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Fix a few minor typos

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Jeremy Cline 2016-06-04 11:14:24 -04:00
parent 6c34660782
commit 4aa8cbcc60
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2 changed files with 4 additions and 3 deletions
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6
Booting/linux-bootstrap-4.md
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@ -311,7 +311,7 @@ In simple terms this means that the Linux kernel with the same configuration can
KBUILD_CFLAGS += -fno-strict-aliasing -fPIC KBUILD_CFLAGS += -fno-strict-aliasing -fPIC
``` ```
When we are using position-independent code an address obtained by adding the address field of the command and the value of the program counter. We can load a code which is uses such addressing from any address. That's why we had to get the real physical address of `startup_32`. Now let's get back to the Linux kernel code. Our current goal is to calculate an address where we can relocate the kernel for decompression. Calculation of this address depends on `CONFIG_RELOCATABLE` kernel configuration option. Let's look at the code: When we are using position-independent code an address is obtained by adding the address field of the command and the value of the program counter. We can load code which uses such addressing from any address. That's why we had to get the real physical address of `startup_32`. Now let's get back to the Linux kernel code. Our current goal is to calculate an address where we can relocate the kernel for decompression. Calculation of this address depends on `CONFIG_RELOCATABLE` kernel configuration option. Let's look at the code:
```assembly ```assembly
#ifdef CONFIG_RELOCATABLE #ifdef CONFIG_RELOCATABLE
@ -329,7 +329,7 @@ When we are using position-independent code an address obtained by adding the ad
addl $z_extract_offset, %ebx addl $z_extract_offset, %ebx
``` ```
Remember that value of the `ebp` register is the physical address of the `startup_32` label. If the `CONFIG_RELOCATABLE` kernel configuration option is enabled during kernel configuration, we put this address in the `ebx` register, align it to a multiple of `2MB` and compare it with the `LOAD_PHYSICAL_ADDR` value. The `LOAD_PHYSICAL_ADDR` macro is defined in the [arch/x86/include/asm/boot.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/boot.h) header file and it looks like this: Remember that the value of the `ebp` register is the physical address of the `startup_32` label. If the `CONFIG_RELOCATABLE` kernel configuration option is enabled during kernel configuration, we put this address in the `ebx` register, align it to a multiple of `2MB` and compare it with the `LOAD_PHYSICAL_ADDR` value. The `LOAD_PHYSICAL_ADDR` macro is defined in the [arch/x86/include/asm/boot.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/boot.h) header file and it looks like this:
```C ```C
#define LOAD_PHYSICAL_ADDR ((CONFIG_PHYSICAL_START \ #define LOAD_PHYSICAL_ADDR ((CONFIG_PHYSICAL_START \
@ -337,7 +337,7 @@ Remember that value of the `ebp` register is the physical address of the `startu
& ~(CONFIG_PHYSICAL_ALIGN - 1)) & ~(CONFIG_PHYSICAL_ALIGN - 1))
``` ```
As we can see it just expands to the aligned `CONFIG_PHYSICAL_ALIGN` value which represents the physical address of where to load the kernel. After comparison of the `LOAD_PHYSICAL_ADDR` and value of the `ebx` register, we add offset from the `startup_32` where to decompress the compressed kernel image. If the `CONFIG_RELOCATABLE` option is not enabled during kernel configuration, we just put default address where to load kernel and add `z_extract_offset` to it. As we can see it just expands to the aligned `CONFIG_PHYSICAL_ALIGN` value which represents the physical address of where to load the kernel. After comparison of the `LOAD_PHYSICAL_ADDR` and value of the `ebx` register, we add the offset from the `startup_32` where to decompress the compressed kernel image. If the `CONFIG_RELOCATABLE` option is not enabled during kernel configuration, we just put the default address where to load kernel and add `z_extract_offset` to it.
After all of these calculations we will have `ebp` which contains the address where we loaded it and `ebx` set to the address of where kernel will be moved after decompression. After all of these calculations we will have `ebp` which contains the address where we loaded it and `ebx` set to the address of where kernel will be moved after decompression.

1
contributors.md
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@ -91,3 +91,4 @@ Thank you to all contributors:
* [Mack Stump](https://github.com/rmbreak) * [Mack Stump](https://github.com/rmbreak)
* [Pushpinder Singh](https://github.com/PrinceDhaliwal) * [Pushpinder Singh](https://github.com/PrinceDhaliwal)
* [Xiaoqin Hu](https://github.com/huxq) * [Xiaoqin Hu](https://github.com/huxq)
* [Jeremy Cline](https://github.com/jeremycline)