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Merge pull request #165 from NeoCui/master

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Update the linux-initialization-5.md to the latest English repo version
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Dongliang Mu
2017-10-23 09:48:35 -04:00
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Initialization/linux-initialization-5.md
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@@ -4,17 +4,17 @@ Kernel initialization. Part 5.
Continue of architecture-specific initialization
================================================================================
In the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-4.html), we stopped at the initialization of an architecture-specific stuff from the [setup_arch](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c#L856) function and now we will continue with it. As we reserved memory for the [initrd](http://en.wikipedia.org/wiki/Initrd), next step is the `olpc_ofw_detect` which detects [One Laptop Per Child support](http://wiki.laptop.org/go/OFW_FAQ). We will not consider platform related stuff in this book and will skip functions related with it. So let's go ahead. The next step is the `early_trap_init` function. This function initializes debug (`#DB` - raised when the `TF` flag of rflags is set) and `int3` (`#BP`) interrupts gate. If you don't know anything about interrupts, you can read about it in the [Early interrupt and exception handling](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-2.html). In `x86` architecture `INT`, `INTO` and `INT3` are special instructions which allow a task to explicitly call an interrupt handler. The `INT3` instruction calls the breakpoint (`#BP`) handler. You may remember, we already saw it in the [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-2.html) about interrupts: and exceptions:
In the previous [part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-4.html), we stopped at the initialization of an architecture-specific stuff from the [setup_arch](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/setup.c#L856) function and now we will continue with it. As we reserved memory for the [initrd](http://en.wikipedia.org/wiki/Initrd), next step is the `olpc_ofw_detect` which detects [One Laptop Per Child support](http://wiki.laptop.org/go/OFW_FAQ). We will not consider platform related stuff in this book and will skip functions related with it. So let's go ahead. The next step is the `early_trap_init` function. This function initializes debug (`#DB` - raised when the `TF` flag of rflags is set) and `int3` (`#BP`) interrupts gate. If you don't know anything about interrupts, you can read about it in the [Early interrupt and exception handling](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-2.html). In `x86` architecture `INT`, `INTO` and `INT3` are special instructions which allow a task to explicitly call an interrupt handler. The `INT3` instruction calls the breakpoint (`#BP`) handler. You may remember, we already saw it in the [part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-2.html) about interrupts: and exceptions:
```
----------------------------------------------------------------------------------------------
|Vector|Mnemonic|Description |Type |Error Code|Source |
|Vector|Mnemonic|Description |Type |Error Code|Source |
----------------------------------------------------------------------------------------------
|3 | #BP |Breakpoint |Trap |NO |INT 3 |
|3 | #BP |Breakpoint |Trap |NO |INT 3 |
----------------------------------------------------------------------------------------------
```
Debug interrupt `#DB` is the primary method of invoking debuggers. `early_trap_init` defined in the [arch/x86/kernel/traps.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/traps.c). This functions sets `#DB` and `#BP` handlers and reloads [IDT](http://en.wikipedia.org/wiki/Interrupt_descriptor_table):
Debug interrupt `#DB` is the primary method of invoking debuggers. `early_trap_init` defined in the [arch/x86/kernel/traps.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/traps.c). This functions sets `#DB` and `#BP` handlers and reloads [IDT](http://en.wikipedia.org/wiki/Interrupt_descriptor_table):
```C
void __init early_trap_init(void)
@@ -29,7 +29,9 @@ We already saw implementation of the `set_intr_gate` in the previous part about
* number of the interrupt;
* base address of the interrupt/exception handler;
* third parameter is - `Interrupt Stack Table`. `IST` is a new mechanism in the `x86_64` and part of the [TSS](http://en.wikipedia.org/wiki/Task_state_segment). Every active thread in kernel mode has own kernel stack which is 16 kilobytes. While a thread in user space, kernel stack is empty except `thread_info` (read about it previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-4.html)) at the bottom. In addition to per-thread stacks, there are a couple of specialized stacks associated with each CPU. All about these stack you can read in the linux kernel documentation - [Kernel stacks](https://www.kernel.org/doc/Documentation/x86/x86_64/kernel-stacks). `x86_64` provides feature which allows to switch to a new `special` stack for during any events as non-maskable interrupt and etc... And the name of this feature is - `Interrupt Stack Table`. There can be up to 7 `IST` entries per CPU and every entry points to the dedicated stack. In our case this is `DEBUG_STACK`.
