Unable to use hardware/flash.h from pico-sdk

I hope this is the right place to open this issue.

When building something that uses functions from hardware/flash.h I get the following unresolved symbol:

.platformio/packages/toolchain-gccarmnoneeabi/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld: .pio/build/rp2040/src/main.cpp.o: in function `save()':
main.cpp:(.text._Z4savev+0x12): undefined reference to `flash_range_erase(unsigned long, unsigned int)'
.platformio/packages/toolchain-gccarmnoneeabi/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/bin/ld: main.cpp:(.text._Z4savev+0x1e): undefined reference to `flash_range_program(unsigned long, unsigned char const*, unsigned int)'
collect2: error: ld returned 1 exit status
*** [.pio/build/rp2040/firmware.elf] Error 1

This same code works fine in the Arduino IDE (1.0) and arduino-cli. The two symbols referenced are calls I'm making of course.

Is there some build_flags= that I need to set in order to link against the proper library? I have tried the released version of platform-raspberrypi as well as pointing it directly at this github repo and the behavior is the same.

Start with the reported main.cpp build for the rp2040 target and inspect the PlatformIO linker output for the unresolved flash_range_erase and flash_range_program symbols. Compare the PlatformIO setup with the working Arduino IDE and arduino-cli builds. Done means the firmware links successfully when using hardware/flash.h.