[PATCH v4 09/13] tracing: Show printable characters in syscall arrays

Steven Rostedt
2025-10-21T00:52:13Z

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.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace_syscalls.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 8faba968c9c0..b589bdc28f59 100644
--- 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, ')');
--
2.51.0