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

[utkarsh.rai60 at gmail.com]

---
 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
+--------------------------------------------
+
+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).
+     Multilibs variants to match the BSP are set by selecting a specific set of
+     machine options using the RTEMS cross-compiler.
-- 
2.17.1