VisualGDB uses the GNU Linker to link the built executables. You can pass additional flags to the linker via project properties (exact location depends on the project type). That said, we are not aware of any linker setting that would pad the ELF file up to the size of the MCU FLASH. You might be able to get it working with some tweaks to the linker script, but it’s not something that VisualGDB can do out-of-the-box.