On 28/08/2024 10:36, Vegard Nossum wrote:
In order to give assembly code access to C structs without having to hardcore member offsets, the kernel compiles a C source file listing all the structs and offsets that are needed in assembly code. Using some C preprocessor trickery and a sed script, the compiled assembly code is turned back into C preprocessor code that in turn can be used by the asssembly code. This sed script is very hard to read and understand. Remove the sed script and compile the C source listing structs and offsets to an object file (instead of assembly code) that embeds C source directly. Then extract the C source using objcopy. The resulting code is more readable, less fragile, and sligthly shorter. Note to reviewers: The 'objcopy ... /dev/stdout | cat' bit is needed to force the correct ordering of the objcopy lines vs. the surrounding echo commands; without it, objcopy will open /dev/stdout (which refers to a temporary file created by kbuild) and reset the file offset to 0. In other words, the pipe ensures that objcopy doesn't overwrite the lines that already exist in /dev/stdout.
Turns out LLVM's objcopy doesn't support writing to /dev/stdout, so we might have to use a temporary file. I'll look into it and send a v2. Vegard
