The *.xml stack file creation is different if you are going for Solution Manager 7.2 SPS 9 Upgrade from Solution Manager 7.1.
As of SAP Solution Manager 7.2 SPS 9, the ABAP stack and the Java stack are on different SAP NetWeaver releases. The ABAP stack is based on SAP NetWeaver 7.4 and the Java stack is based on SAP NetWeaver 7.5.
Procedure:
1- Follow the instructions of SAP Note 2287046 and generate the system info *.xml file of the ABAP and Java stacks of your existing SAP Solution Manager 7.1 installation.
2- Post generation of *.xml file from ABAP and JAVA, Add the system at SAP Maintenance Planner, choose Explore Systems and upload the system information *.xml files one by one for the ABAP and the Java stack.

3- In the list, select the ABAP stack of SAP Solution Manager. The maintenance plan cycle of your system is displayed.
4- Choose the system name in the centre of the maintenance plan cycle.

5- Choose Dependencies in the menu on the left.

6- Choose + to add dependencies and Add the Java stack and select Minimum impact. Choose OK.

7- Save your entries and return to the maintenance plan cycle.
8- In the upper right corner, select the Personalize option in the menu under your user name. In the Personlize dialog box, choose Verify Systems and then select the Enable Edit System checkbox.

You are now on a screen guiding you through the verification steps.
9- In the Edit System step, check that the following is shown:

10- Choose Next. In the following steps, Verify Products and Verify Dependencies, also choose Next.
11- Complete the process and save. Then return to the maintenance plan cycle.
12- In the cycle, choose Plan.
13- You are now on a screen guiding you through the planning steps.
14- In the Define Change step, select the Plan a Maintenance option.
15- For SAP Solution Manager 7.2, select both the Solution Manager ABAP Stack and the Solution Manager JAVA Stack checkboxes:

16- Choose Next.
17- In the Select Files step, choose the Kernel files and choose Confirm Selection.
18- Choose Next.
19- In the Download Files step, choose Download Stack XML. Then choose Push to Download Basket to push the delta archives to the download basket.
Now the files are ready for the upgrade of your SAP Solution Manager 7.1 to SAP Solution Manager 7.2 SPS 9.
I hope you will find this blog useful to create the *.xml file for Solution Manager 7.2 SPS 9 upgrade.
Thank you!!
References:
1- Upgrade Guide - SAP Solution Manager 7.2
2- 2287046 - How to Generate the System Info XML and upload to Maintenance Planner