* third parameter is - `Interrupt Stack Table`. `IST` is a new mechanism in the `x86_64` and part of the [TSS](http://en.wikipedia.org/wiki/Task_state_segment). Every active thread in kernel mode has own kernel stack which is `16` kilobytes. While a thread in user space, this kernel stack is empty.
In addition to per-thread stacks, there are a couple of specialized stacks associated with each CPU. All about these stack you can read in the linux kernel documentation - [Kernel stacks](https://www.kernel.org/doc/Documentation/x86/x86_64/kernel-stacks). `x86_64` provides feature which allows to switch to a new `special` stack for during any events as non-maskable interrupt and etc... And the name of this feature is - `Interrupt Stack Table`. There can be up to 7 `IST` entries per CPU and every entry points to the dedicated stack. In our case this is `DEBUG_STACK`.
`set_intr_gate_ist` and `set_system_intr_gate_ist` work by the same principle as `set_intr_gate` with only one difference. Both of these functions checks
interrupt number and call `_set_gate` inside:
@@ -39,20 +41,20 @@ BUG_ON((unsigned)n > 0xFF);
_set_gate(n, GATE_INTERRUPT, addr, 0, ist, __KERNEL_CS);
```
as `set_intr_gate` does this. But `set_intr_gate` calls `_set_gate` with [dpl](http://en.wikipedia.org/wiki/Privilege_level) - 0, and ist - 0, but `set_intr_gate_ist` and `set_system_intr_gate_ist` sets `ist` as `DEBUG_STACK` and `set_system_intr_gate_ist` sets `dpl` as `0x3` which is the lowest privilege. When an interrupt occurs and the hardware loads such a descriptor, then hardware automatically sets the new stack pointer based on the IST value, then invokes the interrupt handler. All of the special kernel stacks will be setted in the `cpu_init` function (we will see it later).
as `set_intr_gate` does this. But `set_intr_gate` calls `_set_gate` with [dpl](http://en.wikipedia.org/wiki/Privilege_level) - 0, and ist - 0, but `set_intr_gate_ist` and `set_system_intr_gate_ist` sets `ist` as `DEBUG_STACK` and `set_system_intr_gate_ist` sets `dpl` as `0x3` which is the lowest privilege. When an interrupt occurs and the hardware loads such a descriptor, then hardware automatically sets the new stack pointer based on the IST value, then invokes the interrupt handler. All of the special kernel stacks will be set in the `cpu_init` function (we will see it later).
As `#DB` and `#BP` gates written to the `idt_descr`, we reload `IDT` table with `load_idt` which just cals `ldtr` instruction. Now let's look on interrupt handlers and will try to understand how they works. Of course, I can't cover all interrupt handlers in this book and I do not see the point in this. It is very interesting to delve in the linux kernel source code, so we will see how `debug` handler implemented in this part, and understand how other interrupt handlers are implemented will be your task.
As `#DB` and `#BP` gates written to the `idt_descr`, we reload `IDT` table with `load_idt` which just calss `ldtr` instruction. Now let's look on interrupt handlers and will try to understand how they works. Of course, I can't cover all interrupt handlers in this book and I do not see the point in this. It is very interesting to delve in the linux kernel source code, so we will see how `debug` handler implemented in this part, and understand how other interrupt handlers are implemented will be your task.
