Re: How to list all symbolic names for references to global varibables and functions with objdump (for MIPS arch)?

[Nick Clifton <nickc at redhat dot com>]

Hi Pan,

> Support for .init sections means the kernel allocates pages from the
> init sections when the programs are loaded and being initialized. And
> after initialization is finished, the kernel reclaims the pages for
> init sections. This can reduce memory requirements significantly for
> an embedded system.

Ah - OK - I understand now.  It sounds like what you really want to do 
is to hook into the linker's section-garbage-collection mechanism.  This 
currently allows the linker to find functions which are never used and 
throw them away, (providing that the program has been compiled with 
gcc's -ffunction-section command line option).

What you want to do is to augment the current code so that any function 
which is used by which is not referenced via the program's entry 
point(*) is placed into a special segment which the loader knows it can 
discard after the initialization routines have been run.

Cheers
  Nick

(*) Actually you will also have to consider termination routines as well 
(C++ deconstructors, .fini sections etc).  These may also invoke 
functions in the program which are not referenced via the entry point, 
but which need to be present when the program exits.  Possibly your 
kernel will have to reload the segment containing the init routines. 
Although if the program is exiting because it has run out of memory this 
might prove difficult to implement...


You know it might be a whole lot easier to abandon trying to make this 
an automatic mechanism and instead require that the program's creator 
annotate any only-used-during-init functions via some kind of attribute.
Eg if you specified that any such function had to be given a section 
name attribute of .init.text say, then you could arrange for your linker 
script to keep all code in this section separate from the normal .text 
section and then your kernel could know to discard this section once it 
is ready to invoke the program's entry point.