fastboot: [boot] and [flash:raw] command support boot v4

Boot v4 is mostly compatible with boot v3, so these minimal changes
should be sufficient.
The newly introduced field of v4, signature_size, is left zero because
this field is only meant to be read by VTS testcases, so the value
doesn't matter for the debugging purposes of boot and flash:raw.

Bug: 183455415
Test: Manual
Change-Id: I5c2737ce35dd25f318b19a429de805ea16c46607
diff --git a/fastboot/bootimg_utils.cpp b/fastboot/bootimg_utils.cpp
index 2c0989e..6ba751a 100644
--- a/fastboot/bootimg_utils.cpp
+++ b/fastboot/bootimg_utils.cpp
@@ -34,22 +34,22 @@
 #include <stdlib.h>
 #include <string.h>
 
-static void bootimg_set_cmdline_v3(boot_img_hdr_v3* h, const std::string& cmdline) {
+static void bootimg_set_cmdline_v3_and_above(boot_img_hdr_v3* h, const std::string& cmdline) {
     if (cmdline.size() >= sizeof(h->cmdline)) die("command line too large: %zu", cmdline.size());
     strcpy(reinterpret_cast<char*>(h->cmdline), cmdline.c_str());
 }
 
 void bootimg_set_cmdline(boot_img_hdr_v2* h, const std::string& cmdline) {
-    if (h->header_version == 3) {
-        return bootimg_set_cmdline_v3(reinterpret_cast<boot_img_hdr_v3*>(h), cmdline);
+    if (h->header_version >= 3) {
+        return bootimg_set_cmdline_v3_and_above(reinterpret_cast<boot_img_hdr_v3*>(h), cmdline);
     }
     if (cmdline.size() >= sizeof(h->cmdline)) die("command line too large: %zu", cmdline.size());
     strcpy(reinterpret_cast<char*>(h->cmdline), cmdline.c_str());
 }
 
-static boot_img_hdr_v3* mkbootimg_v3(const std::vector<char>& kernel,
-                                     const std::vector<char>& ramdisk, const boot_img_hdr_v2& src,
-                                     std::vector<char>* out) {
+static boot_img_hdr_v3* mkbootimg_v3_and_above(const std::vector<char>& kernel,
+                                               const std::vector<char>& ramdisk,
+                                               const boot_img_hdr_v2& src, std::vector<char>* out) {
 #define V3_PAGE_SIZE 4096
     const size_t page_mask = V3_PAGE_SIZE - 1;
     int64_t kernel_actual = (kernel.size() + page_mask) & (~page_mask);
@@ -65,7 +65,12 @@
     hdr->ramdisk_size = ramdisk.size();
     hdr->os_version = src.os_version;
     hdr->header_size = sizeof(boot_img_hdr_v3);
-    hdr->header_version = 3;
+    hdr->header_version = src.header_version;
+
+    if (src.header_version >= 4) {
+        auto hdr_v4 = reinterpret_cast<boot_img_hdr_v4*>(hdr);
+        hdr_v4->signature_size = 0;
+    }
 
     memcpy(hdr->magic + V3_PAGE_SIZE, kernel.data(), kernel.size());
     memcpy(hdr->magic + V3_PAGE_SIZE + kernel_actual, ramdisk.data(), ramdisk.size());
@@ -76,11 +81,13 @@
 boot_img_hdr_v2* mkbootimg(const std::vector<char>& kernel, const std::vector<char>& ramdisk,
                            const std::vector<char>& second, const std::vector<char>& dtb,
                            size_t base, const boot_img_hdr_v2& src, std::vector<char>* out) {
-    if (src.header_version == 3) {
+    if (src.header_version >= 3) {
         if (!second.empty() || !dtb.empty()) {
-            die("Second stage bootloader and dtb not supported in v3 boot image\n");
+            die("Second stage bootloader and dtb not supported in v%d boot image\n",
+                src.header_version);
         }
-        return reinterpret_cast<boot_img_hdr_v2*>(mkbootimg_v3(kernel, ramdisk, src, out));
+        return reinterpret_cast<boot_img_hdr_v2*>(
+                mkbootimg_v3_and_above(kernel, ramdisk, src, out));
     }
     const size_t page_mask = src.page_size - 1;