printf() only supports 7 arguments

[danobi]

Is your feature request related to a problem? Please describe.

It would be useful to have support for more arguments. I don't think there's a technical limit.

Describe the solution you'd like

More args

Describe alternative solutions or features you've considered

n/a

[danobi]

One way I thought of to support arbitrary number of arguments is to:

• use a format string regex (see bpftrace::verify_format_string) to capture and pull out all format string tokens
• format each token one by one in scratch buffer
• add formatted string to accumulator, being careful to truncate if accumulated length goes past max size
• add interposed text (ie not format string token) as appropriate, still being careful to truncate

The reason we can't do it all in one shot is b/c *printf family of functions need a fixed # of args known at compile time (b/c of the va_args) stuff. Same thing w/ c++ parameter packs and if we wanted to use fmt (https://fmt.dev/latest/api.html#printf-formatting) + parameter packs

[Birch-san]

*printf family of functions need a fixed # of args known at compile time

Can we use *vprintf instead?

[danobi]

Can we use *vprintf instead?

I looked into this but there's no way to safely construct a va_list struct (according to the internet)