gcc-arm-none-eabi 11.3 "is not implemented and will always fail"

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I'm working on a bare-metal STM32 project, compiling on a Linux x64 host.

After upgrading my toolchain from gcc-arm-none-eabi-11.2-2022.02 to arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi, I get the following linker warnings:

warning: _close is not implemented and will always fail
warning: _fstat is not implemented and will always fail
warning: _getpid is not implemented and will always fail
warning: _isatty is not implemented and will always fail
warning: _kill is not implemented and will always fail
warning: _lseek is not implemented and will always fail
warning: _open is not implemented and will always fail
warning: _read is not implemented and will always fail
warning: _write is not implemented and will always fail

More comprehensively, I get this:

~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libg.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
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libc.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
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libc.a(libc_a-signalr.o): in function `_getpid_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/signalr.c:83: warning: _getpid is not implemented and will always fail
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libc.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
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libc.a(libc_a-signalr.o): in function `_kill_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/signalr.c:53: warning: _kill is not implemented and will always fail
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libg.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
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libc.a(libc_a-openr.o): in function `_open_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/openr.c:50: warning: _open is not implemented and will always fail
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libg.a(libc_a-readr.o): in function `_read_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/readr.c:49: warning: _read is not implemented and will always fail
~/dev_tools/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: ~/dev_tools/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/v7e-m+fp/hard/libg.a(libc_a-writer.o): in function `_write_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/writer.c:49: warning: _write is not implemented and will always fail

Other than that, the project seems to compile fine. Reading the release note (available here), I can't see what could cause this.

  1. What change caused this ?
  2. Can I disregard these warnings ? It looks like system calls, so I guess I can ?
  3. If so, can they be silenced ?
embedded stm32 gcc arm c
2 Answers

The library supplied with gcc-arm-none-eabi is called 'newlib'. You can download a copy from git://sourceware.org/git/newlib-cygwin.git. It has tags and you can determine the specific version released with your compiler and get the tagged version.

For example, syscalls.c is one implementation. The Libc stubs document contains functions to implement. However, you may wonder why you get these warnings. There are various 'C' library function calls, such as srand(), assert(), etc while will drag in the 'C' file libraries. You need to look at a map file and avoid these function calls if you wish to minimize overhead.

I am not sure of your code base and sub-sections of a map file would be helpful. Here you have,

  • _open_r
  • _close_r
  • _read_r

Which are from the 'reent' for re-entrant library. Typically, the re-entrant functions are only needed for an RTOS or desktop operating system. If you have a bare metal single main thread, you do not need these functions. You can not call open() in an interrupt handler with this option :) So, there is really only one context (and a single errno as well). The 're-entrant' functionality is useless. As is .fini sections, embedded devices don't 'shutdown' normally, they reboot.

What change caused this ?

You have linked with something (called a function) that brought in file system primitives in the 'C' library.

Can I disregard these warnings ?

It depends on your use case. Are you a safety critical system? Generally I would recommend fixing them so the next person is not confused. Most likely if the code follows the path to these functions, something is already wrong/unhandled.

It looks like system calls, so I guess I can?

Not a question?

If so, can they be silenced ?

Either avoid the functions or provide alternate implementations that 'do the right thing'. The 'right thing' will depend on your platform.

artless noise0

These are the methods that the system call needs to implement, you use the functions of the standard library (NEWLIB), so you should implement these methods according to your own platform If you're sure you don't need to implement these, just add an empty implementation to the link add link

void _close(void)
{
}
void _lseek(void)
{

}
void _read(void)
{
}
void _write(void)
{
}

before

[ 50%] Building C object CMakeFiles/xpad.dir/src/main.c.o
[100%] Linking C executable xpad
/home/wangkai/workspace/xpad/toolchain/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: /home/wangkai/workspace/xpad/toolchain/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/libc.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
/home/wangkai/workspace/xpad/toolchain/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: /home/wangkai/workspace/xpad/toolchain/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/libc.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
/home/wangkai/workspace/xpad/toolchain/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: /home/wangkai/workspace/xpad/toolchain/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/libc.a(libc_a-readr.o): in function `_read_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/readr.c:49: warning: _read is not implemented and will always fail
/home/wangkai/workspace/xpad/toolchain/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: /home/wangkai/workspace/xpad/toolchain/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/11.3.1/../../../../arm-none-eabi/lib/libc.a(libc_a-writer.o): in function `_write_r':
/data/jenkins/workspace/GNU-toolchain/arm-11/src/newlib-cygwin/newlib/libc/reent/writer.c:49: warning: _write is not implemented and will always fail
[100%] Built target xpad

after

[ 33%] Building C object CMakeFiles/xpad.dir/src/system_call.c.o
[ 66%] Linking C executable xpad
[100%] Built target xpad
wangkai0
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