[PATCH 18/57] perf trace: Support tracepoint dynamic char arrays

Arnaldo Carvalho de Melo
2019-10-21T13:39:46Z

From: Arnaldo Carvalho de Melo <acme@redhat.com>

Things like:

# grep __data_loc /sys/kernel/debug/tracing/events/sched/sched_process_exec/format
field:__data_loc char[] filename; offset:8; size:4; signed:1;
#

That, at that offset (8) and with that size(8) have an integer that
contains the real length and offset for the contents of that array.

Now this works:

# perf trace --max-events 1 -e sched:*exec -a
0.000 sed/19441 sched:sched_process_exec(filename: "/usr/bin/sync", pid: 19441 (sync), old_pid: 19441 (sync))
#

As when using the libtraceevent based beautifier:

# perf trace --libtraceevent --max-events 1 -e sched:*exec -a
0.000 sync/19463 sched:sched_process_exec(filename=/usr/bin/sync pid=19463 old_pid=19463)
#

I.e. that 'filename' is implemented as a dynamic char array.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-950p0m842fe6n7sxsdwqj5i2@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/builtin-trace.c | 19 ++++++++++++++-----
tools/perf/trace/beauty/beauty.h | 2 ++
2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index cdee22dac2b3..907eaf316f5b 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -563,7 +563,7 @@ static size_t syscall_arg__scnprintf_char_array(char *bf, size_t size, struct sy
// XXX Hey, maybe for sched:sched_switch prev/next comm fields we can
// fill missing comms using thread__set_comm()...
// here or in a special syscall_arg__scnprintf_pid_sched_tp...
- return scnprintf(bf, size, "\"%-.*s\"", arg->fmt->nr_entries, arg->val);
+ return scnprintf(bf, size, "\"%-.*s\"", arg->fmt->nr_entries ?: arg->len, arg->val);
}

#define SCA_CHAR_ARRAY syscall_arg__scnprintf_char_array
@@ -1559,7 +1559,7 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
arg->scnprintf = SCA_PID;
else if (strcmp(field->type, "umode_t") == 0)
arg->scnprintf = SCA_MODE_T;
- else if ((field->flags & TEP_FIELD_IS_ARRAY) && strstarts(field->type, "char")) {
+ else if ((field->flags & TEP_FIELD_IS_ARRAY) && strstr(field->type, "char")) {
arg->scnprintf = SCA_CHAR_ARRAY;
arg->nr_entries = field->arraylen;
} else if ((strcmp(field->type, "int") == 0 ||
@@ -2523,10 +2523,19 @@ static size_t trace__fprintf_tp_fields(struct trace *trace, struct evsel *evsel,
if (syscall_arg.mask & bit)
continue;

+ syscall_arg.len = 0;
syscall_arg.fmt = arg;
- if (field->flags & TEP_FIELD_IS_ARRAY)
- val = (uintptr_t)(sample->raw_data + field->offset);
- else
+ if (field->flags & TEP_FIELD_IS_ARRAY) {
+ int offset = field->offset;
+
+ if (field->flags & TEP_FIELD_IS_DYNAMIC) {
+ offset = format_field__intval(field, sample, evsel->needs_swap);
+ syscall_arg.len = offset >> 16;
+ offset &= 0xffff;
+ }
+
+ val = (uintptr_t)(sample->raw_data + offset);
+ } else
val = format_field__intval(field, sample, evsel->needs_swap);
/*
* Some syscall args need some mask, most don't and
diff --git a/tools/perf/trace/beauty/beauty.h b/tools/perf/trace/beauty/beauty.h
index 77ad80a399fd..0dee0cf4fda8 100644
--- a/tools/perf/trace/beauty/beauty.h
+++ b/tools/perf/trace/beauty/beauty.h
@@ -87,6 +87,7 @@ struct syscall_arg_fmt;

/**
* @val: value of syscall argument being formatted
+ * @len: for tracepoint dynamic arrays, if fmt->nr_entries == 0, then its not a fixed array, look at arg->len
* @args: All the args, use syscall_args__val(arg, nth) to access one
* @augmented_args: Extra data that can be collected, for instance, with eBPF for expanding the pathname for open, etc
* @augmented_args_size: augmented_args total payload size
@@ -109,6 +110,7 @@ struct syscall_arg {
struct thread *thread;
struct trace *trace;
void *parm;
+ u16 len;
u8 idx;
u8 mask;
bool show_string_prefix;
--
2.21.0