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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