A reproduction scenario for ziglang/zig#17882, for Zig 0.11.0 and currently-latest microzig and stmicro-stm32.
Using Zig 0.11.0, zig build flash,
with st-flash installed and an STM32F3DISCOVERY board connected,
results in a debug mode .bin file which correctly
sends the text "Hello, serial port!" to the STM32F303VCT6's UART1 serial port
(460800-8-N-1).
Doing zig build flash -Drelease=true
results in a releaseSmall mode .bin file, which does not work but instead
only sends the first "H", and then the board appears to hang.
The .bin files can be recreated doing just zig build or zig build -Drelease=true,
no board or flashing needed for that.
And a copy of the .bin files is in the 'output' directory.