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Re: relocation entries for absolute symbols

From: Vivek Goyal
Subject: Re: relocation entries for absolute symbols
Date: Wed, 12 Jul 2006 22:44:44 -0400
User-agent: Mutt/1.5.11

On Mon, Jun 26, 2006 at 03:20:53PM -0700, Ian Lance Taylor wrote:
> Amit Gud <address@hidden> writes:
> > I'm compiling the GNU/Linux kernel as a shared library and I've found
> > that relocation entries are created even for absolute symbols. Is
> > there any work-around for this, or is it a known bug?
> That is correct behaviour if the symbol is globally visible.  In a
> shared library, by default, any symbol may be overridden by the main
> executable.  That means that a relocation entry is required.

I am compiling my kernel with option --pic-executable to ld. As per ld
man page, symbols defined in the executable can not be overriden. Still
I see the relocation entries of type R_386_32 for absolute symbols. 

c0100018  00003e01 R_386_32          c0412000   __bss_start
c010001d  00003601 R_386_32          c04d7768   __bss_stop
c0100064  00004901 R_386_32          c04d8000   pg0
c0100848  00004501 R_386_32          c03dc040   jiffies

If absolute symbols are not to be relocated then why is linker generating
relocation entries.

Then I used options "--pic-executable -Bsymbolic". In this case
also linker generated relocation entries for absolute sysmbols. Only
difference was that relocation type was R_386_RELATIVE and linker
had already processed the relocations for absolute sysmbols. 

c0100018  00000008 R_386_RELATIVE

Addr c0100018 belongs to absolute symbol referece (_bss_start) in code. 

In this case if absolute symbols relocation have already been processed
and absolute symbols have no more to be relocated then why
a R_386_RELATIVE entry is being generated.

My basic goal is to build dynamically relocatable kernel. I thought that
I can use the relocation information and relocate the kernel. But the
relocation entries generated for absolute symbols as shown above spoil
the whole approach.

Is it a bug? or expected behaviour?


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