTRUCTORS
  for (cxx_constructor* c = &_init_array_start; c < &_init_array_end; c++) {
    (*c)();
  }
#else
  /* In practice, static initialized objects are a terrible idea. Since the init
   * order is not specified, most often than not this yields the dreaded static
   * init order fiasco. The linker asserts that the .init_array section is
   * empty. */
#endif
}

}  // namespace Init
}  // namespace Device
}  // namespace Ion