在可执行文件中看不到链接库中的函数

Question

我正在尝试使用cmake为stm32f4编译FreeRTOS项目。除了链接syscalls.c之外，一切顺利。

项目结构如下：

不在src文件夹中的所有内容都被编译为静态库，即SPL，启动文件，FreeRTOS等。 我的上一个编译步骤：

[100%] Linking C executable bin/stm32f4_template.elf

/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/arm-none-eabi-gcc  
-mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 -march=armv7e-m -fsingle-precision-constant 
-finline-functions -Wdouble-promotion -std=gnu99 -Os -g -Wall -ffunction-sections 
-fdata-sections -specs=nano.specs -u _scanf_float -u printf_float -fno-exceptions 
-Wl,--gc-sections,-T/home/kript0n/Documents/projects/STM32F4-FreeRTOS/Utilities/stm32_flash.ld,
-Map,/home/kript0n/Documents/projects/STM32F4-FreeRTOS/build/bin/stm32f4_template.elf.map 
CMakeFiles/stm32f4_template.elf.dir/src/main.c.obj CMakeFiles/stm32f4_template.elf.dir/src/controller.c.obj  -o bin/stm32f4_template.elf 
Libraries/STM32F4xx_StdPeriph_Driver/libdriverlib.a FreeRTOS/libFreeRTOS.a hardware/libhardware.a -lm Libraries/TM/libtm.a Libraries/syscall/libsyscalls.a 

输出：

/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7e-m/fpu/libg_nano.a(lib_a-sbrkr.o): In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0xc): undefined reference to `_sbrk'
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7e-m/fpu/libg_nano.a(lib_a-writer.o): In function `_write_r':
writer.c:(.text._write_r+0x10): undefined reference to `_write'
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7e-m/fpu/libg_nano.a(lib_a-closer.o): In function `_close_r':
closer.c:(.text._close_r+0xc): undefined reference to `_close'
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7e-m/fpu/libg_nano.a(lib_a-fstatr.o): In function `_fstat_r':
fstatr.c:(.text._fstat_r+0xe): undefined reference to `_fstat'
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7e-m/fpu/libg_nano.a(lib_a-isattyr.o): In function `_isatty_r':
isattyr.c:(.text._isatty_r+0xc): undefined reference to `_isatty'
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7e-m/fpu/libg_nano.a(lib_a-lseekr.o): In function `_lseek_r':
lseekr.c:(.text._lseek_r+0x10): undefined reference to `_lseek'
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib/armv7e-m/fpu/libg_nano.a(lib_a-readr.o): In function `_read_r':
readr.c:(.text._read_r+0x10): undefined reference to `_read'
collect2: error: ld returned 1 exit status
CMakeFiles/stm32f4_template.elf.dir/build.make:126: recipe for target 'bin/stm32f4_template.elf' failed
make[2]: *** [bin/stm32f4_template.elf] Error 1

正如您所看到的，syscalls.c已链接，但仍未找到系统调用。这是syscalls.c的内容，所有缺少的函数都在里面显示：

#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>

#include "stdio.h"
#include "stm32f4xx_usart.h"

/***************************************************************************/

int _open(const char *name, int flags, int mode){
  return -1;
}

int _read(int file, char * ptr, int len) {
  ptr = ptr;
  len = len;
  errno = EINVAL;
  return -1;
}

/***************************************************************************/

int _lseek(int file, int ptr, int dir) {
  file = file;
  ptr = ptr;
  dir = dir;
  return 0;
}

/***************************************************************************/

int _write(int file, char * ptr, int len) {
  int index;
  if (!ptr) {
    return 0;
  }
  for (index = 0; index < len; index++) {
    while (!(USART3->SR & 0x00000040));
    USART_SendData(USART3, ptr[index]);
  }
  return len;
}

