[PATCH v2] Chapter-on-need-for-RTEMS-specific-cross-compiler

[Utkarsh Rai]

On Fri, Apr 3, 2020 at 8:15 AM Chris Johns <chrisj at rtems.org> wrote:

> On 2020-03-28 00:13, utkarsh.rai60 at gmail.com wrote:
> > ---
> >   user/start/tools.rst | 34 ++++++++++++++++++++++++++++++++++
> >   1 file changed, 34 insertions(+)
> >
> > diff --git a/user/start/tools.rst b/user/start/tools.rst
> > index c3f039b..8ea1f64 100644
> > --- a/user/start/tools.rst
> > +++ b/user/start/tools.rst
> > @@ -3,6 +3,7 @@
> >   .. Copyright (C) 2019 embedded brains GmbH
> >   .. Copyright (C) 2019 Sebastian Huber
> >   .. Copyright (C) 2020 Chris Johns
> > +.. Copyright (C) 2020 Utkarsh Rai
> >
> >   .. _QuickStartTools:
> >
> > @@ -76,3 +77,36 @@ source code used.
> >
> >
> >   Add ``--verbose`` to the GCC command for the the verbose version
> details.
> > +
> > +
> > +Need for RTEMS-Specific Cross-Compiler
> > +--------------------------------------------
>
> Length of ---'s does not match the heading.
>
> > +
> > +New users are often confused as to why they cannot use their
> distribution's
> > +cross-compiler for their target on rtems, e.g., the riscv64-linux-gnu
> or the
> > +arm-none-eabi-gcc on RTEMS. Below mentioned are some of the reasons for
> using
> > +the RTEMS cross-compiler.
> > +
> > + ``Correct configuration of Newlib -``
> > +     Newlib is a C standard library implementation intended for use on
> embedded
> > +     systems. Most of the POSIX and libc support for RTEMS is derived
> from
> > +     Newlib. The RTEMS cross-compiler configures Newlib correctly for
> RTEMS.
> > +
> > + ``Threading in GCC support libraries -``
> > +     Several threading packages in GCC such as Go threads (libgo),
> OpenMP
> > +     (libgomp), and OpenACC need to be customized according to RTEMS.
> This is
> > +     done by the RTEMS specific cross-compiler.
> > +
> > + ``Provide preprocessor define __rtems__ -``
> > +     The  ``__rtems__``  preprocessor define is used to provide
> conditional code
> > +     compilation in source files that are shared with other projects
> e.g. in
> > +     Newlib or imported code from FreeBSD.
> > +
> > + ``Multilib variants to match the BSP -``
> > +     RTEMS configures GCC to create separate runtime libraries for each
> > +     supported instruction set, floating point unit, vector unit, word
> size
> > +     (e.g. 32-bit and 64-bit), endianness, ABI, processor errata
> workarounds,
> > +     and so on in the architecture. These libraries are termed multilib
> variants
> > +     (
> https://docs.rtems.org/branches/master/user/hardware/architectures.html?highlight=multilib
> ).
>
> Please do not add external links to internal parts of the same document.
> Please use :ref: to do this. A link like this breaks on branches and PDFs.
>
> Would it be ok to just add reference to the architecture section of the
doc?

> Chris
>
> > +     Multilibs variants to match the BSP are set by selecting a
> specific set of
> > +     machine options using the RTEMS cross-compiler.
> >
>
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