tracing/user_events: Fix non-spaced field matching

When the ABI was updated to prevent same name w/different args, it missed an important corner case when fields don't end with a space. Typically, space is used for fields to help separate them, like "u8 field1; u8 field2". If no spaces are used, like
"u8 field1;u8 field2", then the parsing works for the first time. However, the match check fails on a subsequent register, leading to confusion.

This is because the match check uses argv_split() and assumes that all fields will be split upon the space. When spaces are used, we get back { "u8", "field1;" }, without spaces we get back { "u8", "field1;u8" }. This causes a mismatch, and the user program gets back -EADDRINUSE.

Add a method to detect this case before calling argv_split(). If found force a space after the field separator character ';'. This ensures all cases work properly for matching.

I could not find an existing function to accomplish this, so I had to hand code a copy with this logic. If there is a better way to achieve this, I'm all ears.

This series also adds a selftest to ensure this doesn't break again.

With this fix, the following are all treated as matching:
u8 field1;u8 field2
u8 field1; u8 field2
u8 field1;\tu8 field2
u8 field1;\nu8 field2

V2 changes:
Renamed fix_semis_no_space() to insert_space_after_semis(). Have user_event_argv_split() return fast in no-split case. Pulled in Masami's shorter loop in insert_space_after_semis().

Beau Belgrave (2):
tracing/user_events: Fix non-spaced field matching selftests/user_events: Add non-spacing separator check

 kernel/trace/trace_events_user.c              | 76 ++++++++++++++++++-
 .../selftests/user_events/ftrace_test.c       |  8 ++
 2 files changed, 83 insertions(+), 1 deletion(-)

base-commit: 0bbac3facb5d6cc0171c45c9873a2dc96bea9680

2.34.1