Re: Building newlib with clock_gettime()

RTEMS has a robust set of clock services and its own clock_gettime
implementation. We do use some FreeBSD kernel level time code which reduces
contention for time in SMP systems and integrates well with NTP and PTP.
Both of which we have solid support for.

https://gitlab.rtems.org/rtems/rtos/rtems/-/blob/main/cpukit/posix/src/clockgettime.c?ref_type=heads

I checked and the symbol clock_gettime isn't in the built libc.a .

Not that any of this impacts your explanation. clock_gettime is just one of
the methods that may need to be implemented in a target specific way. RTEMS
adds a lot ofPOSIX not in newlib and has its own Malloc family
implementation, for example.

--joel

On Wed, Jan 8, 2025 at 3:43 PM Jeff Johnston <[email protected]> wrote:

> Hello,
>
> Newlib does not provide an implementation for clock_gettime().  In glibc,
> for example, the source code uses syscalls to implement this which are not
> part of the standard newlib syscall set.  Some platforms may define
> clock_gettime() stubs that simply fail (RTEMS for example).  If you just
> need to satisfy a link requirement, you can easily create such a stub that
> fails, otherwise, you will have to implement the function yourself or try
> to port an implementation from another library (e.g. FreeBSD).
>
> -- Jeff J.
>
> On Mon, Jan 6, 2025 at 5:32 PM Caden <[email protected]> wrote:
>
>> Hi!
>>
>> I'm trying to build a RISC-V GNU compiler with *clock_gettime()*
>> provided by newlib. It seems that building the toolchain by default does
>> *not* enable this function -- looking at the libstdc++ library config
>> settings shows that any symbols regarding *clock_gettime()* are disabled
>> *.*
>>
>> I'm wondering if there's anything specific that can be done to have this
>> function provided by newlib.
>> Here's the command that newlib was built with:
>>
>> $  /nobackup/build/riscv-gnu-toolchain/newlib/configure
>> --target=riscv64-unknown-elf --prefix=/nobackup/build/riscv64-unknown-elf
>> --enable-newlib-io-long-double --enable-newlib-io-long-long
>> --enable-newlib-io-c99-formats
>> --enable-newlib-reigster-fini CFLAGS_FOR_TARGET=-O2 -D_POSIX_MODE
>> -ffunction-sections -fdata-sections    -mcmodel=medlow
>> CXXFLAGS_FOR_TARGET=-O2 -D_POSIX_MODE -ffunction-sections -fdata-sections
>>   -mcmodel=medlow
>>
>> Thanks!
>>
>