RFA: Allow .rdata to be writable on mips-wrs-vxworks

[Richard Sandiford]

Ping.

Richard Sandiford <richard@codesourcery.com> writes:
> The VxWorks libraries use .rdata as the read-only data section.
> The linker normally places it as an orphan next to .rodata, and
> things work as expected.
>
> Unfortunately, one of the objects in libdl.a has a _writable_ .rdata
> section.  The orphan placement code creates the .rdata output section
> statement when it finds the first input .rdata section, and this first
> input section will usually be read-only.  The code therefore places
> the output section statement on the assumption that it too will be
> read-only, so we then end up with a writable text segment.
>
> This was always less than ideal, but worked.  However, in older
> binutils, the data segment was aligned to 0x40000 -- much greater than
> MAXPAGESIZE -- and so we would usually still have 2 segments.  The data
> segment is now aligned only to MAXPAGESIZE (which seems like a good thing)
> and so we end up with a single RWE segment.  This appears to crash the
> loader.  (It also screws up the calculation of DT_TEXTREL, and I wondered
> at first if that was causing the loader problem.  Forcing DT_TEXTREL to be
> added didn't cure the crash though.)
>
> Although binutils could probably cope more gracefully with this situation,
> I don't want to clutter it with target-independent workarounds for what is
> basically an OS bug.  I'd therefore like to apply the VxWorks-specific
> patch below.
>
> Tested on mips-wrs-vxworks.  OK to install?
>
> Richard
>
>
> ld/
> 	* emulparams/elf32ebmipvxworks.sh (OTHER_READONLY_SECTIONS)
> 	(OTHER_READWRITE_SECTIONS): Define.  Add .rdata sections.
>
> Index: ld/emulparams/elf32ebmipvxworks.sh
> ===================================================================
> RCS file: /cvs/src/src/ld/emulparams/elf32ebmipvxworks.sh,v
> retrieving revision 1.1
> diff -u -p -r1.1 elf32ebmipvxworks.sh
> --- ld/emulparams/elf32ebmipvxworks.sh	22 Mar 2006 09:28:13 -0000	1.1
> +++ ld/emulparams/elf32ebmipvxworks.sh	14 May 2007 12:53:04 -0000
> @@ -3,6 +3,15 @@
>  OUTPUT_FORMAT="elf32-bigmips-vxworks"
>  BIG_OUTPUT_FORMAT="elf32-bigmips-vxworks"
>  LITTLE_OUTPUT_FORMAT="elf32-littlemips-vxworks"
> +# VxWorks .rdata sections are normally read-only, but one of the objects
> +# in libdl.a (the dynamic loader) is actually read-write.  Explicitly
> +# place the section in the appropriate segment for its flags.
> +OTHER_READONLY_SECTIONS="
> +  .rdata ${RELOCATING-0} : ONLY_IF_RO { *(.rdata) }
> +"
> +OTHER_READWRITE_SECTIONS="
> +  .rdata ${RELOCATING-0} : ONLY_IF_RW { *(.rdata) }
> +"
>  unset OTHER_GOT_SYMBOLS
>  SHLIB_TEXT_START_ADDR=0
>  unset TEXT_DYNAMIC