Re: [PATCH v4 3/3] selftests: livepatch: test livepatching a kprobed function

[Miroslav Benes]

Hi,

On Mon, 30 Sep 2024, Michael Vetter wrote:

> The test proves that a function that is being kprobed and uses a
> post_handler cannot be livepatched.
> 
> Only one ftrace_ops with FTRACE_OPS_FL_IPMODIFY set may be registered
> to any given function at a time.
> 
> Signed-off-by: Michael Vetter <mvetter@xxxxxxxx>

since my memory is short, I wondered why you need a separate module to 
register a kprobe for cmdline_proc_show() in vmlinux and why it cannot be 
achieved through tracefs. So... the test ensures that 
FTRACE_OPS_FL_IPMODIFY is exclusive. A kprobe sets FTRACE_OPS_FL_IPMODIFY 
flag if and only if post_handler is not NULL which also indicates a 
situation when regs->ip may be changed in that kprobe. This is something 
which cannot be done in tracefs and hence the module.

It was not clear to me from the changelog.

Miroslav