C++ in ARM MCU: Need help to set up a simple timer - c++

Question

I'm programming an ATSAME70 and I'm trying to program a simple timer using the SysTick interrupt available in Cortex M MCUs, but I don't know what is going wrong.
If write this code in a simple main.cpp file:
// main.cpp
#include <cstdint>
#include "init.h"
#include "led.hpp"
volatile uint32_t g_ticks = 0;
extern "C" {
void SysTick_Handler(void)
{
g_ticks++;
}
}
class Timer
{
private:
uint32_t start;
public:
Timer() : start(g_ticks) {}
float elapsed() const { return (g_ticks - start) / 1000.0f; }
};
int main()
{
init();
SysTick_Config(300000000 / 1000); /* Clock is running at 300 MHz */
Timer t;
while (t.elapsed() < 1.0f);
Led::on();
while (true);
}
It works, the led lights up properly after 1 second.
But if I try to keep it clean and separate the program in the following files:
// timer.hpp
#include <cstdint>
class Timer
{
private:
uint32_t start;
public:
Timer();
float elapsed() const;
};
// timer.cpp
#include "timer.hpp"
volatile uint32_t g_ticks = 0;
extern "C" {
void SysTick_Handler(void)
{
g_ticks++;
}
}
Timer::Timer() : start(g_ticks) {}
float Timer::elapsed() const
{
return (g_ticks - start) / 1000.0f;
}
// main.cpp
#include <cstdint>
#include "init.h"
#include "led.hpp"
#include "timer.hpp"
int main()
{
init();
SysTick_Config(300000000 / 1000); /* Clock is running at 300 MHz */
Timer t;
while (t.elapsed() < 1.0f);
Led::on();
while (true);
}
It doesn't work anymore, the program reaches the first while loop and then it gets stuck there, I think g_ticks is being corrupted when I try to read it in t.elapsed() but I don't know what is happening. Does anybody know where I'm wrong?
init() is just a function in which I initialize all needed registers.
EDIT: here are the command lines used to generate the code:
$toolchain_path = "C:\Program Files (x86)\GNU Tools ARM Embedded\8 2018-q4-major\bin";
$link_file = "source\device\same70_flash.ld"
$c_files = "include\sensors\bmi088\bmi088.c " +
...
"source\utils\syscalls.c";
$cpp_files = "source\device\init.cpp " +
...
"source\main.cpp";
Invoke-Expression "& '$toolchain_path\arm-none-eabi-gcc.exe' -c -s -O3 -fdata-sections -ffunction-sections '-Wl,--gc-sections' '-Wl,--entry=Reset_Handler' -mthumb -mcpu=cortex-m7 -mfloat-abi=hard -mfpu=fpv5-d16 -Isource -Iinclude\CMSIS -D__SAME70N21__ $c_files --specs=nosys.specs"
foreach ($c_file in $c_files.split(" "))
{
if ($objects) { $objects += " "; }
$objects += ($c_file.split("\")[-1]).split(".")[0] + ".o";
}
Invoke-Expression "& '$toolchain_path\arm-none-eabi-ld.exe' -s --entry=Reset_Handler -r $objects -o drivers.o"
foreach ($object in $objects.split(" ")) { Remove-Item $object; }
Move-Item drivers.o bin\drivers.o -force
Invoke-Expression "& '$toolchain_path\arm-none-eabi-g++.exe' -s -O3 -fdata-sections -ffunction-sections '-Wl,--gc-sections' -mthumb -mcpu=cortex-m7 -mfloat-abi=hard -mfpu=fpv5-d16 '-Wl,--entry=Reset_Handler' -std=c++17 -Isource -Iinclude -Iinclude\CMSIS -D__SAME70N21__ bin/drivers.o $cpp_files --specs=nosys.specs -T $link_file -o bin\code.elf"
Invoke-Expression "& '$toolchain_path\arm-none-eabi-objcopy.exe' -O binary bin\code.elf bin\code.bin"
The script is written in powershell and I'll explain it a little bit. $c_files is just a string with every c file to be compiled separated by an space. $objects is an array of strings containing every file listed in $c_files but with the ".c" extension replaced by ".o". I've done this to link every c compiled file into "drivers.o". Finally, c++ code is compiled using this drivers.o as argument and then I generate the .bin file to upload it to the MCU.
The code is compiled using the latest GNU Arm Embedded toolchain. I must have made a mistake somewhere but I don't know where and I don't have a debugger to debug the code at runtime.
EDIT 2: Both variants work properly without optimizations. If I pass -O1 or higher as argument to the compiler the second variant stops working and I don't understand why.