#DB handler
--------------------------------------------------------------------------------
As you can read above, we passed address of the `#DB` handler as `&debug` in the `set_intr_gate_ist`. [lxr.free-electorns.com](http://lxr.free-electrons.com/ident) is a great resource for searching identifiers in the linux kernel source code, but unfortunately you will not find `debug` handler with it. All of you can find, it is `debug` definition in the [arch/x86/include/asm/traps.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/traps.h):
As you can read above, we passed address of the `#DB` handler as `&debug` in the `set_intr_gate_ist`. [lxr.free-electrons.com](http://lxr.free-electrons.com/ident) is a great resource for searching identifiers in the linux kernel source code, but unfortunately you will not find `debug` handler with it. All of you can find, it is `debug` definition in the [arch/x86/include/asm/traps.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/include/asm/traps.h):
```C
asmlinkage void debug(void);
```
We can see `asmlinkage` attribute which tells to us that `debug` is function written with [assembly](http://en.wikipedia.org/wiki/Assembly_language). Yeah, again and again assembly :). Implementation of the `#DB` handler as other handlers is in this [arch/x86/kernel/entry_64.S](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/entry_64.S) and defined with the `idtentry` assembly macro:
We can see `asmlinkage` attribute which tells to us that `debug` is function written with [assembly](http://en.wikipedia.org/wiki/Assembly_language). Yeah, again and again assembly :). Implementation of the `#DB` handler as other handlers is in this [arch/x86/kernel/entry_64.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/entry_64.S) and defined with the `idtentry` assembly macro:
```assembly
idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
@@ -66,7 +68,7 @@ idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
* paranoid - if this parameter = 1, switch to special stack (read above);
* shift_ist - stack to switch during interrupt.
Now let's look on `idtentry` macro implementation. This macro defined in the same assembly file and defines `debug` function with the `ENTRY` macro. For the start `idtentry` macro checks that given parameters are correct in case if need to switch to the special stack. In the next step it checks that give interrupt returns error code. If interrupt does not return error code (in our case `#DB` does not return error code), it calls `INTR_FRAME` or `XCPT_FRAME` if interrupt has error code. Both of these macros `XCPT_FRAME` and `INTR_FRAME` do nothing and need only for the building initial frame state for interrupts. They uses `CFI` directives and used for debugging. More info you can find in the [CFI directives](https://sourceware.org/binutils/docs/as/CFI-directives.html). As comment from the [arch/x86/kernel/entry_64.S](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/entry_64.S) says: `CFI macros are used to generate dwarf2 unwind information for better backtraces. They don't change any code.` so we will ignore them.
Now let's look on `idtentry` macro implementation. This macro defined in the same assembly file and defines `debug` function with the `ENTRY` macro. For the start `idtentry` macro checks that given parameters are correct in case if need to switch to the special stack. In the next step it checks that give interrupt returns error code. If interrupt does not return error code (in our case `#DB` does not return error code), it calls `INTR_FRAME` or `XCPT_FRAME` if interrupt has error code. Both of these macros `XCPT_FRAME` and `INTR_FRAME` do nothing and need only for the building initial frame state for interrupts. They uses `CFI` directives and used for debugging. More info you can find in the [CFI directives](https://sourceware.org/binutils/docs/as/CFI-directives.html). As comment from the [arch/x86/kernel/entry_64.S](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/entry_64.S) says: `CFI macros are used to generate dwarf2 unwind information for better backtraces. They don't change any code.` so we will ignore them.
```assembly
.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
@@ -124,7 +126,7 @@ We need to do it as `dummy` error code for stack consistency for all interrupts.
