DevConf.US 2019

While ELF is an old standard it has enabled the development of remarkable tools and the Linux Kernel's objtool scanner is a great example of this. Objtool has evolved over time from a stack checker to enabling such kernel features as reliable, super-low overhead stack tracing, live patching, and more. Recently checks for Spectre/Meltdown mitigation and other useful checks have also been incorporated. Objtool achieves these feats by scanning the object files produced by the compiler, checking code patterns, and collecting information that the kernel uses at runtime to implement these features. We'll go into detail on how objtool does this and, finally, we'll discuss ongoing work incorporating other kernel build-time scanning tools into objtool.