Re: [PATCH 2/2] x86, boot: Optimize the elf header handling.

From: Eric W. Biederman
Date: Sun Jul 01 2012 - 14:25:59 EST

"H. Peter Anvin" <hpa@xxxxxxxxx> writes:

> On 07/01/2012 10:09 AM, Eric W. Biederman wrote:
>> I am suspecting something similar. At the moment I am trying
>> to remember how to get early printk working in misc.c so I can
>> poke around a bit more.
>> The theory that I was working on, that used to be true, and
>> seems to be true of everything except the percpu section is
>> that objcopy just does the right thing when creating vmlinux.bin.
>> vmlinux.bin being what we compress.
>> I don't see anything obviously wrong with the headers of vmlinux.bin
>> although we still unnecessarily have section headers in that file.
> We leave the section headers in for the benefit of Xen IIRC.

Well I see what is going on now.

In the vmlinux the paddrs and the poffsests stop tracking when they
come to the percpu PT_LOAD segment.

It looks like we give the percpu segment a 4K alignment in memory
and a 2M alignment in the file.

It looks like something is causing ld to compute an unfortunate physical
load address for the percpu section.

At first glace I would say that is a bug. Either we need the alignment
or we don't. But if we need the alignment we certainly need it to
be respected for the real memory locations of the init symbols..



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