[PATCH] perf trace: Add --bitmask-list option and correct cpumask formatting
From: Aaron Tomlin
Date: Tue Jul 14 2026 - 12:31:54 EST
Currently, dynamic non-array fields such as 'cpumask_t' are mishandled
in 'perf trace', causing the raw length and offset descriptors to be
interpreted and displayed as a literal integer (e.g., 'cpumask: 524320'
instead of the actual mask data).
This patch corrects the parsing of dynamic fields that do not have the
TEP_FIELD_IS_ARRAY flag set. By doing so, it ensures the pointer to the
raw bits is properly resolved within the payload.
Furthermore, it improves the display formatting for 'cpumask' types:
- By default, the cpumask is now correctly output as a zero-suppressed
hexadecimal string, resolving the aforementioned integer display
anomaly
- A new '--bitmask-list' command-line option has been introduced.
When specified, this delegates formatting to 'bitmap_scnprintf()',
enabling the cpumask to be rendered as a condensed, human-readable
list (e.g., '0,2-5,7')
Fixes: c5e006cdbd27 ("perf trace: Support tracepoint dynamic char arrays")
Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxxx>
---
tools/perf/builtin-trace.c | 70 ++++++++++++++++++++++++++++++++------
tools/perf/util/evsel.c | 29 ++++++++++++++++
tools/perf/util/evsel.h | 3 ++
3 files changed, 92 insertions(+), 10 deletions(-)
diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index ba0f8749fc7d..cd75ac4e5169 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -226,6 +226,7 @@ struct trace {
bool force;
bool vfs_getname;
bool force_btf;
+ bool bitmask_list;
bool summary_bpf;
int trace_pgfaults;
char *perfconfig_events;
@@ -3216,7 +3217,7 @@ static size_t trace__fprintf_tp_fields(struct trace *trace, struct perf_sample *
const struct tep_event *tp_format = evsel__tp_format(evsel);
struct tep_format_field *field = tp_format ? tp_format->format.fields : NULL;
struct syscall_arg_fmt *arg = __evsel__syscall_arg_fmt(evsel);
- size_t printed = 0, btf_printed;
+ size_t printed = 0, btf_printed, saved_printed;
unsigned long val;
u8 bit = 1;
struct syscall_arg syscall_arg = {
@@ -3238,17 +3239,65 @@ static size_t trace__fprintf_tp_fields(struct trace *trace, struct perf_sample *
syscall_arg.len = 0;
syscall_arg.fmt = arg;
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;
- if (tep_field_is_relative(field->flags))
- offset += field->offset + field->size;
+ void *ptr = format_field__get_raw_data(field, sample,
+ evsel->needs_swap,
+ &syscall_arg.len);
+
+ if (!ptr) {
+ pr_err("Problem processing %s field, skipping...\n", field->name);
+ continue;
+ }
+ val = (uintptr_t)ptr;
+ } else if ((field->flags & TEP_FIELD_IS_DYNAMIC) &&
+ strstr(field->type, "cpumask")) {
+ void *ptr = format_field__get_raw_data(field, sample,
+ evsel->needs_swap,
+ &syscall_arg.len);
+
+ if (!ptr) {
+ pr_err("Problem processing %s field, skipping...\n", field->name);
+ continue;
}
+ val = (uintptr_t)ptr;
- val = (uintptr_t)(sample->raw_data + offset);
+ saved_printed = printed;
+
+ printed += scnprintf(bf + printed, size - printed, "%s", printed ? ", " : "");
+ if (trace->show_arg_names)
+ printed += scnprintf(bf + printed, size - printed, "%s: ", field->name);
+
+ if (trace->bitmask_list) {
+ if (syscall_arg.len > 0) {
+ unsigned long *mask = zalloc(BITS_TO_LONGS(syscall_arg.len * 8) * sizeof(unsigned long));
+ if (!mask) {
+ pr_err("Problem processing %s field, skipping...\n", field->name);
+ printed = saved_printed;
+ continue;
+ }
+ memcpy(mask, (void *)val, syscall_arg.len);
+ printed += bitmap_scnprintf(mask, syscall_arg.len * 8,
+ bf + printed, size - printed);
+ free(mask);
+ }
+ } else {
+ unsigned char *b = (unsigned char *)val;
+ int i;
+ bool skip_zero = true;
+
+ printed += scnprintf(bf + printed, size - printed, "0x");
+ /* Print in little-endian order */
+ for (i = syscall_arg.len - 1; i >= 0; i--) {
+ if (skip_zero && b[i] == 0 && i > 0)
+ continue;
+ if (skip_zero) {
+ printed += scnprintf(bf + printed, size - printed, "%x", b[i]);
+ skip_zero = false;
+ } else {
+ printed += scnprintf(bf + printed, size - printed, "%02x", b[i]);
+ }
+ }
+ }
+ continue;
} else
val = format_field__intval(field, sample, evsel->needs_swap);
/*
@@ -5537,6 +5586,7 @@ int cmd_trace(int argc, const char **argv)
"start"),
OPT_BOOLEAN(0, "force-btf", &trace.force_btf, "Prefer btf_dump general pretty printer"
"to customized ones"),
+ OPT_BOOLEAN(0, "bitmask-list", &trace.bitmask_list, "Show bitmask as a human-readable list"),
OPT_BOOLEAN(0, "bpf-summary", &trace.summary_bpf, "Summary syscall stats in BPF"),
OPT_INTEGER(0, "max-summary", &trace.max_summary,
"Max number of entries in the summary."),
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index ea9fa04429f0..0d5eb2cc4ce5 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -3933,6 +3933,35 @@ void *perf_sample__rawptr(struct perf_sample *sample, const char *name)
return sample->raw_data + offset;
}
+void *format_field__get_raw_data(struct tep_format_field *field, struct
+ perf_sample *sample, bool needs_swap,
+ u16 *len_out)
+{
+ int offset = field->offset;
+ int size = field->size;
+
+ if (field->flags & TEP_FIELD_IS_DYNAMIC) {
+ unsigned int dynamic_data;
+
+ if (out_of_bounds(field, field->offset, 4, sample->raw_size))
+ return NULL;
+
+ dynamic_data = format_field__intval(field, sample, needs_swap);
+
+ offset = dynamic_data & 0xffff;
+ size = (dynamic_data >> 16) & 0xffff;
+
+ if (tep_field_is_relative(field->flags))
+ offset += field->offset + field->size;
+ }
+
+ if (out_of_bounds(field, offset, size, sample->raw_size))
+ return NULL;
+
+ *len_out = size;
+ return sample->raw_data + offset;
+}
+
u64 format_field__intval(struct tep_format_field *field, struct perf_sample *sample,
bool needs_swap)
{
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 163fc2b6a7ea..1babfecc5d13 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -400,6 +400,9 @@ static inline char *perf_sample__strval(struct perf_sample *sample, const char *
struct tep_format_field;
+void *format_field__get_raw_data(struct tep_format_field *field,
+ struct perf_sample *sample,
+ bool needs_swap, u16 *len_out);
u64 format_field__intval(struct tep_format_field *field, struct perf_sample *sample, bool needs_swap);
#ifdef HAVE_LIBTRACEEVENT
--
2.54.0