Please, can you explain how to use it ?
Examples ? Anything ? Has anyone used it with success ?

I myself could unpack, but ' mkbootimg ' never worked once.

It simply always says the same - no error, just repeats " usage: mkbootimg ... " ; I don't get what's wrong, there's nothing wrong but still only that message no matter what options I put or don't put.

I'll give you examples:

my command > ~/Bin/android-unpackbootimg/mkbootimg --kernel boot/boot.img-zImage --ramdisk boot/boot.img-ramdisk.gz --cmdline "console=null androidboot.hardware=qcom msm_rtb.filter=0x237 ehci-hcd.park=3 androidboot.bootdevice=7824900.sdhci lpm_levels.sleep_disabled=1 androidboot.selinux=permissive" --base 0x80000000 --pagesize 2048 --kernel_offset 0x00008000 --ramdisk_offset 0x02000000 second_offset 0x00f00000 --tags_offset 01e00000 --os_version 8.1.0 --os_patch_level 2019-04 --hash sha1 -o boot2.img

output > usage: mkbootimg
--kernel
[ --ramdisk ]
[ --second <2ndbootloader-filename> ]
[ --cmdline ]
[ --board ]
[ --base

I tried all combinations I could think, yet nothing. Well, if I only use one param it does output an image that never matches the original ; I suppose because it lacks the info from those parameters.

On the other hand, the python implementation does accept all params but the output never matches the input by little, but sill not the same.
Not to mention the simple adjusts I had to make. For instance, now hex numbers must be precceded by ' 0x '. Some params are filenames other are the files content and so on.

My best regards

log:
~/dtimgextract/unpack$ ../dtimgextract ../boot.img-dtb
qc_magic: QCDT
version: 3
count: 204
header v3 format not implemented

When I try to unapck an android 4.4 boot.img-dtb file, it does not work.

$ make
make: ar: No such file or directory.
make: *** [Makefile:45: mincrypt] Error 127

Looks like the source assumes the input is a normal file and not a block special device.

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7a9ccbb in __mempcpy_sse2 () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff7a9ccbb in __mempcpy_sse2 () from /lib64/libc.so.6
#1  0x00007ffff7a877ee in __GI__IO_file_xsgetn () from /lib64/libc.so.6
#2  0x00007ffff7a7c1ef in fread () from /lib64/libc.so.6
#3  0x0000000000402253 in main (argc=0, argv=0x7fffffffe400) at unpackbootimg.c:293
(gdb) up 3
#3  0x0000000000402253 in main (argc=0, argv=0x7fffffffe400) at unpackbootimg.c:293
293                 if(fread(second_test, second_test_size, 1, f)){};
(gdb) list
288             struct stat st;
289             stat(filename, &st);
290             int second_test_size = st.st_size - total_read;
291             if (second_test_size > header.dt_size) {
292                 byte* second_test = (byte*)malloc(second_test_size);
293                 if(fread(second_test, second_test_size, 1, f)){};
294                 u_int16_t *sbuf = (u_int16_t*)second_test;
295                 if (sbuf[0]) {
296                     int second_size = 0;
297                     while (sbuf[0]) {
(gdb) p second_test_size
$1 = -8976384
(gdb) p st.st_size
$2 = 0
(gdb) p filename
$3 = 0x7fffffffe6ad "/dev/loop10p30"