tracing: Display some syscall arrays as strings

Some of the system calls that read a fixed length of memory from the user
space address are not arrays but strings. Take a bit away from the nb_args
field in the syscall meta data to use as a flag to denote that the system
call's user_arg_size is being used as a string. The nb_args should never
be more than 6, so 7 bits is plenty to hold that number. When the
user_arg_is_str flag that, when set, will display the data array from the
user space address as a string and not an array.

This will allow the output to look like this:

  sys_sethostname(name: 0x5584310eb2a0 "debian", len: 6)

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Takaya Saeki <takayas@google.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/20251028231147.930550359@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/trace/syscall.h b/include/trace/syscall.h
index 9413c139da66..0dd7f2b33431 100644
--- a/include/trace/syscall.h
+++ b/include/trace/syscall.h
@@ -16,6 +16,7 @@
  * @name: name of the syscall
  * @syscall_nr: number of the syscall
  * @nb_args: number of parameters it takes
+ * @user_arg_is_str: set if the arg for @user_arg_size is a string
  * @user_arg_size: holds @arg that has size of the user space to read
  * @user_mask: mask of @args that will read user space
  * @types: list of types as strings
@@ -27,7 +28,8 @@
 struct syscall_metadata {
 	const char	*name;
 	int		syscall_nr;
-	u8		nb_args;
+	u8		nb_args:7;
+	u8		user_arg_is_str:1;
 	s8		user_arg_size;
 	short		user_mask;
 	const char	**types;