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My Own Private Binary: An Idiosyncratic Introduction to Linux Kernel Modules
Several years ago, I spent a serious chunk of time figuring out how to make really teensy ELF executable files. I started down this path because I was annoyed that all of my programs, no matter how short they were, never got smaller than 4k or so.
One of the fields of the linux_binprm struct is the filename, so we examine it, and if there's no ".com" extension, then we return negative ENOEXEC, the errno equivalent to our "Exec format error" message. (If for whatever reason you don't trust your compiler to properly handle Unicode characters, you can instead assume a UTF-8 environment and write the second argument to strcmp() as".\342\231\232".) So you could in theory potentially maybe argue that, just for example, using the character immediately preceding the extension would also be valid metadata, and that could be defined to specify optional behavior, like the default stack value for example …
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