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Make links to other parts relative
Links to other parts had absolute URLs, so they were pointing to the same page, regardless of where they were located. E.g. pages on gitbooks links to github. Make them relative, so they are pointing to the host on which the are located.
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Hudd
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@ -4,7 +4,7 @@ Kernel booting process. Part 2.
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First steps in the kernel setup
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--------------------------------------------------------------------------------
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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.
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We started to dive into linux kernel internals in the previous [part](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.
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Protected mode
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@ -266,7 +266,7 @@ After that `biosregs` structure filled with `memset`, `bios_putchar` calls [0x10
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Heap initialization
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--------------------------------------------------------------------------------
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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.
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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](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.
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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:
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@ -464,4 +464,4 @@ Links
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* [Intel SpeedStep](http://en.wikipedia.org/wiki/SpeedStep)
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* [APM](https://en.wikipedia.org/wiki/Advanced_Power_Management)
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* [EDD specification](http://www.t13.org/documents/UploadedDocuments/docs2004/d1572r3-EDD3.pdf)
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* [Previous part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-1.md)
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* [Previous part](linux-bootstrap-1.md)
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@ -4,9 +4,9 @@ Kernel booting process. Part 3.
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Video mode initialization and transition to protected mode
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--------------------------------------------------------------------------------
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This is the third part of the `Kernel booting process` series. In the previous [part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-2.md#kernel-booting-process-part-2), we stopped right before the call of the `set_video` routine from the [main.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c#L181). We will see video mode initialization in the kernel setup code, preparation before switching into the protected mode and transition into it in this part.
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This is the third part of the `Kernel booting process` series. In the previous [part](linux-bootstrap-2.md#kernel-booting-process-part-2), we stopped right before the call of the `set_video` routine from the [main.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/main.c#L181). We will see video mode initialization in the kernel setup code, preparation before switching into the protected mode and transition into it in this part.
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**NOTE** If you don't know anything about protected mode, you can find some information about it in the previous [part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-2.md#protected-mode). Also there are a couple of [links](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-2.md#links) which can help you.
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**NOTE** If you don't know anything about protected mode, you can find some information about it in the previous [part](linux-bootstrap-2.md#protected-mode). Also there are a couple of [links](linux-bootstrap-2.md#links) which can help you.
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As i wrote above, we will start from the `set_video` function which defined in the [arch/x86/boot/video.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/video.c#L315) source code file. We can see that it starts with getting of video mode from the `boot_params.hdr` structure:
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@ -118,7 +118,7 @@ static inline bool heap_free(size_t n)
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}
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```
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which subtracts value of the `HEAP` from the `heap_end` (we calculated it in the previous [part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-2.md)) and returns 1 if there is enough memory for `n`.
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which subtracts value of the `HEAP` from the `heap_end` (we calculated it in the previous [part](linux-bootstrap-2.md)) and returns 1 if there is enough memory for `n`.
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That's all. Now we have simple API for heap and can setup video mode.
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@ -351,7 +351,7 @@ where we can see - 16-bit length of IDT and 32-bit pointer to it (More details a
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Setup Global Descriptor Table
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--------------------------------------------------------------------------------
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The next point is setup of the Global Descriptor Table (GDT). We can see `setup_gdt` function which setups GDT (you can read about it in the [Kernel booting process. Part 2.](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-2.md#protected-mode)). There is definition of the `boot_gdt` array in this function, which contains definition of the three segments:
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The next point is setup of the Global Descriptor Table (GDT). We can see `setup_gdt` function which setups GDT (you can read about it in the [Kernel booting process. Part 2.](linux-bootstrap-2.md#protected-mode)). There is definition of the `boot_gdt` array in this function, which contains definition of the three segments:
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```C
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static const u64 boot_gdt[] __attribute__((aligned(16))) = {
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@ -389,7 +389,7 @@ int main(void)
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Technically structure which contains one `int` field, must be 4 bytes, but here `aligned` structure will be 16 bytes:
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```
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$ gcc test.c -o test && ./test
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$ gcc test.c -o test && test
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Not aligned - 4
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Aligned - 16
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```
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@ -421,7 +421,7 @@ in binary. Let's try to understand what every bit means. We will go through all
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* 101 - segment type execute/read/
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* 1 - accessed bit
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You can know more about every bit in the previous [post](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-2.md) or in the [Intel® 64 and IA-32 Architectures Software Developer’s Manuals 3A](http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html).
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You can know more about every bit in the previous [post](linux-bootstrap-2.md) or in the [Intel® 64 and IA-32 Architectures Software Developer’s Manuals 3A](http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html).
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After this we get length of GDT with:
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@ -538,4 +538,4 @@ Links
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* [A20](http://en.wikipedia.org/wiki/A20_line)
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* [GCC designated inits](https://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Designated-Inits.html)
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* [GCC type attributes](https://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html)
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* [Previous part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-2.md)
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* [Previous part](linux-bootstrap-2.md)
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