[PATCH v2 2/2] docs/misra: add Rule 5.1

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>

Add Rule 5.1, with the additional note that the character limit for Xen
is 40 characters.

The max length identifiers found by ECLAIR are:

__mitigate_spectre_bhb_clear_insn_start
domain_pause_by_systemcontroller_nosync

Both of them are 40 characters long.

Explicitly mention that public headers might have longer identifiers.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
---

Changes in v2:
- lower the limit to 40
- mention public headers
- improve commit message
---
 docs/misra/rules.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/docs/misra/rules.rst b/docs/misra/rules.rst
index 7d6a9fe063..6ccff07765 100644
--- a/docs/misra/rules.rst
+++ b/docs/misra/rules.rst
@@ -82,6 +82,13 @@ existing codebase are work-in-progress.
      - Line-splicing shall not be used in // comments
      -
 
+   * - `Rule 5.1 
<https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_01_2.c>`_
+     - Required
+     - External identifiers shall be distinct
+     - The Xen characters limit for identifiers is 40. Public headers
+       (xen/include/public/) are allowed to retain longer identifiers
+       for backward compatibility.
+
    * - `Rule 6.2 
<https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_06_02.c>`_
      - Required
      - Single-bit named bit fields shall not be of a signed type
-- 
2.25.1