undefined reference to `main'

[CK3]

Hi,

I am currently working with the frdm K22F SDK, more precisley the dspi_half_duplex_int_master. This is a C Project and I want to integrate C++ files into it. To execute it, I decided to change the main file from .c to .cpp which leads to the following error when building it.

make -r -j8 all
Building target: frdmk22f_dspi_half_duplex_int_master.axf
Invoking: MCU Linker
arm-none-eabi-gcc -nostdlib -Xlinker -Map="frdmk22f_dspi_half_duplex_int_master.map" -Xlinker --gc-sections -Xlinker -print-memory-usage -Xlinker --sort-section=alignment -Xlinker --cref -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard -mthumb -T frdmk22f_dspi_half_duplex_int_master_Debug.ld -o "frdmk22f_dspi_half_duplex_int_master.axf" ./utilities/fsl_assert.o ./utilities/fsl_debug_console.o ./startup/startup_mk22f51212.o ./source/semihost_hardfault.o ./drivers/fsl_clock.o ./drivers/fsl_common.o ./drivers/fsl_dspi.o ./drivers/fsl_gpio.o ./drivers/fsl_lpuart.o ./drivers/fsl_smc.o ./drivers/fsl_uart.o ./device/system_MK22F51212.o ./component/uart/fsl_adapter_uart.o ./component/lists/fsl_component_generic_list.o ./board/board.o ./board/clock_config.o ./board/pin_mux.o
Memory region Used Size Region Size %age Used
PROGRAM_FLASH: 7912 B 512 KB 1.51%
c:/nxp/mcuxpressoide_11.3.0_5222/ide/plugins/com.nxp.mcuxpresso.tools.win32_11.3.0.202008311133/tools/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld.exe: c:/nxp/mcuxpressoide_11.3.0_5222/ide/plugins/com.nxp.mcuxpresso.tools.win32_11.3.0.202008311133/tools/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard\libcr_semihost_nf.a(_cr__main.o): in function `__main':
SRAM_UPPER: 8424 B 64 KB 12.85%
_cr__main.c:(.text.__main+0xa): undefined reference to `main'
collect2.exe: error: ld returned 1 exit status
SRAM_LOWER: 0 GB 64 KB 0.00%
make: *** [makefile:39: frdmk22f_dspi_half_duplex_int_master.axf] Error 1
"make -r -j8 all" terminated with exit code 2. Build might be incomplete.

From these posts: here and here it seems to me that I need to change something with the linker files. But I don't know for sure if that is the same problem.

• What causes the error?
• If it is related to the linker files, what do I need to change and how?

Thanks in advance! 

[CK3]

Hi Erich,

thanks for the quick reply. Yes it helped! I followed the steps from the link you posted and also verified for the global constructor calls. I still had some errors but they disappeared after I changed the lib from NewlibNano(none) to NewlibNano(nohost). So everything builds now fine.

However, now I don't get any output in the console now, that I got before (like "Hello World"). Do you have any idea what could cause this?

[ErichStyger · Accepted solution]

It all depends how you have 'migrated' your projects.

Keep in mind that the project nature needs to match your settings, see https://mcuoneclipse.com/2020/07/11/from-c-to-c-converting-eclipse-c-projekts/

On top of that, it all depends how you organize your calling conventions: keep in mind that main is a special symbol, plus for calling interfaces implemented in C from C++ you need to add an 'extern "C"' to manage the name mangling.

And don't forget the thing about the global constructor calls.

I hope this helps,

Erich

[CK3]

Thanks for the quick help! Do you know a solution regarding the console-output problem I now have? (see the wrongly placed reply by me)

[CK3]

Ok, I found that the problem was that I was using the nohost library variant. I swithed to semihost and now it works.