From: Mark Rutland > Sent: 09 January 2023 13:58 > > This series adds a new DYNAMIC_FTRACE_WITH_CALL_OPS mechanism, and > enables support for this on arm64. This significantly reduces the > overhead of tracing when a callsite/tracee has a single associated > tracer, avoids a number of issues that make it undesireably and > infeasible to use dynamically-allocated trampolines (e.g. branch range > limitations), and makes it possible to implement support for > DYNAMIC_FTRACE_WITH_DIRECT_CALLS in future. > > The main idea is to give each ftrace callsite an associated pointer to > an ftrace_ops. The architecture's ftrace_caller trampoline can recover > the ops pointer and invoke ops->func from this without needing to use > ftrace_ops_list_func, which has to iterate through all registered ops. > > To do this, we use -fpatchable-function-entry=M,N, there N NOPs are > placed before the function entry point... Doesn't this bump the minimum gcc version up to something like 9.0 ? How does it interact with the 'CFI stuff' that also uses the same area? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
