I'd like to start by saying that i am fully aware that windows 7 is no longer supported, and i am also aware of the implications of running an outdated vulnerable operating system on my physical machine. Moving on to my problem. I currently have a drive with grub boot loader on it with Arch linux. The drive uses GPT. I needed to dual boot with windows 7, however i am only able to boot into the windows 7 installation by enabling CMS in my motherboard. I did read that i can hack the windows 7 iso to have true uefi support by patching it with efi files, vga drivers etc but sounds like too much pain.
I booted into the installation and got till the part where it asks me to chose a partition to install, all fine and well. At this point i expected the windows installer to point out that my drive is GPT and im booted in BIOS mode and therefore the installation cannot proceed without wiping my drive, however it has not pointed that out. From the looks of it i can simply select a partition (or create one) and proceed with the installation.
However, i did not proceed because i am not sure of what the result of doing such an installation is and therefore i am not prepared in case im left with a kaput machine that will not boot without further troubleshooting. So hopefully somebody that has done this before or knows about this can tell me what i should expect after the installation, and what tools i need to have on hand to mitigate any problems in booting.
Thanks.
Edit: It seems that even though you have to enable CSM in order to get into the actual installation of Windows 7, it is still in UEFI mode and you can install as normal. Windows will add its efi files to the already existing efi partition. Then you can use your bios uefi utility to select which efi file has to be prioritized in the boot process. In my case i set it to grub and then used os-prober to add the Windows boot loader to the grub menu. Note that you will need to have CSM enabled in order to boot into Windows 7 even after installation - if you disable CSM and attempt to boot, your machine will crash. Tried this on Windows 7 N ultimate SP1 x64 bit. I'm making this edit because the question is closed and hopefully this information might be able to help someone.
