tools: mtrace-reader.c: add C version of mtrace-reader.py

Add a C implementation of mtrace-reader.py for use in environments
where Python is not available.

No Cmake rules added as the mtrace-reader.py remains the preferred
tool to use.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

Author: kv2019i

tools/mtrace/mtrace-reader.c

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: BSD-3-Clause
+//
+// Copyright(c) 2025 Intel Corporation.
+//
+// Author: Kai Vehmanen <kai.vehmanen@linux.intel.com>
+//
+// Compile instructions:
+//   gcc -o mtrace-reader mtrace-reader.c -Wall -O2
+//
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <stdint.h>
+
+#define READ_BUFFER 16384
+#define MTRACE_FILE "/sys/kernel/debug/sof/mtrace/core0"
+
+uint8_t buffer[READ_BUFFER];
+
+int main(void)
+{
+	ssize_t read_bytes;
+	uint32_t data_len;
+	uint32_t header;
+	int fd;
+
+	fd = open(MTRACE_FILE, O_RDONLY);
+	if (fd < 0) {
+		perror("open");
+		return 1;
+	}
+
+	while (1) {
+		read_bytes = read(fd, buffer, READ_BUFFER);
+
+		/* handle end-of-file */
+		if (read_bytes == 0)
+			continue;
+
+		if (read_bytes <= 4)
+			continue;
+
+		header = *(uint32_t *)buffer;
+		data_len = header;
+		if (data_len > read_bytes - 4)
+			continue;
+
+		if (write(STDOUT_FILENO, buffer + 4, data_len) < 0) {
+			perror("write");
+			return -1;
+		}
+	}
+
+	close(fd);
+
+	return 0;
+}