I would like to provide a facility to create wrapper functions without lots of argument shuffling. To achieve that, the wrapping function and the wrapped function should have the same prototype. There will be a trampoline that puts additional data somewhere (possibly including the address of the wrapped function, but that interpretation is up to the wrapping function) and then transfers control to the wrapper function with an indirect jump (tail call).
For signal safety, I think the hidden argument needs to be in a register (instead of, say, thread-local storage). Most System V ABI variants seem to reserve a register for use by the dynamic linker, or for the static chain pointer of nested functions. Is there a way to reuse either register for this purpose and assign it to a local variable reliably at the start of the wrapper function implementation? Thanks, Florian
