[Fire HD 8 and HD 10 General] r42001:
here is another try :(

C:\Windows\system32>adb shell
karnak:/ $ cd /data/local/tmp
karnak:/data/local/tmp $ chmod 755 mtk-su
karnak:/data/local/tmp $ ./mtk-su -v
param1: 0x3000, param2: 0x18020
Building symbol table
kallsyms_addresses pa 0x40baf400
kallsyms_num_syms 69054, addr_count 69054
kallsyms_names pa 0x40c36300, size 830042
kallsyms_markers pa 0x40d00e00
kallsyms_token_table pa 0x40d01700
kallsyms_token_index pa 0x40d01b00
Patching credentials
init_task va: 0xffffffc000fcea20
Possible list_head tasks at offset 0x338
0xffffffc0030c8338 0xffffffc00e76d3b8 0x000000000000008c
comm offset 0x5a8 comm: swapper/0
Found own task_struct at node 0
real_cred: 0xffffffc02919e680, cred: 0xffffffc02919e680
New UID/GID: 0/0
Parsing sel_read_enforce()
Found adrp instr at offset 4
ADRP x0, base is 0xffffffc00112e000
Found ldr instr at offset 28
LDR [x0,444], selinux_enforce VA is 0xffffffc00112e1bc
Setting selinux_enforce
Switched selinux to permissive
starting /system/bin/sh
karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # exit
1|karnak:/data/local/tmp $ mount -o remount -rw /system
mount: '/dev/block/dm-0' not user mountable in fstab
1|karnak:/data/local/tmp $ ./mtk-su -v
param1: 0x3000, param2: 0x18020
Building symbol table
kallsyms_addresses pa 0x40baf400
kallsyms_num_syms 69054, addr_count 69054
kallsyms_names pa 0x40c36300, size 830042
kallsyms_markers pa 0x40d00e00
kallsyms_token_table pa 0x40d01700
kallsyms_token_index pa 0x40d01b00
Patching credentials
init_task va: 0xffffffc000fcea20
Possible list_head tasks at offset 0x338
0xffffffc0030c8338 0xffffffc00f813138 0x000000000000008c
comm offset 0x5a8 comm: swapper/0
Found own task_struct at node 0
real_cred: 0xffffffc02e755800, cred: 0xffffffc02e755800
New UID/GID: 0/0
Parsing sel_read_enforce()
Found adrp instr at offset 4
ADRP x0, base is 0xffffffc00112e000
Found ldr instr at offset 28
LDR [x0,444], selinux_enforce VA is 0xffffffc00112e1bc
Setting selinux_enforce
Switched selinux to permissive
starting /system/bin/sh
karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # exit
1|karnak:/data/local/tmp $ chmod 755 mtk-su
karnak:/data/local/tmp $ ./mtk-su -v
param1: 0x3000, param2: 0x18020
Building symbol table
kallsyms_addresses pa 0x40baf400
kallsyms_num_syms 69054, addr_count 69054
kallsyms_names pa 0x40c36300, size 830042
kallsyms_markers pa 0x40d00e00
kallsyms_token_table pa 0x40d01700
kallsyms_token_index pa 0x40d01b00
Patching credentials
init_task va: 0xffffffc000fcea20
Possible list_head tasks at offset 0x338
0xffffffc0030c8338 0xffffffc00f813138 0x000000000000008c
comm offset 0x5a8 comm: swapper/0
Found own task_struct at node 0
real_cred: 0xffffffc0587cd700, cred: 0xffffffc0587cd700
New UID/GID: 0/0
Parsing sel_read_enforce()
Found adrp instr at offset 4
ADRP x0, base is 0xffffffc00112e000
Found ldr instr at offset 28
LDR [x0,444], selinux_enforce VA is 0xffffffc00112e1bc
Setting selinux_enforce
Switched selinux to permissive
starting /system/bin/sh
karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp # mount -o remount -rw /system
'/dev/block/dm-0' is read-only
mount: '/dev/block/dm-0'->'/system': Permission denied
1|karnak:/data/local/tmp #