arm-none-eabi-gcc -mcpu=cortex-m3 -mlittle-endian -mthumb -Wl,--gc-section -L _output/system_stm32f4xx.o (тут много много объектников) _output/beremizProcess.o _output/startup_stm32f407xx.o -o _output/beremizStm32Port.a -lstdc++

.\beremizStm32Port/./source/src/main.cpp:39: undefined reference to `initBeremizProcess()'

arm-none-eabi-ar -q -o _output/libBeremizStm32Port.a _output/system_stm32f4xx.o _output/syscalls.o  _output/startup_stm32f407xx.o ...далее длинный список всех остальных объектников для библиотеки...

"arm-none-eabi-gcc" "D:\_tmp\_beremiz2\build\plc_common_main.o" ...Все мои объектники для приложения... -o "D:\_tmp\_beremiz2\build\_beremiz2.elf" -L C:\Beremiz\beremiz\targets\STM32\port\BeremizStm32Port   -mcpu=cortex-m3 -mlittle-endian -mthumb -Wl,--gc-section  -T C:\Beremiz\beremiz\targets\STM32\port\STM32F407ZG_FLASH.ld

c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/bin/ld.exe: warning: cannot find entry symbol Reset_Handler; defaulting to 08000000
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libc.a(lib_a-sbrkr.o): In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0xc): undefined reference to `_sbrk'

arm-none-eabi-gcc mylib.a main.o -o main.elf

CFLAGS += -flto
...
ALL_CFLAGS += $(CFLAGS) ...

$(OBJDIR)/%.o : %.c makefile
    @echo $(MSG_COMPILING) $<
    $(CC) -c $(ALL_CFLAGS) $< -o $@

$(TARGET).elf: $(OBJ) | sizebefore
    @echo $(MSG_LINKING) $@
    $(CC) $(ALL_CFLAGS) $(OBJ) --output $@ $(LDFLAGS)

c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-abort.o): In function `abort':
abort.c:(.text.abort+0xa): undefined reference to `_exit'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-sbrkr.o): In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0xc): undefined reference to `_sbrk'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-signalr.o): In function `_kill_r':
signalr.c:(.text._kill_r+0xe): undefined reference to `_kill'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-signalr.o): In function `_getpid_r':
signalr.c:(.text._getpid_r+0x0): undefined reference to `_getpid'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-writer.o): In function `_write_r':
writer.c:(.text._write_r+0x10): undefined reference to `_write'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-closer.o): In function `_close_r':
closer.c:(.text._close_r+0xc): undefined reference to `_close'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-fstatr.o): In function `_fstat_r':
fstatr.c:(.text._fstat_r+0xe): undefined reference to `_fstat'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-isattyr.o): In function `_isatty_r':
isattyr.c:(.text._isatty_r+0xc): undefined reference to `_isatty'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-lseekr.o): In function `_lseek_r':
lseekr.c:(.text._lseek_r+0x10): undefined reference to `_lseek'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-readr.o): In function `_read_r':
readr.c:(.text._read_r+0x10): undefined reference to `_read'
collect2.exe: error: ld returned 1 exit status

#common flags
SET(COMMON_FLAGS "-mthumb")
SET(COMMON_FLAGS "${COMMON_FLAGS} -Wall")
SET(COMMON_FLAGS "${COMMON_FLAGS} -mcpu=cortex-m3")
SET(COMMON_FLAGS "${COMMON_FLAGS} -mlittle-endian")
#common compiler flags
SET(COMMON_CFLAGS "-D USE_STDPERIPH_DRIVER")
SET(COMMON_CFLAGS "${COMMON_CFLAGS} -D USE_STDPERIPH_DRIVER")
SET(COMMON_CFLAGS "${COMMON_CFLAGS} -D STM32F429_439xx")
#SET(COMMON_CFLAGS "${COMMON_CFLAGS} --specs=rdimon.specs")
#SET(COMMON_CFLAGS "${COMMON_CFLAGS} -Wl,--start-group -lgcc -lc -lm -lrdimon -Wl,--end-group")
#c-files compiler flags
SET(CMAKE_C_FLAGS "${COMMON_FLAGS} ${COMMON_CFLAGS}" CACHE INTERNAL "c compiler flags")
SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
#cpp-files compiler flags
SET(CMAKE_CXX_FLAGS "${COMMON_FLAGS} ${COMMON_CFLAGS}" CACHE INTERNAL "cxx compiler flags")
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g")
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-threadsafe-statics")
#linker flags
SET(CMAKE_EXE_LINKER_FLAGS "${COMMON_FLAGS}" CACHE INTERNAL "exe link flags")
SET(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--gc-section")
SET(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -T ./linkScript/STM32F407ZG_FLASH.ld")

LDFLAGS += --specs=nano.specs
LDFLAGS += --specs=nosys.specs

//=============================================================================
int __is_used fputc(int c, FILE* stream)
{
    dbg_putchar(c, stream);

    return (c);
}

//=============================================================================
int __is_used _write(int file, char *ptr, int len)
{
    (void)file;

    while (len--)
    {
        dbg_putchar(*ptr++, debug_stream);
    }

    return len;
}

-Wl,--start-group .... ... ... .... ... -Wl,--end-group