[PATCH net-next] bpf/tracing: fix kernel/events/core.c compilation error

[PATCH net-next] bpf/tracing: fix kernel/events/core.c compilation error

[Yonghong Song]

Commit f371b304f12e ("bpf/tracing: allow user space to
query prog array on the same tp") introduced a perf
ioctl command to query prog array attached to the
same perf tracepoint. The commit introduced a
compilation error when either CONFIG_BPF_SYSCALL or
CONFIG_EVENT_TRACING is not defined:
  kernel/events/core.o: In function `perf_ioctl':
  core.c:(.text+0x98c4): undefined reference to `bpf_event_query_prog_array'

This patch fixed this error.

Fixes: f371b304f12e ("bpf/tracing: allow user space to query prog array on the same tp")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 include/linux/bpf.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 93e15b9..8dbbfd7 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -254,7 +254,6 @@ typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,
 
 u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
 		     void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy);
-int bpf_event_query_prog_array(struct perf_event *event, void __user *info);
 
 int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 			  union bpf_attr __user *uattr);
@@ -558,6 +557,15 @@ static inline int sock_map_prog(struct bpf_map *map,
 }
 #endif
 
+#if defined(CONFIG_EVENT_TRACING) && defined(CONFIG_BPF_SYSCALL)
+int bpf_event_query_prog_array(struct perf_event *event, void __user *info);
+#else
+static inline int bpf_event_query_prog_array(struct perf_event *event, void __user *info)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 /* verifier prototypes for helper functions called from eBPF programs */
 extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
 extern const struct bpf_func_proto bpf_map_update_elem_proto;
-- 
2.9.5

Re: [PATCH net-next] bpf/tracing: fix kernel/events/core.c compilation error

[Daniel Borkmann]

On 12/13/2017 08:42 AM, Yonghong Song wrote:
> Commit f371b304f12e ("bpf/tracing: allow user space to
> query prog array on the same tp") introduced a perf
> ioctl command to query prog array attached to the
> same perf tracepoint. The commit introduced a
> compilation error when either CONFIG_BPF_SYSCALL or
> CONFIG_EVENT_TRACING is not defined:
>   kernel/events/core.o: In function `perf_ioctl':
>   core.c:(.text+0x98c4): undefined reference to `bpf_event_query_prog_array'
> 
> This patch fixed this error.
> 
> Fixes: f371b304f12e ("bpf/tracing: allow user space to query prog array on the same tp")
> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> Signed-off-by: Yonghong Song <yhs@fb.com>

Looking at _perf_ioctl(), we also have perf_event_set_bpf_prog()
there. It's basically under CONFIG_EVENT_TRACING, which later calls
perf_event_attach_bpf_prog() which is under CONFIG_BPF_EVENTS, so
where we have the dummy handler returning -EOPNOTSUPP when BPF
events is not set. bpf_trace.c is only built when CONFIG_BPF_EVENTS
is set and that by itself depends on BPF_SYSCALL already. So it would
be more correct to do the same thing here ...

#if defined(CONFIG_EVENT_TRACING) && defined(CONFIG_BPF_EVENTS)
[...]

> ---
>  include/linux/bpf.h | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 93e15b9..8dbbfd7 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -254,7 +254,6 @@ typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,
>  
>  u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
>  		     void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy);
> -int bpf_event_query_prog_array(struct perf_event *event, void __user *info);
>  
>  int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
>  			  union bpf_attr __user *uattr);
> @@ -558,6 +557,15 @@ static inline int sock_map_prog(struct bpf_map *map,
>  }
>  #endif
>  
> +#if defined(CONFIG_EVENT_TRACING) && defined(CONFIG_BPF_SYSCALL)
> +int bpf_event_query_prog_array(struct perf_event *event, void __user *info);
> +#else
> +static inline int bpf_event_query_prog_array(struct perf_event *event, void __user *info)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#endif
> +
>  /* verifier prototypes for helper functions called from eBPF programs */
>  extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
>  extern const struct bpf_func_proto bpf_map_update_elem_proto;
> 

Re: [PATCH net-next] bpf/tracing: fix kernel/events/core.c compilation error

[Alexei Starovoitov]

