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POLoading ELF shared library and custom binfmt executable into same Linux address space
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  1. POLoading ELF shared library and custom binfmt executable into same Linux address space
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    copied!<p>I am working on a project to load and run a custom binary format executable (PE, in my case) on a Linux platform. I've done this pretty successfully so far by first loading the executable and then loading a small ELF shared library that calls the start address of the executable and then exits safely.</p> <p>I would really like not doing the ELF loading myself for a few reasons, though. First, the shared library I use is written in assembly (I can't use anything else because I'm not linking to <code>libc</code>, etc.), which will be very platform-specific, and I'd like to move away from that and use C so I can compile for any platform. Also, it will be easier and safer to use Linux's native ELF loader instead of my own simplified version.</p> <p>I'm wondering if there is a way to use my binfmt handler, an installed kernel module, to load my executable and <em>then</em> ask Linux to load my shared library (and its dependencies) into the same address space without overwriting my executable code. I first thought that the <code>uselib</code> syscall might be useful, but the description on the man page is unclear about whether or not this will serve my purposes:</p> <blockquote> <p>From libc 4.4.4 on only the library "/lib/ld.so" is loaded, so that this dynamic library can load the remaining libraries needed (again using this call). This is also the state of affairs in libc5.</p> <p>glibc2 does not use this call.</p> </blockquote> <p>I've also never seen an example of its use, and I'm always wary of using syscalls that I don't understand.</p> <p>Is there a good way to achieve what I've described? Can I use Linux's existing capabilities to load a shared library (written in C) into an address space already containing executable code, and, if so, how can I use that library without knowing where it has been loaded?</p>
 

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