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fix boot-4

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Alexander Kuleshov 2018-04-04 00:20:22 +06:00
parent 4382670c38
commit e735b508d1
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1 changed files with 12 additions and 8 deletions
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Booting/linux-bootstrap-4.md
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@ -151,7 +151,7 @@ Bit 6 (write): KEEP_SEGMENTS
So, if the `KEEP_SEGMENTS` bit is not set in the `loadflags`, we need to set `ds`, `ss` and `es` segment registers to the index of data segment with base `0`. That we do: So, if the `KEEP_SEGMENTS` bit is not set in the `loadflags`, we need to set `ds`, `ss` and `es` segment registers to the index of data segment with base `0`. That we do:
```C ```C
testb $(1 << 6), BP_loadflags(%esi) testb $KEEP_SEGMENTS, BP_loadflags(%esi)
jnz 1f jnz 1f
cli cli
@ -337,8 +337,6 @@ When we are using position-independent code an address is obtained by adding the
jge 1f jge 1f
#endif #endif
movl $LOAD_PHYSICAL_ADDR, %ebx movl $LOAD_PHYSICAL_ADDR, %ebx
1:
addl $z_extract_offset, %ebx
``` ```
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/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/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/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/include/asm/boot.h) header file and it looks like this:
@ -354,6 +352,7 @@ As we can see it just expands to the aligned `CONFIG_PHYSICAL_ALIGN` value which
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. But that is not the end. The compressed kernel image should be moved to the end of the decompression buffer to simplify calculations where kernel will be located later. For this: 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. But that is not the end. The compressed kernel image should be moved to the end of the decompression buffer to simplify calculations where kernel will be located later. For this:
```assembly ```assembly
1:
movl BP_init_size(%esi), %eax movl BP_init_size(%esi), %eax
subl $_end, %eax subl $_end, %eax
addl %eax, %ebx addl %eax, %ebx
@ -377,6 +376,11 @@ To understand the magic with `gdt` offsets we need to look at the definition of
```assembly ```assembly
.data .data
gdt64:
.word gdt_end - gdt
.long 0
.word 0
.quad 0
gdt: gdt:
.word gdt_end - gdt .word gdt_end - gdt
.long gdt .long gdt