Re: [PATCH v2] arch/riscv: Enable kprobes when CONFIG_MODULES=n

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Sun Mar 24, 2024 at 1:29 AM EET, Jarkko Sakkinen wrote:
> Tracing with kprobes while running a monolithic kernel is currently
> impossible due the kernel module allocator dependency.
>
> Address the issue by allowing architectures to implement module_alloc()
> and module_memfree() independent of the module subsystem. An arch tree
> can signal this by setting HAVE_KPROBES_ALLOC in its Kconfig file.
>
> Realize the feature on RISC-V by separating allocator to module_alloc.c
> and implementing module_memfree().
>
> Link: https://www.sochub.fi # for power on testing new SoC's with a minimal stack
> Link: https://lore.kernel.org/all/20220608000014.3054333-1-jarkko@profian.com/ # continuation
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

As for testing I tried the kprobes example for boottime tracing
dcoumentation:

https://www.kernel.org/doc/html/v5.7/trace/boottime-trace.html

I.e.

ftrace.event {
	kprobes.vfs_read {
		probes = "vfs_read $arg1 $arg2"
		filter = "common_pid < 100"
		enable
	}
}

kernel {
	console = hvc0
	earlycon = sbi
	trace_options = sym-addr
	trace_event = "initcall:*"
	tp_printk
	dump_on_oops = 2
	trace_buf_size = 1M
}

BR, Jarkko