[PATCH v3 5/8] perf trace: Pretty print buffer data

[Howard Chu]

Define TRACE_AUG_MAX_BUF in trace_augment.h data, which is the maximum
buffer size we can augment. BPF will include this header too.

Print buffer in a way that's different than just printing a string, we
print all the control characters in \digits (such as \0 for null, and
\10 for newline, LF).

For character that has a bigger value than 127, we print the digits
instead of the character itself as well.

Committer notes:

Simplified the buffer scnprintf to avoid using multiple buffers as
discussed in the patch review thread.

Signed-off-by: Howard Chu <howardchu95@xxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240815013626.935097-8-howardchu95@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/builtin-trace.c      | 33 +++++++++++++++++++++++++++++++++
 tools/perf/util/trace_augment.h |  6 ++++++
 2 files changed, 39 insertions(+)
 create mode 100644 tools/perf/util/trace_augment.h

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 048bcb92624c..470d74e3f875 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -65,6 +65,7 @@
 #include "syscalltbl.h"
 #include "rb_resort.h"
 #include "../perf.h"
+#include "trace_augment.h"
 
 #include <errno.h>
 #include <inttypes.h>
@@ -852,6 +853,10 @@ static size_t syscall_arg__scnprintf_filename(char *bf, size_t size,
 
 #define SCA_FILENAME syscall_arg__scnprintf_filename
 
+static size_t syscall_arg__scnprintf_buf(char *bf, size_t size, struct syscall_arg *arg);
+
+#define SCA_BUF syscall_arg__scnprintf_buf
+
 static size_t syscall_arg__scnprintf_pipe_flags(char *bf, size_t size,
 						struct syscall_arg *arg)
 {
@@ -1745,6 +1750,32 @@ static size_t syscall_arg__scnprintf_filename(char *bf, size_t size,
 	return 0;
 }
 
+#define MAX_CONTROL_CHAR 31
+#define MAX_ASCII 127
+
+static size_t syscall_arg__scnprintf_buf(char *bf, size_t size, struct syscall_arg *arg)
+{
+	struct augmented_arg *augmented_arg = arg->augmented.args;
+	unsigned char *orig = (unsigned char *)augmented_arg->value;
+	size_t printed = 0;
+	int consumed;
+
+	if (augmented_arg == NULL)
+		return 0;
+
+	for (int j = 0; j < augmented_arg->size; ++j) {
+		bool control_char = orig[j] <= MAX_CONTROL_CHAR || orig[j] >= MAX_ASCII;
+		/* print control characters (0~31 and 127), and non-ascii characters in \(digits) */
+		printed += scnprintf(bf + printed, size - printed, control_char ? "\\%d" : "%c", (int)orig[j]);
+	}
+
+	consumed = sizeof(*augmented_arg) + augmented_arg->size;
+	arg->augmented.args = ((void *)arg->augmented.args) + consumed;
+	arg->augmented.size -= consumed;
+
+	return printed;
+}
+
 static bool trace__filter_duration(struct trace *trace, double t)
 {
 	return t < (trace->duration_filter * NSEC_PER_MSEC);
@@ -1956,6 +1987,8 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
 		    ((len >= 4 && strcmp(field->name + len - 4, "name") == 0) ||
 		     strstr(field->name, "path") != NULL))
 			arg->scnprintf = SCA_FILENAME;
+		else if (strstr(field->type, "char *") && strstr(field->name, "buf"))
+			arg->scnprintf = SCA_BUF;
 		else if ((field->flags & TEP_FIELD_IS_POINTER) || strstr(field->name, "addr"))
 			arg->scnprintf = SCA_PTR;
 		else if (strcmp(field->type, "pid_t") == 0)
diff --git a/tools/perf/util/trace_augment.h b/tools/perf/util/trace_augment.h
new file mode 100644
index 000000000000..57a3e5045937
--- /dev/null
+++ b/tools/perf/util/trace_augment.h
@@ -0,0 +1,6 @@
+#ifndef TRACE_AUGMENT_H
+#define TRACE_AUGMENT_H
+
+#define TRACE_AUG_MAX_BUF 32 /* for buffer augmentation in perf trace */
+
+#endif
-- 
2.45.2