Our source file contains only 2 functions, add5 and add10, which adds 5 or 10 respectively to the only input parameter. A simple toy object fileįor the purposes of this article, let's create a simple toy object file, so we can use it in our experiments: Malware analysis, code from a different operating system etc - all these scenarios may put us in a position, where either linking is not possible or the runtime environment is not suitable.
#LUXCORERENDER FILE OBJ FULL#
Maybe we have a source file, but cannot create a full featured executable, because of the missing build time or runtime dependencies. Or we have a piece of a rare, obscure program and we can't link to it, because it was compiled with a rare, obscure compiler.
#LUXCORERENDER FILE OBJ DRIVER#
Perhaps we're writing an open-source replacement for a proprietary Linux driver or an application, and want to compare if the behaviour of some code is the same. Why would we want to execute an object file? So, in this series of blog posts we will investigate if it is possible to execute machine code directly from object files skipping all the later steps.
One interesting thing to note about this overall process is that we get the executable machine code directly from step 1 (compiling the source code), but if any of the later steps fail, we still can't execute our program. This process is called runtime linking: when our executable is being started, the operating system will invoke the dynamic loader, which should find all the needed libraries, copy/map their code into our target process address space, and resolve all the dependencies our code has on them. Instead it expects to "borrow" part of the code at runtime from shared libraries for some of its functionality: These days, most executables on Linux are dynamically linked: the executable itself does not have all the code it needs to run a program. However, at this point, our executable might still be incomplete. The output of the linker is usually our target executable, so only one file. The next step is the linker: since the code in different object files may reference each other, the linker is responsible for assembling all these object files into one big program and binding these references together. If the project contains multiple source files, we usually get as many object files. The output of the compiler is a number of object files. When we write software using a high-level compiled programming language, there are usually a number of steps involved in transforming our source code into the final executable binary:įirst, our source files are compiled by a compiler translating the high-level programming language into machine code. Calling a simple function without linking
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