ESP32 C3 link error cmath pow function

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when building to a ESP32-C3 I get the following link error by cmath pow function…

/home/runner/work/esp32-arduino-lib-builder/esp32-arduino-lib-builder/esp-idf/components/newlib/syscalls.c:147: multiple definition of `fcntl'; c:/users/trasa/.platformio/packages/toolchain-riscv32-esp/bin/../lib/gcc/riscv32-esp-elf/8.4.0/../../../../riscv32-esp-elf/lib/rv32imc/ilp32/no-rtti\libc.a(lib_a-sysfcntl.o):/builds/idf/crosstool-NG/.build/HOST-x86_64-w64-mingw32/riscv32-esp-elf/src/newlib/newlib/libc/syscalls/sysfcntl.c:11: first defined here
c:/users/trasa/.platformio/packages/toolchain-riscv32-esp/bin/../lib/gcc/riscv32-esp-elf/8.4.0/../../../../riscv32-esp-elf/bin/ld.exe: .pio/build/airm2m_core_esp32c3/liba53/libAdafruit BME280 Library.a(Adafruit_BME280.cpp.o): in function `__gnu_cxx::__promote_2<float, double, __gnu_cxx::__promote<float, std::__is_integer<float>::__value>::__type, __gnu_cxx::__promote<double, std::__is_integer<double>::__value>::__type>::__type std::pow<float, double>(float, double)':
c:\users\trasa\.platformio\packages\toolchain-riscv32-esp\riscv32-esp-elf\include\c++\8.4.0/cmath:418: undefined reference to `pow'
collect2.exe: error: ld returned 1 exit status
*** [.pio\build\airm2m_core_esp32c3\firmware.elf] Error 1

I’m using the Adafruit BME280 library which seems to be using the math ‘pow’ function.

When building to ESP32 ‘xtensa’ with the same code everything works fine but with the ESP32-C3 ‘riscv32’ the math pow function gives undefined reference.

Anyone have an idea on why this is happening?

Using the Arduino IDE with similar code things build fine.

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You have to link it with libm.a that contains that symbol. Append your linking flags with -lm option

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I have that option in the build_flags section in the platformio.ini file but it makes no difference. Everything works fine when I use the original ESP32, it gives this problem only when I switch to the ESP32-C3. Could it be the riscv-32 toolchain?

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Sorry, I’m not familiar with platformio. But you should add this into linking flags (not cflags, compile_flags,…)

Because the order of parameters passed to command line is important here

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@fillzee , I hope this could help you Extra linker flags without -Wl, prefix — PlatformIO latest documentation

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Ok, after following suggestions and banging my head on my desk for the last 2 weeks I finally resolved the problem. After deleting all the installed platformio packages in “C:\Users\myuser.platformio\packages” and deleting the “.pio” and “.vscode” folders in the workspace folder everything finally built without issues. Platformio/VSCode downloaded and installed the packages again and things worked as should.

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