Digging a bit, I noticed a huge block of <cmath> is ifdef'ed out for
aarch64.
I found the file c++config.h which is different between the two.

Based on the diff of the arm and aarch64 versions, arm has
 _GLIBCXX_USE_C99_MATH_TR1 defined but aarch64 does not.

I have no idea where the settings in this file come from but this
appears to be the key difference.

More insight appreciated.

=====================================================
round]$ diff
 /home/joel/rtems-work/tools/6/lib/gcc/arm-rtems6/12.2.1/include/c++/arm-rtems6/bits/c++config.h
/home/joel/rtems-work/tools/6/lib/gcc/aarch64-rtems6/12.2.1/include/c++/aarch64-rtems6/bits/c++config.h
886c886
< /* #undef _GLIBCXX_HAVE_ATOMIC_LOCK_POLICY */
---
> #define _GLIBCXX_HAVE_ATOMIC_LOCK_POLICY 1
1702c1702
< #define _GLIBCXX_MANGLE_SIZE_T j
---
> #define _GLIBCXX_MANGLE_SIZE_T m
1711c1711
< #define _GLIBCXX_PTRDIFF_T_IS_INT 1
---
> /* #undef _GLIBCXX_PTRDIFF_T_IS_INT */
1717c1717
< #define _GLIBCXX_SIZE_T_IS_UINT 1
---
> /* #undef _GLIBCXX_SIZE_T_IS_UINT */
1774c1774
< #define _GLIBCXX_USE_C99_MATH_TR1 1
---
> /* #undef _GLIBCXX_USE_C99_MATH_TR1 */
=====================================================


On Mon, Nov 7, 2022 at 11:28 AM Richard Earnshaw <
Richard.Earnshaw@foss.arm.com> wrote:

>
>
> On 03/11/2022 14:13, Joel Sherrill wrote:
> > Hi
> >
> > This is likely not a newlib bug but I thought I would start here because
> > I'm not sure what is going on and I thought someone on this list would
> have
> > an idea: This is a simple C++ function that calls std::round. It compiles
> > on arm but aarch64 says round isn't in the std namespace.
> >
> > If you change the program to just use round() and not std::round() it
> > compiles on both architectures.
> >
> > The compiler versions are the same and report:
> >
> > arm-rtems6-gcc (GCC) 12.2.1 20221014 (RTEMS 6, RSB
> > cb8821e93378118e78a9cb25859789b126bd5761, Newlib 0b6342c)
> >
> > =====================
> > $ cat r.cc
> > #include <cmath>
> >
> >
> >
> > int wrap(double v)
> >
> > {
> >
> >    double r = std::round((float)v);
> >
> >    return (r > 0);
> >
> > }
> >
> > [joel@devel round]$ arm-rtems6-gcc -Wall -c r.cc
> > [joel@devel round]$ aarch64-rtems6-gcc -Wall -c r.cc
> > r.cc: In function 'int wrap(double)':
> > r.cc:5:19: error: 'round' is not a member of 'std'; did you mean 'round'?
> >      5 |   double r = std::round((float)v);
> >        |                   ^~~~~
> > In file included from
> >
> /home/joel/rtems-work/tools/6/lib/gcc/aarch64-rtems6/12.2.1/include/c++/cmath:45,
> >                   from r.cc:1:
> > /home/joel/rtems-work/tools/6/aarch64-rtems6/include/math.h:337:15: note:
> > 'round' declared here
> >    337 | extern double round (double);
> > =====================
> >
> > Any ideas what would cause this?
> >
> > Thanks
> >
> > --joel
>
> Have you tried comparing the pre-processed output from the two versions?
>   It might give a clue as to what's going on.
>
> R.
>