firmware-utils: bcm4908kernel: tool adding BCM4908 kernel header

BCM4908 CFE bootloader requires kernel to be prepended with a custom
header. This simple tool implements support for such headers.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

tools/firmware-utils/Makefile

@@ -27,6 +27,7 @@ define Host/Compile
 	$(call cc,add_header)
 	$(call cc,addpattern)
 	$(call cc,asustrx)
+	$(call cc,bcm4908kernel,-Wall)
 	$(call cc,buffalo-enc buffalo-lib,-Wall)
 	$(call cc,buffalo-tag buffalo-lib,-Wall)
 	$(call cc,buffalo-tftp buffalo-lib,-Wall)

tools/firmware-utils/src/bcm4908kernel.c

@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2021 Rafał Miłecki <rafal@milecki.pl>
+ */
+
+#include <byteswap.h>
+#include <endian.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#if !defined(__BYTE_ORDER)
+#error "Unknown byte order"
+#endif
+
+#if __BYTE_ORDER == __BIG_ENDIAN
+#define cpu_to_le32(x)	bswap_32(x)
+#define le32_to_cpu(x)	bswap_32(x)
+#elif __BYTE_ORDER == __LITTLE_ENDIAN
+#define cpu_to_le32(x)	(x)
+#define le32_to_cpu(x)	(x)
+#else
+#error "Unsupported endianness"
+#endif
+
+struct bcm4908kernel_header {
+	uint32_t unk1;
+	uint32_t unk2;
+	uint32_t length;
+	uint8_t magic[4];
+	uint32_t unused;
+};
+
+static void usage() {
+	printf("Usage:\n");
+	printf("\n");
+	printf("\t-i pathname\t\t\tinput kernel filepath\n");
+	printf("\t-o pathname\t\t\toutput kernel filepath\n");
+}
+
+int main(int argc, char **argv) {
+	struct bcm4908kernel_header header;
+	uint8_t buf[1024];
+	FILE *out = NULL;
+	FILE *in = NULL;
+	size_t length;
+	size_t bytes;
+	int err = 0;
+	char c;
+
+	if (argc >= 2 && !strcmp(argv[1], "-h")) {
+		usage();
+		return 0;
+	}
+
+	while ((c = getopt(argc, argv, "i:o:")) != -1) {
+		switch (c) {
+		case 'i':
+			in = fopen(optarg, "r");
+			break;
+		case 'o':
+			out = fopen(optarg, "w+");
+			break;
+		}
+	}
+
+	if (!in || !out) {
+		fprintf(stderr, "Failed to open input and/or output file\n");
+		usage();
+		return -EINVAL;
+	}
+
+	if (fread(&header, 1, sizeof(header), in) != sizeof(header)) {
+		fprintf(stderr, "Failed to read %zu bytes from input file\n", sizeof(header));
+		err = -EIO;
+		goto err_close;
+	}
+
+	if (!memcmp(header.magic, "BRCM", 4)) {
+		fprintf(stderr, "Input file already contains BCM4908 kernel header\n");
+		err = -EIO;
+		goto err_close;
+	}
+
+	err = fseek(out, sizeof(header), SEEK_SET);
+	if (err) {
+		err = -errno;
+		fprintf(stderr, "Failed to fseek(): %d\n", err);
+		goto err_close;
+	}
+
+	length = 0;
+	rewind(in);
+	while ((bytes = fread(buf, 1, sizeof(buf), in)) > 0) {
+		if (fwrite(buf, 1, bytes, out) != bytes) {
+			fprintf(stderr, "Failed to write %zu B to the output file\n", bytes);
+			err = -EIO;
+			goto err_close;
+		}
+		length += bytes;
+	}
+
+	header.unk1 = cpu_to_le32(0x00080000);
+	header.unk2 = cpu_to_le32(0x00080000);
+	header.length = cpu_to_le32(length);
+	header.magic[0] = 'B';
+	header.magic[1] = 'R';
+	header.magic[2] = 'C';
+	header.magic[3] = 'M';
+	header.unused = 0;
+
+	fseek(out, 0, SEEK_SET);
+
+	if (fwrite(&header, 1, sizeof(header), out) != sizeof(header)) {
+		fprintf(stderr, "Failed to write header to the output file\n");
+		err = -EIO;
+		goto err_close;
+	}
+
+err_close:
+	fclose(out);
+	fclose(in);
+	return err;
+}