subq $ORIG_RAX-R15, %rsp
```
where `ORIRG_RAX`, `R15` and other macros defined in the [arch/x86/include/asm/calling.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/calling.h) and `ORIG_RAX-R15` is 120 bytes. General purpose registers will occupy these 120 bytes because we need to store all registers on the stack during interrupt handling. After we set stack for general purpose registers, the next step is checking that interrupt came from userspace with:
where `ORIRG_RAX`, `R15` and other macros defined in the [arch/x86/include/asm/calling.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/include/asm/calling.h) and `ORIG_RAX-R15` is 120 bytes. General purpose registers will occupy these 120 bytes because we need to store all registers on the stack during interrupt handling. After we set stack for general purpose registers, the next step is checking that interrupt came from userspace with:
```assembly
testl $3, CS(%rsp)
@@ -144,14 +146,14 @@ Here we checks first and second bits in the `CS`. You can remember that `CS` reg
1: ret
```
In the next steps we put `pt_regs` pointer to the `rdi`, save error code in the `rsi` if it has and call interrupt handler which is - `do_debug` in our case from the [arch/x86/kernel/traps.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/traps.c). `do_debug` like other handlers takes two parameters:
In the next steps we put `pt_regs` pointer to the `rdi`, save error code in the `rsi` if it has and call interrupt handler which is - `do_debug` in our case from the [arch/x86/kernel/traps.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/traps.c). `do_debug` like other handlers takes two parameters:
* pt_regs - is a structure which presents set of CPU registers which are saved in the process' memory region;
* error code - error code of interrupt.
After interrupt handler finished its work, calls `paranoid_exit` which restores stack, switch on userspace if interrupt came from there and calls `iret`. That's all. Of course it is not all :), but we will see more deeply in the separate chapter about interrupts.
This is general view of the `idtentry` macro for `#DB` interrupt. All interrupts are similar to this implementation and defined with idtentry too. After `early_trap_init` finished its work, the next function is `early_cpu_init`. This function defined in the [arch/x86/kernel/cpu/common.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/cpu/common.c) and collects information about CPU and its vendor.
This is general view of the `idtentry` macro for `#DB` interrupt. All interrupts are similar to this implementation and defined with idtentry too. After `early_trap_init` finished its work, the next function is `early_cpu_init`. This function defined in the [arch/x86/kernel/cpu/common.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/cpu/common.c) and collects information about CPU and its vendor.
Early ioremap initialization
--------------------------------------------------------------------------------
@@ -161,16 +163,16 @@ The next step is initialization of early `ioremap`. In general there are two way
* I/O Ports;
* Device memory.
We already saw first method (`outb/inb` instructions) in the part about linux kernel booting [process](http://xinqiu.gitbooks.io/linux-insides-cn/content/Booting/linux-bootstrap-3.html). The second method is to map I/O physical addresses to virtual addresses. When a physical address is accessed by the CPU, it may refer to a portion of physical RAM which can be mapped on memory of the I/O device. So `ioremap` used to map device memory into kernel address space.
We already saw first method (`outb/inb` instructions) in the part about linux kernel booting [process](http://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-3.html). The second method is to map I/O physical addresses to virtual addresses. When a physical address is accessed by the CPU, it may refer to a portion of physical RAM which can be mapped on memory of the I/O device. So `ioremap` used to map device memory into kernel address space.
As i wrote above next function is the `early_ioremap_init` which re-maps I/O memory to kernel address space so it can access it. We need to initialize early ioremap for early initialization code which needs to temporarily map I/O or memory regions before the normal mapping functions like `ioremap` are available. Implementation of this function is in the [arch/x86/mm/ioremap.c](https://github.com/torvalds/linux/blob/master/arch/x86/mm/ioremap.c). At the start of the `early_ioremap_init` we can see definition of the `pmd` point with `pmd_t` type (which presents page middle directory entry `typedef struct { pmdval_t pmd; } pmd_t;` where `pmdval_t` is `unsigned long`) and make a check that `fixmap` aligned in a correct way:
