Output section type (READONLY)

[Nick Clifton]

Hi Fangrui,

> For READONLY, I am thinking more in line with "whether we need this
> feature at all"... If no input has SHF_WRITE, the output naturally does
> not have SHF_WRITE; if an input has SHF_WRITE, chancing the output to
> non-SHF_WRITE is weird and error-prone.

I do not know if this counts as a *justified* use of READONLY, but it was
used recently in an attempt to add a new feature to Fedora rawhide:

   https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects#New_system:_.note.package

The feature used a custom linker script fragment to add a note section
into the executable being created, and this script used the READONLY
keyword:

   SECTIONS
   {
     .note.package (READONLY) : ALIGN(4) {
         BYTE(0x04) BYTE(0x00) BYTE(0x00) BYTE(0x00) /* Length of Owner including NUL */
  [...]
     }
   }
   INSERT AFTER .note.gnu.build-id;

This turned out to be problematic however as gold does not support the
READONLY attribute, nor the INSERT AFTER directive...

Anyway I think that the point here was that was no input section, so
the author needed another way to tell the linker that the output section
should be readonly.

Cheers
   Nick