BusyBox v1.10.2 (Debian 3:1.10.2.legal-1osso30+0m5) built-in shell (ash)
Enter 'help' for a list of built-in commands.

~ $ sudo gainroot
Root shell enabled


BusyBox v1.10.2 (Debian 3:1.10.2.legal-1osso30+0m5) built-in shell (ash)
Enter 'help' for a list of built-in commands.

/home/user # echo "unit: sectors
>  /dev/mmcblk0p1 : start= 16, size= 7554080, Id=c" > table
/home/user # sfdisk  --no-reread /dev/mmcblk1 < table

Disk /dev/mmcblk1: 0 cylinders, 4 heads, 16 sectors/track
read: Inappropriate ioctl for device

sfdisk: read error on /dev/mmcblk1 - cannot read sector 0
 /dev/mmcblk1: unrecognized partition table type
Old situation:
No partitions found
Warning: given size (7554080) exceeds max allowable size (0)

sfdisk: bad input
/home/user #