As i wrote above next function is the `early_ioremap_init` which re-maps I/O memory to kernel address space so it can access it. We need to initialize early ioremap for early initialization code which needs to temporarily map I/O or memory regions before the normal mapping functions like `ioremap` are available. Implementation of this function is in the [arch/x86/mm/ioremap.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/mm/ioremap.c). At the start of the `early_ioremap_init` we can see definition of the `pmd` point with `pmd_t` type (which presents page middle directory entry `typedef struct { pmdval_t pmd; } pmd_t;` where `pmdval_t` is `unsigned long`) and make a check that `fixmap` aligned in a correct way:
```C
pmd_t *pmd;
BUILD_BUG_ON((fix_to_virt(0) + PAGE_SIZE) & ((1 << PMD_SHIFT) - 1));
```
`fixmap` - is fixed virtual address mappings which extends from `FIXADDR_START` to `FIXADDR_TOP`. Fixed virtual addresses are needed for subsystems that need to know the virtual address at compile time. After the check `early_ioremap_init` makes a call of the `early_ioremap_setup` function from the [mm/early_ioremap.c](https://github.com/torvalds/linux/blob/master/mm/early_ioremap.c). `early_ioremap_setup` fills `slot_virt` array of the `unsigned long` with virtual addresses with 512 temporary boot-time fix-mappings:
`fixmap` - is fixed virtual address mappings which extends from `FIXADDR_START` to `FIXADDR_TOP`. Fixed virtual addresses are needed for subsystems that need to know the virtual address at compile time. After the check `early_ioremap_init` makes a call of the `early_ioremap_setup` function from the [mm/early_ioremap.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/mm/early_ioremap.c). `early_ioremap_setup` fills `slot_virt` array of the `unsigned long` with virtual addresses with 512 temporary boot-time fix-mappings:
```C
for (i = 0; i < FIX_BTMAPS_SLOTS; i++)
@@ -185,7 +187,7 @@ memset(bm_pte, 0, sizeof(bm_pte));
pmd_populate_kernel(&init_mm, pmd, bm_pte);
```
That's all for this. If you feeling puzzled, don't worry. There is special part about `ioremap` and `fixmaps` in the [Linux Kernel Memory Management. Part 2](https://github.com/MintCN/linux-insides-zh/blob/master/mm/linux-mm-2.md) chapter.
That's all for this. If you feeling puzzled, don't worry. There is special part about `ioremap` and `fixmaps` in the [Linux Kernel Memory Management. Part 2](https://github.com/0xAX/linux-insides/blob/master/mm/linux-mm-2.md) chapter.
Obtaining major and minor numbers for the root device
--------------------------------------------------------------------------------
@@ -233,7 +235,7 @@ After calculation we will get `0xfff` or 12 bits for `major` if it is `0xfffffff
Memory map setup
--------------------------------------------------------------------------------
The next point is the setup of the memory map with the call of the `setup_memory_map` function. But before this we setup different parameters as information about a screen (current row and column, video page and etc... (you can read about it in the [Video mode initialization and transition to protected mode](http://xinqiu.gitbooks.io/linux-insides-cn/content/Booting/linux-bootstrap-3.html))), Extended display identification data, video mode, bootloader_type and etc...:
The next point is the setup of the memory map with the call of the `setup_memory_map` function. But before this we setup different parameters as information about a screen (current row and column, video page and etc... (you can read about it in the [Video mode initialization and transition to protected mode](http://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-3.html))), Extended display identification data, video mode, bootloader_type and etc...:
```C
screen_info = boot_params.screen_info;
@@ -284,7 +286,7 @@ struct resource {
};
```
presents abstraction for a tree-like subset of system resources. This structure provides range of addresses from `start` to `end` (`resource_size_t` is `phys_addr_t` or `u64` for `x86_64`) which a resource covers, `name` of a resource (you see these names in the `/proc/iomem` output) and `flags` of a resource (All resources flags defined in the [include/linux/ioport.h](https://github.com/torvalds/linux/blob/master/include/linux/ioport.h)). The last are three pointers to the `resource` structure. These pointers enable a tree-like structure:
presents abstraction for a tree-like subset of system resources. This structure provides range of addresses from `start` to `end` (`resource_size_t` is `phys_addr_t` or `u64` for `x86_64`) which a resource covers, `name` of a resource (you see these names in the `/proc/iomem` output) and `flags` of a resource (All resources flags defined in the [include/linux/ioport.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/include/linux/ioport.h)). The last are three pointers to the `resource` structure. These pointers enable a tree-like structure:
```
+-------------+ +-------------+
@@ -337,7 +339,7 @@ void __init setup_memory_map(void)
}
```
First of all we call look here the call of the `x86_init.resources.memory_setup`. `x86_init` is a `x86_init_ops` structure which presents platform specific setup functions as resources initialization, pci initialization and etc... initialization of the `x86_init` is in the [arch/x86/kernel/x86_init.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/x86_init.c). I will not give here the full description because it is very long, but only one part which interests us for now:
First of all we call look here the call of the `x86_init.resources.memory_setup`. `x86_init` is a `x86_init_ops` structure which presents platform specific setup functions as resources initialization, pci initialization and etc... initialization of the `x86_init` is in the [arch/x86/kernel/x86_init.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/x86_init.c). I will not give here the full description because it is very long, but only one part which interests us for now:
```C
struct x86_init_ops x86_init __initdata = {
@@ -352,7 +354,7 @@ struct x86_init_ops x86_init __initdata = {
}
```
As we can see here `memry_setup` field is `default_machine_specific_memory_setup` where we get the number of the [e820](http://en.wikipedia.org/wiki/E820) entries which we collected in the [boot time](http://xinqiu.gitbooks.io/linux-insides-cn/content/Booting/linux-bootstrap-2.html), sanitize the BIOS e820 map and fill `e820map` structure with the memory regions. As all regions are collected, print of all regions with printk. You can find this print if you execute `dmesg` command and you can see something like this:
As we can see here `memry_setup` field is `default_machine_specific_memory_setup` where we get the number of the [e820](http://en.wikipedia.org/wiki/E820) entries which we collected in the [boot time](http://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-2.html), sanitize the BIOS e820 map and fill `e820map` structure with the memory regions. As all regions are collected, print of all regions with printk. You can find this print if you execute `dmesg` command and you can see something like this:
```
[ 0.000000] e820: BIOS-provided physical RAM map:
@@ -390,7 +392,7 @@ Protocol: 2.09+
parameters passing mechanism.
```
It used for storing setup information for different types as device tree blob, EFI setup data and etc... In the second step we copy BIOS EDD information from the `boot_params` structure that we collected in the [arch/x86/boot/edd.c](https://github.com/torvalds/linux/blob/master/arch/x86/boot/edd.c) to the `edd` structure:
It used for storing setup information for different types as device tree blob, EFI setup data and etc... In the second step we copy BIOS EDD information from the `boot_params` structure that we collected in the [arch/x86/boot/edd.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/edd.c) to the `edd` structure:
```C
static inline void __init copy_edd(void)
@@ -406,7 +408,7 @@ static inline void __init copy_edd(void)
Memory descriptor initialization
--------------------------------------------------------------------------------
The next step is initialization of the memory descriptor of the init process. As you already can know every process has its own address space. This address space presented with special data structure which called `memory descriptor`. Directly in the linux kernel source code memory descriptor presented with `mm_struct` structure. `mm_struct` contains many different fields related with the process address space as start/end address of the kernel code/data, start/end of the brk, number of memory areas, list of memory areas and etc... This structure defined in the [include/linux/mm_types.h](https://github.com/torvalds/linux/blob/master/include/linux/mm_types.h). As every process has its own memory descriptor, `task_struct` structure contains it in the `mm` and `active_mm` field. And our first `init` process has it too. You can remember that we saw the part of initialization of the init `task_struct` with `INIT_TASK` macro in the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-4.html):
The next step is initialization of the memory descriptor of the init process. As you already can know every process has its own address space. This address space presented with special data structure which called `memory descriptor`. Directly in the linux kernel source code memory descriptor presented with `mm_struct` structure. `mm_struct` contains many different fields related with the process address space as start/end address of the kernel code/data, start/end of the brk, number of memory areas, list of memory areas and etc... This structure defined in the [include/linux/mm_types.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/include/linux/mm_types.h). As every process has its own memory descriptor, `task_struct` structure contains it in the `mm` and `active_mm` field. And our first `init` process has it too. You can remember that we saw the part of initialization of the init `task_struct` with `INIT_TASK` macro in the previous [part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-4.html):
