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Initialization/linux-initialization-6.md
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@@ -4,7 +4,7 @@ Kernel initialization. Part 6.
Architecture-specific initialization, again...
================================================================================
In the previous [part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-5.html) we saw architecture-specific (`x86_64` in our case) initialization stuff from the [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c) and finished on `x86_configure_nx` function which sets the `_PAGE_NX` flag depends on support of [NX bit](http://en.wikipedia.org/wiki/NX_bit). As I wrote before `setup_arch` function and `start_kernel` are very big, so in this and in the next part we will continue to learn about architecture-specific initialization process. The next function after `x86_configure_nx` is `parse_early_param`. This function is defined in the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c) and as you can understand from its name, this function parses kernel command line and setups different services depends on the given parameters (all kernel command line parameters you can find are in the [Documentation/kernel-parameters.txt](https://github.com/torvalds/linux/blob/master/Documentation/kernel-parameters.txt)). You may remember how we setup `earlyprintk` in the earliest [part](http://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-2.html). On the early stage we looked for kernel parameters and their value with the `cmdline_find_option` function and `__cmdline_find_option`, `__cmdline_find_option_bool` helpers from the [arch/x86/boot/cmdline.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/cmdline.c). There we're in the generic kernel part which does not depend on architecture and here we use another approach. If you are reading linux kernel source code, you already note calls like this:
In the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-5.html) we saw architecture-specific (`x86_64` in our case) initialization stuff from the [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c) and finished on `x86_configure_nx` function which sets the `_PAGE_NX` flag depends on support of [NX bit](http://en.wikipedia.org/wiki/NX_bit). As I wrote before `setup_arch` function and `start_kernel` are very big, so in this and in the next part we will continue to learn about architecture-specific initialization process. The next function after `x86_configure_nx` is `parse_early_param`. This function is defined in the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c) and as you can understand from its name, this function parses kernel command line and setups different services depends on the given parameters (all kernel command line parameters you can find are in the [Documentation/kernel-parameters.txt](https://github.com/torvalds/linux/blob/master/Documentation/kernel-parameters.txt)). You may remember how we setup `earlyprintk` in the earliest [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Booting/linux-bootstrap-2.html). On the early stage we looked for kernel parameters and their value with the `cmdline_find_option` function and `__cmdline_find_option`, `__cmdline_find_option_bool` helpers from the [arch/x86/boot/cmdline.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/cmdline.c). There we're in the generic kernel part which does not depend on architecture and here we use another approach. If you are reading linux kernel source code, you already note calls like this:
```C
early_param("gbpages", parse_direct_gbpages_on);
@@ -97,7 +97,7 @@ After this we can see call of the:
memblock_x86_reserve_range_setup_data();
```
function. This function is defined in the same [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c) source code file and remaps memory for the `setup_data` and reserved memory block for the `setup_data` (more about `setup_data` you can read in the previous [part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-5.html) and about `ioremap` and `memblock` you can read in the [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/mm/index.html)).
function. This function is defined in the same [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c) source code file and remaps memory for the `setup_data` and reserved memory block for the `setup_data` (more about `setup_data` you can read in the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-5.html) and about `ioremap` and `memblock` you can read in the [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html)).
In the next step we can see following conditional statement:
@@ -128,7 +128,7 @@ int __init acpi_mps_check(void)
}
```
It checks the built-in `MPS` or [MultiProcessor Specification](http://en.wikipedia.org/wiki/MultiProcessor_Specification) table. If `CONFIG_X86_LOCAL_APIC` is set and `CONFIG_x86_MPPAARSE` is not set, `acpi_mps_check` prints warning message if the one of the command line options: `acpi=off`, `acpi=noirq` or `pci=noacpi` passed to the kernel. If `acpi_mps_check` returns `1` it means that we disable local [APIC](http://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller) and clear `X86_FEATURE_APIC` bit in the of the current CPU with the `setup_clear_cpu_cap` macro. (more about CPU mask you can read in the [CPU masks](http://0xax.gitbooks.io/linux-insides/content/Concepts/cpumask.html)).
It checks the built-in `MPS` or [MultiProcessor Specification](http://en.wikipedia.org/wiki/MultiProcessor_Specification) table. If `CONFIG_X86_LOCAL_APIC` is set and `CONFIG_x86_MPPAARSE` is not set, `acpi_mps_check` prints warning message if the one of the command line options: `acpi=off`, `acpi=noirq` or `pci=noacpi` passed to the kernel. If `acpi_mps_check` returns `1` it means that we disable local [APIC](http://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller) and clear `X86_FEATURE_APIC` bit in the of the current CPU with the `setup_clear_cpu_cap` macro. (more about CPU mask you can read in the [CPU masks](http://xinqiu.gitbooks.io/linux-insides-cn/content/Concepts/cpumask.html)).
Early PCI dump
--------------------------------------------------------------------------------
@@ -193,7 +193,7 @@ That's all. We will not go deep in the `pci` details, but will see more details
Finish with memory parsing
--------------------------------------------------------------------------------
After the `early_dump_pci_devices`, there are a couple of function related with available memory and [e820](http://en.wikipedia.org/wiki/E820) which we collected in the [First steps in the kernel setup](http://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-2.html) part:
After the `early_dump_pci_devices`, there are a couple of function related with available memory and [e820](http://en.wikipedia.org/wiki/E820) which we collected in the [First steps in the kernel setup](http://xinqiu.gitbooks.io/linux-insides-cn/content/Booting/linux-bootstrap-2.html) part:
```C
/* update the e820_saved too */
@@ -500,7 +500,7 @@ for (; pmd < last_pmd; pmd++, vaddr += PMD_SIZE) {
}
```
After this we set the limit for the `memblock` allocation with the `memblock_set_current_limit` function (read more about `memblock` you can in the [Linux kernel memory management Part 2](https://github.com/0xAX/linux-insides/blob/master/mm/linux-mm-2.md)), it will be `ISA_END_ADDRESS` or `0x100000` and fill the `memblock` information according to `e820` with the call of the `memblock_x86_fill` function. You can see the result of this function in the kernel initialization time:
After this we set the limit for the `memblock` allocation with the `memblock_set_current_limit` function (read more about `memblock` you can in the [Linux kernel memory management Part 2](https://github.com/MintCN/linux-insides-zh/blob/master/mm/linux-mm-2.md)), it will be `ISA_END_ADDRESS` or `0x100000` and fill the `memblock` information according to `e820` with the call of the `memblock_x86_fill` function. You can see the result of this function in the kernel initialization time:
```
MEMBLOCK configuration:
@@ -536,7 +536,7 @@ Links
* [Documentation/kernel-parameters.txt](https://github.com/torvalds/linux/blob/master/Documentation/kernel-parameters.txt)
* [APIC](http://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller)
* [CPU masks](http://0xax.gitbooks.io/linux-insides/content/Concepts/cpumask.html)
* [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/mm/index.html)
* [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html)
* [PCI](http://en.wikipedia.org/wiki/Conventional_PCI)
* [e820](http://en.wikipedia.org/wiki/E820)
* [System Management BIOS](http://en.wikipedia.org/wiki/System_Management_BIOS)
@@ -546,4 +546,4 @@ Links
* [MultiProcessor Specification](http://www.intel.com/design/pentium/datashts/24201606.pdf)
* [BSS](http://en.wikipedia.org/wiki/.bss)
* [SMBIOS specification](http://www.dmtf.org/sites/default/files/standards/documents/DSP0134v2.5Final.pdf)
* [Previous part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-5.html)
* [Previous part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-5.html)