Re: [PATCH] bpf: mark get_entry_ip as __maybe_unused

[Daniel Borkmann]

On 11/3/22 4:32 PM, Jonas Rabenstein wrote:
> Hi again,
> after sending this out, I noticed this is only a problem in the stable
> versions (starting from v6.0.3), as c09eb2e578eb1668bbc has been applied (as
> 03f148c159a250dd454) but not 0e253f7e558a3e250902 ("bpf: Return value in kprobe
> get_func_ip only for entry address") which makes always use of get_entry_ip.
> I therefore think, 0e253f7e558a3e250902 needs to be added to the stable v6.0
> series as well as otherwise it can't be compiled with -Werror if
> CONFIG_X6_KERNEL_IBT is set but CONFIG_FPROBE isn't.

Thanks for the info, Jonas. Added Greg wrt stable cherry-pick.

> On Thu, Nov 03, 2022 at 04:03:03PM +0100, Jonas Rabenstein wrote:
> > Commit c09eb2e578eb1668bbc ("bpf: Adjust kprobe_multi entry_ip
> > for CONFIG_X86_KERNEL_IBT") introduced the get_entry_ip() function.
> > Depending on CONFIG_X86_KERNEL_IBT it is a static function or only
> > a macro definition. The only user of this symbol so far is in
> > kprobe_multi_link_handler() if CONFIG_FPROBE is enabled.
> > If CONFIG_FROBE is not set, the symbol is not used and - depending
> > on CONFIG_X86_KERNEL_IBT - a warning for get_entry_ip() is emitted.
> > To solve this, the function should be marked as __maybe_unused.
> >
> > Signed-off-by: Jonas Rabenstein <rabenstein@xxxxxxxxx>
> > ---
> >   kernel/trace/bpf_trace.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index f2d8d070d024..19131aae0bc3 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1032,7 +1032,7 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_tracing = {
> >   };
> >   
> >   #ifdef CONFIG_X86_KERNEL_IBT
> > -static unsigned long get_entry_ip(unsigned long fentry_ip)
> > +static unsigned long __maybe_unused get_entry_ip(unsigned long fentry_ip)
> >   {
> >   	u32 instr;
> >   
> > --
> > 2.37.4