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.

Signed-off-by: Howard Chu <howardchu95@gmail.com>
---
 tools/perf/builtin-trace.c      | 48 +++++++++++++++++++++++++++++++++
 tools/perf/util/trace_augment.h |  6 +++++
 2 files changed, 54 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 e7421128f589..593b0b8724d0 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)
 {
@@ -1760,6 +1765,47 @@ 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)
+{
+	char result[TRACE_AUG_MAX_BUF * 4], tens[4];
+	struct augmented_arg *augmented_arg = arg->augmented.args;
+	unsigned char *orig;
+	int i = 0, n, consumed, digits;
+
+	if (augmented_arg == NULL)
+		return 0;
+
+	orig = (unsigned char *)augmented_arg->value;
+	n = augmented_arg->size;
+
+	memset(result, 0, sizeof(result));
+
+	for (int j = 0; j < n && i < (int)sizeof(result) - 1; ++j) {
+		/* print control characters (0~31 and 127), and non-ascii characters in \(digits) */
+		if (orig[j] <= MAX_CONTROL_CHAR || orig[j] >= MAX_ASCII) {
+			result[i++] = '\\';
+
+			/* convert to digits */
+			digits = scnprintf(tens, sizeof(result) - i, "%d", (int)orig[j]);
+			if (digits + i <= (int)sizeof(result) - 1) {
+				strncpy(result + i, tens, digits);
+				i += digits;
+			}
+		} else  {
+			result[i++] = orig[j];
+		}
+	}
+
+	consumed = sizeof(*augmented_arg) + augmented_arg->size;
+	arg->augmented.args = ((void *)arg->augmented.args) + consumed;
+	arg->augmented.size -= consumed;
+
+	return scnprintf(bf, size, "\"%s\"", result);
+}
+
 static bool trace__filter_duration(struct trace *trace, double t)
 {
 	return t < (trace->duration_filter * NSEC_PER_MSEC);
@@ -1977,6 +2023,8 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
 		     strstr(field->name, "type") ||
 		     strstr(field->name, "description")))
 			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

On Thu, Aug 15, 2024 at 09:36:23AM +0800, Howard Chu wrote:
> +#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)
> +{
> +	char result[TRACE_AUG_MAX_BUF * 4], tens[4];
> +	struct augmented_arg *augmented_arg = arg->augmented.args;
> +	unsigned char *orig;
> +	int i = 0, n, consumed, digits;
> +
> +	if (augmented_arg == NULL)
> +		return 0;
> +
> +	orig = (unsigned char *)augmented_arg->value;
> +	n = augmented_arg->size;
> +
> +	memset(result, 0, sizeof(result));
> +
> +	for (int j = 0; j < n && i < (int)sizeof(result) - 1; ++j) {
> +		/* print control characters (0~31 and 127), and non-ascii characters in \(digits) */
> +		if (orig[j] <= MAX_CONTROL_CHAR || orig[j] >= MAX_ASCII) {
> +			result[i++] = '\\';
> +
> +			/* convert to digits */
> +			digits = scnprintf(tens, sizeof(result) - i, "%d", (int)orig[j]);
> +			if (digits + i <= (int)sizeof(result) - 1) {
> +				strncpy(result + i, tens, digits);
> +				i += digits;
> +			}
> +		} else  {
> +			result[i++] = orig[j];
> +		}
> +	}
> +
> +	consumed = sizeof(*augmented_arg) + augmented_arg->size;
> +	arg->augmented.args = ((void *)arg->augmented.args) + consumed;
> +	arg->augmented.size -= consumed;
> +
> +	return scnprintf(bf, size, "\"%s\"", result);
> +}

Simplified the above to the one below to avoid using multiple buffers
and copying around, now testing:

+#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;
+}