netdev - Re: [PATCH bpf-next] samples/bpf: fix kprobe attachment issue on x64

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Date:   Sun, 29 Apr 2018 17:06:24 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     ast@...com, daniel@...earbox.net, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH bpf-next] samples/bpf: fix kprobe attachment issue on x64

On Sun, Apr 29, 2018 at 05:00:23PM -0700, Yonghong Song wrote:
> 
> 
> On 4/29/18 4:20 PM, Alexei Starovoitov wrote:
> > On Sun, Apr 29, 2018 at 03:06:31PM -0700, Yonghong Song wrote:
> > > Commit d5a00528b58c ("syscalls/core, syscalls/x86: Rename
> > > struct pt_regs-based sys_*() to __x64_sys_*()") renamed a lot
> > > of syscall function sys_*() to __x64_sys_*().
> > > This caused several kprobe based samples/bpf tests failing.
> > > 
> > > This patch fixed the problem by using __x64_sys_*(),
> > > instead of sys_*(), in bpf program SEC annotations if
> > > the target arch is __TARGET_ARCH_x86.
> > > 
> > > Fixes: d5a00528b58c ("syscalls/core, syscalls/x86: Rename struct pt_regs-based sys_*() to __x64_sys_*()")
> > > Signed-off-by: Yonghong Song <yhs@...com>
> > > ---
> > >   samples/bpf/map_perf_test_kern.c                  | 32 +++++++++++++++++++++++
> > >   samples/bpf/test_current_task_under_cgroup_kern.c |  4 +++
> > >   samples/bpf/test_map_in_map_kern.c                |  4 +++
> > >   samples/bpf/test_probe_write_user_kern.c          |  4 +++
> > >   samples/bpf/trace_output_kern.c                   |  4 +++
> > >   samples/bpf/tracex2_kern.c                        |  4 +++
> > >   6 files changed, 52 insertions(+)
> > > 
> > > diff --git a/samples/bpf/map_perf_test_kern.c b/samples/bpf/map_perf_test_kern.c
> > > index 2b2ffb9..79f4320 100644
> > > --- a/samples/bpf/map_perf_test_kern.c
> > > +++ b/samples/bpf/map_perf_test_kern.c
> > > @@ -95,7 +95,11 @@ struct bpf_map_def SEC("maps") lru_hash_lookup_map = {
> > >   	.max_entries = MAX_ENTRIES,
> > >   };
> > > +#ifdef __TARGET_ARCH_x86
> > > +SEC("kprobe/__x64_sys_getuid")
> > > +#else
> > >   SEC("kprobe/sys_getuid")
> > > +#endif
> > 
> > I think it would be better to hack bpf_load.c to add __x64_
> > automatically when it matches "sys_" in the beginning of kprobe name.
> 
> I thought this before but there a few outliers for the particular
> kernel configuration I have for latest bpf-next:
> 
> drivers/video/fbdev/core/sysfillrect.c:
>   void sys_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
> drivers/video/fbdev/core/syscopyarea.c:
>   void sys_copyarea(struct fb_info *p, const struct fb_copyarea *area)
> drivers/video/fbdev/core/sysimgblt.c:
>   void sys_imageblit(struct fb_info *p, const struct fb_image *image)
> 
> I am not sure whether any other outliers for other configurations or
> in the future somebody could introduces a kernel function sys_ but
> not a syscall.

How about trying to kprobe both ?
First __x64_sys_* and if it doesn't exist kprobe on sys_* ?