CODEWITHSUNDEEP
linux-kernelx86bootloader
Amit Singh Tomar
Amit Singh Tomar

Reputation: 8610

Confused from x86 memory Layout of kernel loader

I am new to Linux kernel stuff and is reading about memory layout of Kernel loader but confused with below given diagram

0A0000  +------------------------+
        |  Reserved for BIOS     |  Do not use.  Reserved for BIOS EBDA.
09A000  +------------------------+
        |  Command line          |
        |  Stack/heap            |  For use by the kernel real-mode code.
098000  +------------------------+  
        |  Kernel setup          |  The kernel real-mode code.
090200  +------------------------+
        |  Kernel boot sector    |  The kernel legacy boot sector.
090000  +------------------------+
        |  Protected-mode kernel |  The bulk of the kernel image.
010000  +------------------------+
        |  Boot loader           |  <- Boot sector entry point 0000:7C00
001000  +------------------------+
        |  Reserved for MBR/BIOS |
000800  +------------------------+
        |  Typically used by MBR |
000600  +------------------------+ 
        |  BIOS use only         |

Now statement explaining this diagram is bit confusing for me.

When using bzImage, the protected-mode kernel was relocated to 0x100000 ("high memory"), and the kernel real-mode block (boot sector,setup, and stack/heap) was made relocatable to any address between 0x10000 and end of low memory.

Now first thing where is 0x100000 address is in above diagram ??

Second thing is when its says kernel real-mode block was made relocatable to "any address between 0x10000 and end of low memory" means it was relocatable to address between 0x10000 to 000600?

Intially kernle mode block is placed between 0x10000 to 09A000.

"it is desirable to keep the "memory ceiling" -- the highest point in low memory touched by the boot loader -- as low as possible, since some newer BIOSes have begun to allocate some rather large amounts of memory, called the Extended BIOS Data Area, near the top of low memory".

when its says low memory means memory downside towards 000600 and high memory upside towards 0A0000??

Upvotes: 0

Views: 965

Answers (1)

Alexey Frunze
Alexey Frunze

Reputation: 62106

Now first thing where is 0x100000 address is in above diagram ??

0x100000 is not on the diagram because only the first megabyte is special. Beyond that point the physical memory is contiguous at least until the 15-16MB point.

Second thing is when its says kernel real-mode block was made relocatable to "any address between 0x10000 and end of low memory" means it was relocatable to address between 0x10000 to 000600?

Real-mode code can live anywhere below approximately 1 MB and the end is probably around there, at 0x9A000 or wherever the EBDA begins.

when its says low memory means memory downside towards 000600 and high memory upside towards 0A0000??

You have it on the diagram, from 0xA0000 downwards, towards 0.

Upvotes: 1

Related Questions