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Message-ID: <3faf05680603181422y7447fd7duc1032bd0e07b9c68@mail.gmail.com>
Date: Sun, 19 Mar 2006 03:52:17 +0530
From: "vamsi krishna" <vamsi.krishnak@gmail.com>
To: linux-kernel@vger.kernel.org
Subject: Idea to create a elf executable from running program [process2executable]
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Hello All,

I have been working on an idea of creating an executable from a
running process image.

MOTIVATION:
Process migration among the nodes in distributed computing,
checkpointing process state.

BASIS:

The basis of my idea would be update the existing executable with
extra PHDRS (Program Headers) with type PT_LOAD and each of these
headers corresponding the vaddr mapping from /proc/<pid>/maps.

I have done some basic study of kernels loders code in
'fs/binfmt_elf.c' especially code in 'load_elf_binary' function, the
following is my understanding.
<------------------------------------------>
bss=0;
brk=0;
foreach (phdr in elf_header){

   if(phdr->type == PT_LOAD){
        if( phdr->filesize < phdr->memsize){
           /* Segment with .bss, so update brk and bss*/
        }
       else {
          /* Just map it*/
       }
    }
/*Update brk bss*/
}
<------------------------------------>

from the above the kernel is updating brk, thus creating the start of
sbrk(0) only when it sees a  PT_LOAD segment with filesize<memsize. So
if I create a elf executable with all PT_LOAD segments with out any
segments with filesize < memsize. The kernel will set brk base i.e
sbrk(0) to the value phdr->vaddr+phdr->memsize of the last PT_LOAD
segment its mapping? so do I need to reoder my PT_LOAD segments so
that the heap goes as the last PT_LOAD segment?

Is there any way we can tell the elf loader to force the vaddr for
sbrk(0) i.e brk base ?

Let me know your suggestion on this idea?

Really appreciate your valuable comments.

Sincerely,
Vamsi

[PS: I dont know if some one has already implemented this idea??]
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