Date: Sun, 20 Apr 2008 23:24:32 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: ertr1013@student.uu.se Cc: emily.bckr@gmail.com, freebsd-hackers@freebsd.org Subject: Re: symbol table Message-ID: <20080420.232432.-1175574853.imp@bsdimp.com> In-Reply-To: <20080420103910.GA92852@owl.midgard.homeip.net> References: <5124a9390804200202h535112dcx4005e9df6e5e0f5e@mail.gmail.com> <20080420103910.GA92852@owl.midgard.homeip.net>
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In message: <20080420103910.GA92852@owl.midgard.homeip.net>
Erik Trulsson <ertr1013@student.uu.se> writes:
: On Sun, Apr 20, 2008 at 12:02:09PM +0300, emily becker wrote:
: > Hi,
: >
: > I have a question about symbol table.
: > One of the section In symbol table is memory adress which symbol is located.
: > I wonder if this memory adress is bound at run-time or compile-time?
:
: It depends. Symbols referring to objects in a dynamically loaded library
: will be bound at run-time, the rest should be bound at compile-time.
They are bound at link-time, not compile-time. This is splitting a
fine hair, but compile-time is when a .o or .so is created, while link
time combines .o-like things together into a bigger thing. When that
bigger thing is a final link, the addresses for the static portions of
the binary are set. When the final thing is a dynamic library, the
addresses float (since all the code is PIC anyway, they don't really
matter). Dynamic parts of executables are bound at run-time.
: > if it is compile-time, I don't understand how do we know whether the symbol
: > is located this adress.
: > Maybe this adress is already bound by other process or like this.
:
: Each process runs in its own address space, and therefore the compiler
: (actually: the linker) can know exactly where in this address space things
: will end up.
The run-time linker (ld.so) is the one that knows where things wind up
in a given process... libc.so and other shared libraries can and do
link at different addresses for different processes.
Warner
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