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>

diff --git a/include/trace/syscall.h b/include/trace/syscall.h
index 9413c139da6657175ca3522bf418910720158d2b..0dd7f2b33431d206a04429ea968d3b04047c8ea4 100644 (file)
--- 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;

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 3f3cdfc9958e6e78697dd640d2065c648ff04ae4..b8e9774a8abd0fe5f8da05a64cec0d4dedec316b 100644 (file)
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -184,7 +184,7 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
                ptr = (void *)ent + (val & 0xffff);
                len = val >> 16;
 
-               if (entry->user_arg_size < 0) {
+               if (entry->user_arg_size < 0 || entry->user_arg_is_str) {
                        trace_seq_printf(s, " \"%.*s\"", len, ptr);
                        continue;
                }
@@ -249,6 +249,7 @@ print_syscall_exit(struct trace_iterator *iter, int flags,
 static int __init
 __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
 {
+       bool is_string = entry->user_arg_is_str;
        int i;
        int pos = 0;
 
@@ -266,7 +267,7 @@ __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
                        continue;
 
                /* Add the format for the user space string or array */
-               if (entry->user_arg_size < 0)
+               if (entry->user_arg_size < 0 || is_string)
                        pos += snprintf(buf + pos, LEN_OR_ZERO, " \\\"%%s\\\"");
                else
                        pos += snprintf(buf + pos, LEN_OR_ZERO, " (%%s)");
@@ -279,7 +280,7 @@ __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
                if (!(BIT(i) & entry->user_mask))
                        continue;
                /* The user space data for arg has name __<arg>_val */
-               if (entry->user_arg_size < 0) {
+               if (entry->user_arg_size < 0 || is_string) {
                        pos += snprintf(buf + pos, LEN_OR_ZERO, ", __get_str(__%s_val)",
                                        entry->args[i]);
                } else {
@@ -781,6 +782,21 @@ static void check_faultable_syscall(struct trace_event_call *call, int nr)
                sys_data->user_mask = BIT(1);
                sys_data->user_arg_size = 2;
                break;
+       /* user arg 0 with size arg at 1 as string */
+       case __NR_setdomainname:
+       case __NR_sethostname:
+               sys_data->user_mask = BIT(0);
+               sys_data->user_arg_size = 1;
+               sys_data->user_arg_is_str = 1;
+               break;
+#ifdef __NR_kexec_file_load
+       /* user arg 4 with size arg at 3 as string */
+       case __NR_kexec_file_load:
+               sys_data->user_mask = BIT(4);
+               sys_data->user_arg_size = 3;
+               sys_data->user_arg_is_str = 1;
+               break;
+#endif
        /* user arg at position 0 */
 #ifdef __NR_access
        case __NR_access: