[Bug ld/14299] New: Allow output sections to be spread over multiple memory regions

[jifl-bugzilla at jifvik dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=14299

             Bug #: 14299
           Summary: Allow output sections to be spread over multiple
                    memory regions
           Product: binutils
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: ld
        AssignedTo: address@hidden
        ReportedBy: address@hidden
    Classification: Unclassified


This is an enhancement request. Memory controllers on embedded systems are
getting increasingly complex, yet still without an MMU. This can mean that on
some systems you can have some on-chip memory and some off-chip memory, but at
non-contiguous addresses. Or for example on the Cortex-M4 based Freescale
Kinetis, a region of on-chip SRAM which performs better for code, and the
remainder performs better for data; code and data can go in either, but isn't
cacheable in the "wrong" one.

It would be useful if the linker could allow for input sections to be able to
be spread over multiple output sections (located in specific MEMORY regions),
in a way that allows us to say: "first use this region, then only if that fills
up, use this other region".

I have no fixed idea of syntax, but as a starting point, how about wrapping
input sections with a special keyword, e.g.:
  ALLOW_MULTIPLE( <input section>, N ) where N is a number expressing the
priority so that sections are filled in the correct order. 
Here's an example:

MEMORY
  {
    ONCHIP : ORIGIN = 0x10000000, LENGTH=0x100000
    OFFCHIP : ORIGIN = 0x20000000, LENGTH=0x100000
  }
SECTIONS
  {
    .text { ALLOW_MULTIPLE( *(.data.*), 100 ) } > ONCHIP
    .textoffchip { ALLOW_MULTIPLE( *(.data.*), 200 ) } > OFFCHIP
    .data { ALLOW_MULTIPLE( *(.data.*), 100 ) } > ONCHIP
    .dataoffchip { ALLOW_MULTIPLE( *(.data.*), 200 ) } > OFFCHIP
  }

I think this would be very useful on quite a lot of embedded hardware, so
please consider it.

Thanks,

Jifl

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.