x86/kernel/head_32.S

[孙建希]

hello,

arch/x86/kernel/head_32.S:

#define pa(X) ((X) - __PAGE_OFFSET)

__HEAD  ENTRY(startup_32)  + movl pa(stack_start),%ecx...
+ movl %eax,%ss  2:  + leal -__PAGE_OFFSET(%ecx),%esp

I am confused by `leal -__PAGE_OFFSET(%ecx),%esp`.
`pa(stack_start)` have convert `stack_start` to physicall address.
why we need `-__PAGE_OFFSET(%ecx)` instead of `%ecx`?


I have found the commit in github:

https://github.com/torvalds/linux/commit/11d4c3f9b671720e80353dd7e433ff2bf65e9500#diff-3910cf85e24534430413b7133160d0ba
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