title: "AVR .initN sections and GCC -flto"

---
title: "AVR .initN sections and GCC -flto"
date: 2013-02-11
---

While programming with avr-gcc I recently ran into a problem. Code placed into
the .init3 section with `__attribute__((section(".init3")))` wasn't being
included in GCC's output. The culprit ended up being GCC's -flto optimization
setting. GCC's link-time optimization (LTO) feature aggressively performs
garbage collection on unused bits of code (among other things). The AVR linker
scripts included with binutils know to always include the .initN and .finiN
sections, but by that time LTO has already discarded them. So the moral of the
story is you must add `__attribute__((used))` to your function:

```
void func(void) __attribute__((section(".init3"), naked, used));

void func(void)
{
/* code */
}
```