[Bug c++/106873] unsigned short skips byte when used for memory mapping depending on position in structure

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106873

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think you need to use bitfields to get this exact layout or use the attribute
packed.

With -Wpadded I get the following warnings:
<source>:19:17: warning: padding struct to align '<unnamed struct>::b'
[-Wpadded]
   19 |  unsigned short b;     //  2 bytes - skips one byte here
      |                 ^
<source>:17:1: warning: padding struct size to alignment boundary [-Wpadded]
   17 | {
      | ^
<source>:32:17: warning: padding struct to align '<unnamed struct>::e'
[-Wpadded]
   32 |  unsigned short e;     //  2 bytes - skips one byte here
      |                 ^
<source>:27:1: warning: padding struct size to alignment boundary [-Wpadded]
   27 | {
      | ^
<source>:39:17: warning: padding struct to align '<unnamed struct>::b'
[-Wpadded]
   39 |  unsigned short b;     //  2 bytes - skips one byte here
      |                 ^
<source>:41:17: warning: padding struct to align '<unnamed struct>::d'
[-Wpadded]
   41 |  unsigned short d;     //  2 bytes - skips one byte here
      |                 ^

Which I think is what you are missing is that the ABI is layed out this way.