Re: [PATCHv2 RFC bpf-next 0/7] bpf: Add support for ftrace probe

On Mon, 19 Apr 2021 22:51:46 +0200
Jiri Olsa [off-list ref] wrote:

now, it looks like the fgraph_ops entry callback does not have access
to registers.. once we have that, we could store arguments for the exit
callback and have all in place.. could this be added? ;-)

Sure. The only problem is that we need to do this carefully to not break
all the architectures that support function graph tracing.

For function tracing, I usually add "CONFIG_HAVE_..." configs that state if
the architecture supports some ftrace feature, and if it does it can use a
different callback prototype. But it does get messy.

Ideally, I would love to go and update all architectures to support all
features, but that requires understanding the assembly of all those
architectures :-p

To test that I don't break other archs, I usually just support x86_64 and
leave x86_32 behind. I mean, who cares about x86_32 anymore ;-)

-- Steve