GCC Arm 11.3rel1, 12.2编译提示 _close is not implemented and will always fail

使用GCC Arm工具链开发的项目, 在11.2下编译正常, 但是升级到 arm-gnu-toolchain-11.3.rel1 以及 arm-gnu-toolchain-12.2 之后, 编译出现警告

/opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/bin/ld: /opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libc_nano.a(libc_a-closer.o): in function `_close_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/closer.c:47: warning: _close is not implemented and will always fail
/opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/bin/ld: /opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libc_nano.a(libc_a-fstatr.o): in function `_fstat_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/fstatr.c:55: warning: _fstat is not implemented and will always fail
/opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/bin/ld: /opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libc_nano.a(libc_a-isattyr.o): in function `_isatty_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/isattyr.c:52: warning: _isatty is not implemented and will always fail
/opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/bin/ld: /opt/gcc-arm/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libc_nano.a(libc_a-lseekr.o): in function `_lseek_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/lseekr.c:49: warning: _lseek is not implemented and will always fail

这是因为使用了printf, 定义了 int _read(int file, char *ptr, int len)和int _write(int file, char *ptr, int len)方法但是未定义其它方法所致.

一个完整的输入输出重定向需要包含以下函数, 把剩下的都补齐就不会提示警告了

int _isatty(int fd);
int _write(int fd, char* ptr, int len);
int _close(int fd);
int _lseek(int fd, int ptr, int dir);
int _read(int fd, char* ptr, int len);
int _fstat(int fd, struct stat* st);

首先引入必要的头文件

#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>

然后是固定的方法

__attribute__((weak)) int _isatty(int fd)
{
    if (fd >= STDIN_FILENO && fd <= STDERR_FILENO)
        return 1;

    errno = EBADF;
    return 0;
}

__attribute__((weak)) int _close(int fd)
{
    if (fd >= STDIN_FILENO && fd <= STDERR_FILENO)
        return 0;

    errno = EBADF;
    return -1;
}

__attribute__((weak)) int _lseek(int fd, int ptr, int dir)
{
    (void)fd;
    (void)ptr;
    (void)dir;

    errno = EBADF;
    return -1;
}

__attribute__((weak)) int _fstat(int fd, struct stat *st)
{
    if (fd >= STDIN_FILENO && fd <= STDERR_FILENO)
    {
        st->st_mode = S_IFCHR;
        return 0;
    }

    errno = EBADF;
    return 0;
}

_read 和 _write 是与底层硬件实现相关的, 需要自己实现对应的字符输入和输出

__attribute__((weak)) int _read(int file, char *ptr, int len)
{
    (void)file;
    int DataIdx;
    for (DataIdx = 0; DataIdx < len; DataIdx++)
    {
        *ptr++ = __io_getchar();
    }
    return len;
}

__attribute__((weak)) int _write(int file, char *ptr, int len)
{
    (void)file;
    int DataIdx;
    for (DataIdx = 0; DataIdx < len; DataIdx++)
    {
        __io_putchar(*ptr++);
    }
    return len;
}