* Linker won't bail out on non-existing functions?
@ 2020-09-04 10:18 Josef Wolf
2020-09-04 11:45 ` Alexander Monakov
0 siblings, 1 reply; 3+ messages in thread
From: Josef Wolf @ 2020-09-04 10:18 UTC (permalink / raw)
To: gcc-help
Hello,
I have an effect here which is somewhat surprising to me. The linker won't
complain on non-defined functions. There's only a warning at compile-time
about missing prototype. When I try to set a breakpoint in gdb, gdb
complains that the function is not defined:
(gdb) break delay_ms
Function "delay_ms" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb)
But this is on an embedded system, statically built. There's even an
explicit "-Wl,-Bstatic" and ldd confirms that this is not a shared
library (please see below)
BTW: There's nothing special about this function name. I tried really wired
function names with the same effect. So it's not that this function might
be defined internally somehow.
So why won't the linker bail out when it can't resolve a reference?
Any hints?
/usr/local/crossgcc/arm-none-eabi/bin/arm-none-eabi-gcc -c -mcpu=cortex-m4 -mthumb -mfpu=fpv4-sp-d16 -mfloat-abi=hard -DUSE_HAL_DRIVER -DSTM32F429xx -Icubemx/Core/Inc -Icubemx/Drivers/STM32F4xx_HAL_Driver/Inc -Icubemx/Drivers/STM32F4xx_HAL_Driver/Inc/Legacy -Icubemx/Drivers/CMSIS/Device/ST/STM32F4xx/Include -Icubemx/Drivers/CMSIS/Include -Icubemx/Middlewares/Third_Party/FreeRTOS/Source/include -Icubemx/Middlewares/Third_Party/FreeRTOS/Source/CMSIS_RTOS_V2 -Icubemx/Middlewares/Third_Party/FreeRTOS/Source/portable/GCC/ARM_CM4F -O3 -std=c99 -pedantic -Wall -fdata-sections -ffunction-sections -g -gdwarf-2 -MMD -MP -MF"app/blinkenlight.d" -Wa,-a,-ad,-alms=build/blinkenlight.lst app/blinkenlight.c -o app/blinkenlight.o
app/blinkenlight.c: In function 'blinkenlight':
app/blinkenlight.c:41:9: warning: implicit declaration of function 'delay_ms' [-Wimplicit-function-declaration]
41 | delay_ms (uval&1 ? ld->ms_on : ld->ms_off);
| ^~~~~~~~
/usr/local/crossgcc/arm-none-eabi/bin/arm-none-eabi-gcc cubemx/Core/Src/main.o cubemx/Core/Src/stm32f4xx_it.o cubemx/Core/Src/stm32f4xx_hal_msp.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_tim.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_tim_ex.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_rcc.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_rcc_ex.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_flash.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_flash_ex.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_flash_ramfunc.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_gpio.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_dma_ex.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_dma.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_pwr.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_pwr_ex.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_cortex.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_exti.o cubemx/Core/Src/system_stm32f4xx.o cubemx/Core/Src/gpio.o cubemx/Core/Src/usart.o cubemx/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_uart.o cubemx/Core/Src/freertos.o cubemx/Core/Src/stm32f4xx_hal_timebase_tim.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/croutine.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/event_groups.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/list.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/queue.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/stream_buffer.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/tasks.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/timers.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/CMSIS_RTOS_V2/cmsis_os2.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/portable/MemMang/heap_4.o cubemx/Middlewares/Third_Party/FreeRTOS/Source/portable/GCC/ARM_CM4F/port.o app/blinkenlight.o cubemx/startup_stm32f429xx.s -mcpu=cortex-m4 -mthumb -mfpu=fpv4-sp-d16 -mfloat-abi=hard -Tcubemx/STM32F429BITx_FLASH.ld -lc -lm -lnosys -Wl,-Map=build/cubemx.map,--cref -Wl,--gc-sections,-Bstatic -o build/cubemx.elf
/usr/local/crossgcc/arm-none-eabi/bin/arm-none-eabi-size build/cubemx.elf
text data bss dec hex filename
15084 24 20480 35588 8b04 build/cubemx.elf
/usr/local/crossgcc/arm-none-eabi/bin/arm-none-eabi-objcopy -O ihex build/cubemx.elf build/cubemx.hex
/usr/local/crossgcc/arm-none-eabi/bin/arm-none-eabi-objcopy -O binary -S build/cubemx.elf build/cubemx.bin
jw@bu201:/m/s/rep/git/test/src$ LANG= ldd build/cubemx.elf
not a dynamic executable
jw@bu201:/m/s/rep/git/test/src$
--
Josef Wolf
jw@raven.inka.de
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Linker won't bail out on non-existing functions?
2020-09-04 10:18 Linker won't bail out on non-existing functions? Josef Wolf
@ 2020-09-04 11:45 ` Alexander Monakov
2020-09-04 12:56 ` Josef Wolf
0 siblings, 1 reply; 3+ messages in thread
From: Alexander Monakov @ 2020-09-04 11:45 UTC (permalink / raw)
To: Josef Wolf; +Cc: gcc-help
On Fri, 4 Sep 2020, Josef Wolf wrote:
> So why won't the linker bail out when it can't resolve a reference?
> Any hints?
You're linking with --gc-sections, and if all references to undefined functions
are in discarded sections, the linker won't complain. In other words, checking
for remaining undefined references happens after discarding unneeded sections.
Alexander
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Linker won't bail out on non-existing functions?
2020-09-04 11:45 ` Alexander Monakov
@ 2020-09-04 12:56 ` Josef Wolf
0 siblings, 0 replies; 3+ messages in thread
From: Josef Wolf @ 2020-09-04 12:56 UTC (permalink / raw)
To: gcc-help
On Fri, Sep 04, 2020 at 02:45:04PM +0300, Alexander Monakov wrote:
> On Fri, 4 Sep 2020, Josef Wolf wrote:
>
> > So why won't the linker bail out when it can't resolve a reference?
> > Any hints?
>
> You're linking with --gc-sections, and if all references to undefined functions
> are in discarded sections, the linker won't complain. In other words, checking
> for remaining undefined references happens after discarding unneeded sections.
Thanks for the hint, Alexander!
the problem was that this function was used in a different task which was not
instantiated yet. =8-O
--
Josef Wolf
jw@raven.inka.de
^ permalink raw reply [flat|nested] 3+ messages in thread
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