[PATCH] kexec based hibernation: a prototype of kexec multi-stage load
ying.huang at intel.com
Thu May 15 00:57:53 EDT 2008
On Wed, 2008-05-14 at 14:43 -0700, Eric W. Biederman wrote:
> Then as a preliminary design let's plan on this.
> - Pass the rentry point as the return address (using the C ABI).
> We may want to load the stack pointer etc so we can act as
> a direct entry point for new code.
There are some issues about passing entry point as return address. The
kexec jump (or kexec with return) is used for
- Switching between original kernel (A) and kexeced kernel (B)
- Call some code (such as BIOS code) in physical mode
1) When call some code in physical mode, the called code can use a
simple return to return to kernel A. So there is no return address on
stack after return to kernel A. Instead, argument 1 is on stack top.
2) When switch back from kernel B to kernel A, kernel B will call the
jump back entry of kernel A with C ABI. So, the return address is on
stack top. And kernel A get jump back entry of kernel B via the return
Because the stack state is different between 1) and 2), the jump back
entry of kernel A should distinguish them. Possible solution can be as
a) Before kernel A call some physical mode code or kernel B, it set
argument 1 to be a magic number that can not be return address (such as
-1). Jump back entry of kernel A can check whether the stack top is
argument 1 or return address.
b) Distinguish by return address. Such as, called physical mode code
must return 0, while kernel B must set %eax to some other number.
c) Use different entry point for 1) and 2). Two entry points are deduced
from return address. Such as:
entry1 = return_address;
entry2 = return_address & ~0xfff; /* page aligned */
entry1 is used by physical mode code. entry2 is used by kernel B.
Which one is better? Or some other solution?
More information about the kexec