Re: [PATCH v3 1/6] perf: prepare perf_event.h for new types perf_kprobe and perf_uprobe

On Dec 3, 2017, at 9:03 AM, Alexei Starovoitov [off-list ref] wrote:

On Thu, Nov 30, 2017 at 03:50:18PM -0800, Song Liu wrote:

quoted

Two new perf types, perf_kprobe and perf_uprobe, will be added to allow
creating [k,u]probe with perf_event_open. These [k,u]probe are associated
with the file decriptor created by perf_event_open, thus are easy to
clean when the file descriptor is destroyed.

kprobe_func and uprobe_path are added to union config1 for pointers to
function name for kprobe or binary path for uprobe.

kprobe_addr and probe_offset are added to union config2 for kernel
address (when kprobe_func is NULL), or [k,u]probe offset.

Signed-off-by: Song Liu <redacted>
Reviewed-by: Yonghong Song <redacted>
Reviewed-by: Josef Bacik <redacted>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
include/uapi/linux/perf_event.h | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 362493a..247c6cb 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h

@@ -299,6 +299,8 @@ enum perf_event_read_format {

#define PERF_ATTR_SIZE_VER4	104	/* add: sample_regs_intr */
#define PERF_ATTR_SIZE_VER5	112	/* add: aux_watermark */

+#define MAX_PROBE_FUNC_NAME_LEN 64

I think we have to remove this restriction.
There are already functions with names longer than 64 characters
in the current vmlinux:
trace_event_define_fields_ext4_ext_convert_to_initialized_fastpath
trace_event_define_fields_mm_vmscan_direct_reclaim_begin_template

How about we drop this restriction and use NAME_MAX internally
without adding new uapi defines ?

Yeah, I agree that we should drop this uapi define. How about we use

#define KSYM_NAME_LEN 128

If a function name is longer than KSYM_NAME_LEN, we get warning like:

Symbol long_long_name_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_ too long for kallsyms (204 vs 128).
Please increase KSYM_NAME_LEN both in kernel and kallsyms.c

Thanks,
Song