Re: Correct usage of nosys

I am calling printf and I have an implementation of `_write` (in the same
file that I attempted to add `_fstat`) that works.

I already produce the map file for other purposes. How do I use that to see
the "call trees"?


- Niklas


On Tue, 18 Feb 2025 at 12:54, Richard Earnshaw (lists) <
[email protected]> wrote:

> On 18/02/2025 08:18, Niklas Dusenlund wrote:
> > 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/lib/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/lib/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/bin/ld:
> /usr/local/bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/lib/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/lib/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/lib/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/lib/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
>
> _fstat_r is the low-level implementation of fstat (), but something else
> is probably calling that.
>
> This can happen if there is a chain of function calls from your code to
> this function.  To find out why you'll need to get the linker to produce a
> map file with -Map=<file>.  The map will show which function was called
> that resulted in _fstat_r being needed and you can then recurse back to
> find which function in your code needed something that resulted in that.
>
> Are you, for example, calling printf somewhere, or using an assert?
>
> R.
>