Adding new section to core file

Adding new section to core file

[vaibhav sinha]

Hi

As I understand, core files are also in ELF format. I want to add a
new section to the core file. I know how to do that for an executable
using objcopy, as shown below:

$ echo 'int main() { puts ("Hello world"); }' | gcc -x c - -c -o hello.o

$ echo "this is my special data" >mydata

$ objcopy --add-section .mydata=mydata \
          --set-section-flags .mydata=noload,readonly hello.o hello2.o

$ gcc hello2.o -o hello

$ ./hello
Hello world

$ objdump -sj .mydata hello

hello:     file format elf32-i386

Contents of section .mydata:
 0000 74686973 20697320 6d792073 70656369  this is my speci
 0010 616c2064 6174610a                    al data.




But when I try the same for a core file, I get warnings such as


BFD: newcorefile5: warning: allocated section `load2' not in segment

BFD: newcorefile5: warning: allocated section `load4' not in segment

BFD: newcorefile5: warning: allocated section `load5' not in segment

BFD: newcorefile5: warning: allocated section `load8' not in segment

BFD: newcorefile5: warning: allocated section `load9' not in segment

BFD: newcorefile5: warning: allocated section `load10' not in segment

BFD: newcorefile5: warning: allocated section `load13' not in segment

BFD: newcorefile5: warning: allocated section `load14' not in segment

BFD: newcorefile5: warning: allocated section `load17' not in segment

BFD: newcorefile5: warning: allocated section `load20' not in segment

BFD: newcorefile5: warning: allocated section `load21' not in segment

BFD: newcorefile5: warning: allocated section `load22' not in segment

BFD: newcorefile5: warning: allocated section `load23' not in segment

BFD: newcorefile5: warning: allocated section `load24' not in segment

BFD: newcorefile5: warning: allocated section `load25' not in segment

BFD: newcorefile5: warning: allocated section `load26' not in segment



Using objdump I cant find the new section that I added.

Can someone please help me with adding a new section to core file in a
similar manner as we add it to an executable.


Regards

Vaibhav

Re: Adding new section to core file

[Alan Modra]

On Mon, Apr 06, 2015 at 07:00:00PM +0530, vaibhav sinha wrote:
> As I understand, core files are also in ELF format. I want to add a
> new section to the core file. I know how to do that for an executable
> using objcopy, as shown below:

But, you didn't "do that for an executable".  You added the extra
section to a relocatable object file.  That is very different from
adding a section to an executable (or core file).  Generally, you
can't successfully change executables using objcopy in ways that
require addresses to change.

-- 
Alan Modra
Australia Development Lab, IBM