We started to dive into linux kernel internals in the previous [part](https://github.com/0xAX/linux-insides/blob/master/boot/linux-bootstrap-1.md) and saw the initial part of the kernel setup code. We stopped at the first call of the `main` function (which is the first function written in C) from [arch/x86/boot/main.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c). Here we will continue to research of the kernel setup code and see what is `protected mode`, some preparation for transition to it, the heap and console initialization, memory detection and many many more. So... Let's go ahead.
We started to dive into linux kernel internals in the previous [part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-1.md) and saw the initial part of the kernel setup code. We stopped at the first call of the `main` function (which is the first function written in C) from [arch/x86/boot/main.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c). Here we will continue to research of the kernel setup code and see what is `protected mode`, some preparation for transition to it, the heap and console initialization, memory detection and many many more. So... Let's go ahead.
After the stack and bss section were prepared in the [header.S](https://github.com/torvalds/linux/blob/master/arch/x86/boot/header.S) (see previous [part](https://github.com/0xAX/linux-insides/blob/master/boot/linux-bootstrap-1.md)), need to initialize the [heap](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c#L116) with the [init_heap](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c#L116) function.
After the stack and bss section were prepared in the [header.S](https://github.com/torvalds/linux/blob/master/arch/x86/boot/header.S) (see previous [part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-1.md)), need to initialize the [heap](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c#L116) with the [init_heap](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c#L116) function.
First of all `init_heap` checks `CAN_USE_HEAP` flag from the `loadflags` kernel setup header and calculates end of the stack if this flag was set:
0xAX
9 years ago