```C
#define INIT_TASK(tsk) \
@@ -464,7 +466,7 @@ We already know a little about `resource` structure (read above). Here we fills
01a11000-01ac3fff : Kernel bss
```
All of these structures are defined in the [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c) and look like typical resource initialization:
All of these structures are defined in the [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/setup.c) and look like typical resource initialization:
```C
static struct resource code_resource = {
@@ -490,11 +492,11 @@ void x86_configure_nx(void)
Conclusion
--------------------------------------------------------------------------------
It is the end of the fifth part about linux kernel initialization process. In this part we continued to dive in the `setup_arch` function which makes initialization of architecture-specific stuff. It was long part, but we have not finished with it. As i already wrote, the `setup_arch` is big function, and I am really not sure that we will cover all of it even in the next part. There were some new interesting concepts in this part like `Fix-mapped` addresses, ioremap and etc... Don't worry if they are unclear for you. There is a special part about these concepts - [Linux kernel memory management Part 2.](https://github.com/MintCN/linux-insides-zh/blob/master/mm/linux-mm-2.md). In the next part we will continue with the initialization of the architecture-specific stuff and will see parsing of the early kernel parameters, early dump of the pci devices, direct Media Interface scanning and many many more.
It is the end of the fifth part about linux kernel initialization process. In this part we continued to dive in the `setup_arch` function which makes initialization of architecture-specific stuff. It was long part, but we have not finished with it. As i already wrote, the `setup_arch` is big function, and I am really not sure that we will cover all of it even in the next part. There were some new interesting concepts in this part like `Fix-mapped` addresses, ioremap and etc... Don't worry if they are unclear for you. There is a special part about these concepts - [Linux kernel memory management Part 2.](https://github.com/0xAX/linux-insides/blob/master/mm/linux-mm-2.md). In the next part we will continue with the initialization of the architecture-specific stuff and will see parsing of the early kernel parameters, early dump of the pci devices, direct Media Interface scanning and many many more.
If you have any questions or suggestions write me a comment or ping me at [twitter](https://twitter.com/0xAX).
**Please note that English is not my first language, And I am really sorry for any inconvenience. If you find any mistakes please send me PR to [linux-insides](https://github.com/MintCN/linux-insides-zh).**
**Please note that English is not my first language, And I am really sorry for any inconvenience. If you find any mistakes please send me PR to [linux-insides](https://github.com/0xAX/linux-insides).**
Links
--------------------------------------------------------------------------------
@@ -509,4 +511,4 @@ Links
* [CFI directives](https://sourceware.org/binutils/docs/as/CFI-directives.html)
* [PDF. dwarf4 specification](http://dwarfstd.org/doc/DWARF4.pdf)
* [Call stack](http://en.wikipedia.org/wiki/Call_stack)
* [Previous part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-4.html)
* [Previous part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-4.html)

2
README.md
View File

@@ -34,7 +34,7 @@
|├ [2.2](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-2.md)|[@dontpanic92](https://github.com/dontpanic92)|更新至[44017507](https://github.com/0xAX/linux-insides/commit/4401750766f7150dcd16f579026f5554541a6ab9)|
|├ [2.3](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-3.md)|[@dontpanic92](https://github.com/dontpanic92)|更新至[44017507](https://github.com/0xAX/linux-insides/commit/4401750766f7150dcd16f579026f5554541a6ab9)|
|├ [2.4](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-4.md)||已完成|
|├ [2.5](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-5.md)||未开始|
|├ [2.5](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-5.md)||正在进行|
|├ [2.6](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-6.md)||未开始|
|├ [2.7](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-7.md)||未开始|
|├ [2.8](https://github.com/MintCN/linux-insides-zh/blob/master/Initialization/linux-initialization-8.md)||未开始|