This is a very basic flashrom/serprog compatible SPI flash reader/writer for the Pico Debug'n'Dump.
It does not require a custom version of flashrom, just drag the compiled uf2 onto your Pico and you're ready to go.
export PICO_SDK_PATH=...
mkdir build
cd build
cmake
make
Dump a flashchip:
flashrom -p serprog:dev=/dev/ttyACM0:115200 -r foo.bin
The project is based on the spi_flash example by Raspberry Pi (Trading) Ltd. which is licensed under BSD-3-Clause.
As a lot of the code itself was heavily inspired/influenced by stm32-vserprog this code is licensed under GPLv3.