What is -ffreestanding option in gcc?

c gcc compilation freestanding
saplingPro picture saplingPro · Jul 17, 2013 · Viewed 30.4k times · Source

What is ffreestanding in gcc ? What is it used for ? I came across the following :

gcc -ffreestanding -m32 -c kernel.c -o kernel.o

and do not understand, what does it mean exactly.

Answer

Dayal rai picture Dayal rai · Jul 17, 2013

A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at "main". The option -ffreestanding directs the compiler to not assume that standard functions have their usual definition.

By default, GCC will act as the compiler for a hosted implementation, defining __STDC_HOSTED__ as 1 and presuming that when the names of ISO C functions are used, they have the semantics defined in the standard. To make it act as a conforming freestanding implementation for a freestanding environment, use the option -ffreestanding. It will then define __STDC_HOSTED__ to 0, and not make assumptions about the meanings of function names from the standard library.

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