Correct usage of nosys

Hi Niklas,

what you're describing looks good, I'm currently doing it exactly that way 
with the most recent toolchain and newlib.

The functions you observe (_fstat, ...) are a basic set of syscalls that you 
might want to provide to adapt newlib to your platform/board/processor/
environment. A bit of information about this is
- https://sourceware.org/newlib/libc.html#Syscalls and
- a bit is here: https://sourceware.org/newlib/libgloss.html#Libc

When you use `--specs=nosys.specs` it will link against `libnosys` from 
`libgloss` (find it in libgloss/libnosys/) that provides stubs for these 
functions. They usually 'fail', that is, do nothing and return an error. Also 
they are attributed so that the compiler emits a symbol in a special section 
(`.gnu.warning....` for gcc IIRC) that hints a recent linker to emit the 
warnings you're seeing ('not implemented and will always fail').

Can you reduce your project to a minimum code example and show the command 
lines you use for compilation and linking?
Something seems to be off there.

Kind regards,
Sven


Am Dienstag, 18. Februar 2025, 09:18:47 CET schrieb Niklas Dusenlund:
> Hi!
> 
> I'm compiling for ARM cortex-m0. When I enable the nosys specs I get the
> following warnings:
> 
> ```
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin
> /ld:
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/li
> b/libc_nano.a(libc_a-fstatr.o): in function `_fstat_r':
> fstatr.c:(.text._fstat_r+0x1c): warning: _fstat is not implemented and will
> always fail
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin
> /ld:
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/li
> b/libc_nano.a(libc_a-fstatr.o): note: the message above does not take linker
> garbage collection into account
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bi
> n/ld:
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/li
> b/libc_nano.a(libc_a-isattyr.o): in function `_isatty_r':
> isattyr.c:(.text._isatty_r+0x18): warning: _isatty is not implemented and
> will always fail
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin
> /ld:
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/li
> b/libc_nano.a(libc_a-isattyr.o): note: the message above does not take
> linker garbage collection into account ```
> 
> I have no intention of using fstat or isatty. But if I implement the
> missing functions like this:
> 
> ```
> int _fstat(int fildes, struct stat *st) {
>   errno = ENOSYS;
>   return -1;
> }
> int _isatty(int file) { return -1; }
> ```
> 
> I get the following errors:
> 
> ```
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin
> /ld:
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/li
> b/libc_nano.a(libc_a-isattyr.o): in function `_isatty_r':
> isattyr.c:(.text._isatty_r+0x18): undefined reference to `_isatty'
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin
> /ld:
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/li
> b/libc_nano.a(libc_a-fstatr.o): in function `_fstat_r':
> fstatr.c:(.text._fstat_r+0x1c): undefined reference to `_fstat'
> ```
> 
> If I remove the nosys specs I also get undefined references to _exit and
> _sbrk.
> 
> In older versions of newlib I could use nano+nosys without warnings. What
> is the appropriate way with the latest newlib? If I need to link in my own
> stubs, how do I actually do that?
> 
> - Niklas
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