/***************************************************************************/

int _close(int file) {
  return 0;
}

/***************************************************************************/

/* Register name faking - works in collusion with the linker.  */
register char * stack_ptr asm ("sp");

caddr_t _sbrk(int incr) {
  extern char   end asm ("end"); // Defined by the linker.
  static char * heap_end;
  char *        prev_heap_end;
  if (heap_end == NULL)
    heap_end = & end;
  prev_heap_end = heap_end;
  if (heap_end + incr > stack_ptr) {
    // Some of the libstdc++-v3 tests rely upon detecting
    // out of memory errors, so do not abort here.
#if 0
    extern void abort (void);
    _write (1, "_sbrk: Heap and stack collision\n", 32);
    abort ();
#else
    errno = ENOMEM;
    return (caddr_t) -1;
#endif
  }
  heap_end += incr;
  return (caddr_t) prev_heap_end;
}

/***************************************************************************/

int _fstat(int file, struct stat * st) {
  file = file;
  memset (st, 0, sizeof (* st));
  st->st_mode = S_IFCHR;
  return 0;
}

/***************************************************************************/

int _isatty(int fd) {
  fd = fd;
  return 1;
}

int _kill(int pid, int sig) {
  errno=EINVAL;
  return(-1);
}

int _getpid(void) {
  return 1;
}

它的'建设步骤：

[ 85%] Building C object Libraries/syscall/CMakeFiles/syscalls.dir/syscalls.c.obj
cd /home/kript0n/Documents/projects/STM32F4-FreeRTOS/build/Libraries/syscall && /home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/arm-none-eabi-gcc  -DARM_MATH_CM4 -DHSE_VALUE=8000000 -DSTM32F40_41xxx -DSTM32F4XX -DUSESTD_PERIPH_DRIVER -D__FPU_PRESENT=1 -D__FPU_USED=1 -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/Libraries/CMSIS/Device/ST/STM32F4xx/Include -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/Libraries/CMSIS/Include -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/Libraries/STM32F4xx_StdPeriph_Driver/inc -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/Libraries/TM/TM_SPL -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/FreeRTOS/include -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/FreeRTOS/portable/GCC/ARM_CM4F -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/config -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/hardware -I/home/kript0n/Documents/projects/STM32F4-FreeRTOS/include  -mcpu=cortex-m4     -mthumb     -mfloat-abi=hard     -mfpu=fpv4-sp-d16     -march=armv7e-m     -fsingle-precision-constant     -finline-functions     -Wdouble-promotion     -std=gnu99     -Os     -g     -Wall     -ffunction-sections     -fdata-sections     -specs=nano.specs   -o CMakeFiles/syscalls.dir/syscalls.c.obj   -c /home/kript0n/Documents/projects/STM32F4-FreeRTOS/Libraries/syscall/syscalls.c
[ 89%] Linking C static library libsyscalls.a
cd /home/kript0n/Documents/projects/STM32F4-FreeRTOS/build/Libraries/syscall && /usr/bin/cmake -P CMakeFiles/syscalls.dir/cmake_clean_target.cmake
cd /home/kript0n/Documents/projects/STM32F4-FreeRTOS/build/Libraries/syscall && /usr/bin/cmake -E cmake_link_script CMakeFiles/syscalls.dir/link.txt --verbose=1
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/arm-none-eabi-ar qc libsyscalls.a  CMakeFiles/syscalls.dir/syscalls.c.obj
/home/kript0n/Applications/EmbeddedArm/gcc-arm-none-eabi-4_9-2015q2/bin/arm-none-eabi-ranlib libsyscalls.a
make[2]: Leaving directory '/home/kript0n/Documents/projects/STM32F4-FreeRTOS/build'
[ 89%] Built target syscalls

似乎文件被编译到库中，函数被呈现并且它被链接。那有什么不对呢？

谢谢！

Answer 1

确定将链接到哪个符号的规则，以及何时将它们标记为已使用但未被链接器删除的规则对于独立目标文件和库有些不同。通过仔细重新排列链接器命令行可能会纠正您的问题。

我已经停止关心它了，只是强行标记掉落的功能，并且使用了＆＃39;。

#define USED __attribute__ ((used))
#define UU __attribute__((unused))

int USED _close(int x UU) {
  return -1;
}

int USED _fstat(int file UU, struct stat *st) {
  st->st_mode = S_IFCHR;
  return 0;
}