On 12/13/17 7:44 AM, Daniel Borkmann wrote:
> On 12/13/2017 08:42 AM, Yonghong Song wrote:
>> Commit f371b304f12e ("bpf/tracing: allow user space to
>> query prog array on the same tp") introduced a perf
>> ioctl command to query prog array attached to the
>> same perf tracepoint. The commit introduced a
>> compilation error when either CONFIG_BPF_SYSCALL or
>> CONFIG_EVENT_TRACING is not defined:
>>   kernel/events/core.o: In function `perf_ioctl':
>>   core.c:(.text+0x98c4): undefined reference to `bpf_event_query_prog_array'
>>
>> This patch fixed this error.
>>
>> Fixes: f371b304f12e ("bpf/tracing: allow user space to query prog array on the same tp")
>> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>
> Looking at _perf_ioctl(), we also have perf_event_set_bpf_prog()
> there. It's basically under CONFIG_EVENT_TRACING, which later calls
> perf_event_attach_bpf_prog() which is under CONFIG_BPF_EVENTS, so
> where we have the dummy handler returning -EOPNOTSUPP when BPF
> events is not set. bpf_trace.c is only built when CONFIG_BPF_EVENTS
> is set and that by itself depends on BPF_SYSCALL already. So it would
> be more correct to do the same thing here ...
>
> #if defined(CONFIG_EVENT_TRACING) && defined(CONFIG_BPF_EVENTS)
> [...]

+1
#ifdef CONFIG_BPF_EVENTS
works, whereas CONFIG_EVENT_TRACING probably not, since kprobe
can be disabled independently which will turn off BPF_EVENTS
and body of bpf_event_query_prog_array() will be gone.

Re: [PATCH net-next] bpf/tracing: fix kernel/events/core.c compilation error

[Yonghong Song]

On 12/13/17 7:50 AM, Alexei Starovoitov wrote:
> On 12/13/17 7:44 AM, Daniel Borkmann wrote:
>> On 12/13/2017 08:42 AM, Yonghong Song wrote:
>>> Commit f371b304f12e ("bpf/tracing: allow user space to
>>> query prog array on the same tp") introduced a perf
>>> ioctl command to query prog array attached to the
>>> same perf tracepoint. The commit introduced a
>>> compilation error when either CONFIG_BPF_SYSCALL or
>>> CONFIG_EVENT_TRACING is not defined:
>>>   kernel/events/core.o: In function `perf_ioctl':
>>>   core.c:(.text+0x98c4): undefined reference to 
>>> `bpf_event_query_prog_array'
>>>
>>> This patch fixed this error.
>>>
>>> Fixes: f371b304f12e ("bpf/tracing: allow user space to query prog 
>>> array on the same tp")
>>> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
>>> Signed-off-by: Yonghong Song <yhs@fb.com>
>>
>> Looking at _perf_ioctl(), we also have perf_event_set_bpf_prog()
>> there. It's basically under CONFIG_EVENT_TRACING, which later calls
>> perf_event_attach_bpf_prog() which is under CONFIG_BPF_EVENTS, so
>> where we have the dummy handler returning -EOPNOTSUPP when BPF
>> events is not set. bpf_trace.c is only built when CONFIG_BPF_EVENTS
>> is set and that by itself depends on BPF_SYSCALL already. So it would
>> be more correct to do the same thing here ...
>>
>> #if defined(CONFIG_EVENT_TRACING) && defined(CONFIG_BPF_EVENTS)
>> [...]
> 
> +1
> #ifdef CONFIG_BPF_EVENTS
> works, whereas CONFIG_EVENT_TRACING probably not, since kprobe
> can be disabled independently which will turn off BPF_EVENTS
> and body of bpf_event_query_prog_array() will be gone.

I tested to enable/disable uprobe/kprobe/both and my patch works.
But I did not test  enable a non uprobe/kprobe tracing event
(e.g., CONFIG_FUNCTION_TRACER) where CONFIG_TRACING and 
CONFIG_EVENT_TRACING is on but CONFIG_UPROBES_EVENT/CONFIG_KPROBES_EVENT
is off and then my patch breaks.

Looks like
#ifdef CONFIG_BPF_EVENTS
is suffice.
This config will enable to include bpf_trace.c with the real definition. 
It will depend on KPROBE_EVENTS or UPROBE_EVENTS and either
of them will enable CONFIG_TRACING and then CONFIG_EVENT_TRACING.

Will resubmit the patch after testing.