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Re: Where in GRUB2 source code is the handover/jump to kernel code on x8
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From: |
Colin Watson |
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Subject: |
Re: Where in GRUB2 source code is the handover/jump to kernel code on x86? |
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Date: |
Thu, 3 Sep 2015 18:24:36 +0100 |
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User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, Sep 03, 2015 at 02:49:45PM +0200, address@hidden wrote:
> <html><head></head><body><div style="font-family: Verdana;font-size:
> 12.0px;"><div>
Plain-text mail would be appreciated, or at least mail with a text/plain
part.
> I'm looking for the line of code where GRUB2 finally jumps to kernel
> code and thus hands over execution on x86 systems? I guess it's in an
> assembler file since this is very low architecture stuff. I looked at
> the source files in /grub-core/boot/i386/pc/*.S and found a JMP in
> boot.S at line 455 but kernel_address could be the address of the
> GRUB2 kernel in memory and not the linux kernel.
grub_linux_boot is the top level of this. From there it gets
complicated. On x86, it goes from there to grub_relocator32_boot, which
(essentially) copies the code from grub-core/lib/i386/relocator32.S into
a freshly-allocated area of memory and fills in some details specific to
the kernel image it wants to boot. The final bit is:
.byte 0xea
VARIABLE(grub_relocator32_eip)
.long 0
This is a JMP opcode followed by space into which the relocator fills in
an instruction pointer. When that's put together, it forms the line of
code you're looking for.
--
Colin Watson address@hidden