tracing: Show printable characters in syscall arrays

When displaying the contents of the user space data passed to the kernel,
instead of just showing the array values, also print any printable
content.

Instead of just:

  bash-1113    [003] .....  3433.290654: sys_write(fd: 2, buf: 0x555a8deeddb0 (72:6f:6f:74:40:64:65:62:69:61:6e:2d:78:38:36:2d:36:34:3a:7e:23:20), count: 0x16)

Display:

  bash-1113    [003] .....  3433.290654: sys_write(fd: 2, buf: 0x555a8deeddb0 (72:6f:6f:74:40:64:65:62:69:61:6e:2d:78:38:36:2d:36:34:3a:7e:23:20) "root@debian-x86-64:~# ", count: 0x16)

This only affects tracing and does not affect perf, as this only updates
the output from the kernel. The output from perf is via user space. This
may change by an update to libtraceevent that will then update perf to
have this as well.

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/20251028231148.429422865@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index a2de6364777a9e28f279e207dd2b6821c4e6a145..2d1307f13e133592ed5c015510ddaf19cc77439c 100644 (file)
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -155,6 +155,8 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
        trace_seq_printf(s, "%s(", entry->name);
 
        for (i = 0; i < entry->nb_args; i++) {
+               bool printable = false;
+               char *str;
 
                if (trace_seq_has_overflowed(s))
                        goto end;
@@ -193,8 +195,11 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
 
                val = trace->args[entry->user_arg_size];
 
+               str = ptr;
                trace_seq_puts(s, " (");
                for (int x = 0; x < len; x++, ptr++) {
+                       if (isascii(*ptr) && isprint(*ptr))
+                               printable = true;
                        if (x)
                                trace_seq_putc(s, ':');
                        trace_seq_printf(s, "%02x", *ptr);
@@ -203,6 +208,22 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
                        trace_seq_printf(s, ", %s", EXTRA);
 
                trace_seq_putc(s, ')');
+
+               /* If nothing is printable, don't bother printing anything */
+               if (!printable)
+                       continue;
+
+               trace_seq_puts(s, " \"");
+               for (int x = 0; x < len; x++) {
+                       if (isascii(str[x]) && isprint(str[x]))
+                               trace_seq_putc(s, str[x]);
+                       else
+                               trace_seq_putc(s, '.');
+               }
+               if (len < val)
+                       trace_seq_printf(s, "\"%s", EXTRA);
+               else
+                       trace_seq_putc(s, '"');
        }
 
        trace_seq_putc(s, ')');