7.13.4 Type 3 image, multiple load regions and non-contiguous execution regions

A Type 3 image consists of multiple load regions in load view and multiple execution regions in execution view. They are similar to images of Type 2 except that the single load region in Type 2 is now split into multiple load regions.

You can relocate and split load regions using the following linker options:

--reloc
The combination --reloc --split makes an image similar to simple Type 3, but the two load regions now have the RELOC attribute.
--ro_base=address1
Specifies the load and execution address of the region containing the RO output section.
--rw_base=address2
Specifies the load and execution address for the region containing the RW output section.
--xo_base=address3
Specifies the load and execution address for the region containing the execute-only (XO) output section, if present.
--split
Splits the default single load region that contains the RO and RW output sections into two load regions. One load region contains the RO output section and one contains the RW output section.

Note:

For images containing XO sections, and if --xo_base is not used, an XO execution region is placed at the address specified by --ro_base. The RO execution region is placed immediately after the XO region.

Example for multiple load regions

The following example shows the scatter-loading description equivalent to using --ro_base=0x010000 --rw_base=0x040000 --split:

LR_1 0x010000     ; The first load region is at 0x010000.
{    
    ER_RO +0      ; The address is 0x010000.
    {
        * (+RO)
    }
}
LR_2 0x040000     ; The second load region is at 0x040000.
{
    ER_RW +0      ; The address is 0x040000.
    {
        * (+RW)   ; All RW sections are placed consecutively into this region.
    }
    ER_ZI +0      ; The address is 0x040000 + size of ER_RW region.
    {
        * (+ZI)   ; All ZI sections are placed consecutively into this region.
    }
}

In this example:

  • This description creates an image with two load regions, named LR_1 and LR_2, that have load addresses 0x010000 and 0x040000.
  • The image has three execution regions, named ER_RO, ER_RW and ER_ZI, that contain the RO, RW, and ZI output sections respectively. The execution address of ER_RO is 0x010000.
  • The ER_RW execution region is not contiguous with ER_RO, because its execution address is 0x040000.
  • The ER_ZI execution region is placed immediately after ER_RW.

Example for multiple load regions with an XO region

The following example shows the scatter-loading description equivalent to using --ro_base=0x010000 --rw_base=0x040000 --split when an object file has XO sections:

LR_1 0x010000     ; The first load region is at 0x010000.
{    
    ER_XO +0      ; The address is 0x010000.
    {
        * (+XO)
    }
    ER_RO +0      ; The address is 0x010000 + size of ER_XO region.
    {
        * (+RO)
    }
}
LR_2 0x040000     ; The second load region is at 0x040000.
{
    ER_RW +0      ; The address is 0x040000.
    {
        * (+RW)   ; All RW sections are placed consecutively into this region.
    }
    ER_ZI +0      ; The address is 0x040000 + size of ER_RW region.
    {
        * (+ZI)   ; All ZI sections are placed consecutively into this region.
    }
}

In this example:

  • This description creates an image with two load regions, named LR_1 and LR_2, that have load addresses 0x010000 and 0x040000.
  • The image has four execution regions, named ER_XO, ER_RO, ER_RW and ER_ZI, that contain the XO, RO, RW, and ZI output sections respectively. The execution address of ER_XO is placed at the address specified by --ro_base, 0x010000. ER_RO is placed immediately after ER_XO.
  • The ER_RW execution region is not contiguous with ER_RO, because its execution address is 0x040000.
  • The ER_ZI execution region is placed immediately after ER_RW.

Note:

If you also specify --xo_base, then the ER_XO execution region is placed in a load region separate from the ER_RO execution region, at the specified address.

Relocatable load regions example variant

This Type 3 image also consists of two load regions in load view and three execution regions in execution view. However, --reloc specifies that the two load regions now have the RELOC attribute.

The following example shows the scatter-loading description equivalent to using --ro_base 0x010000 --rw_base 0x040000 --reloc --split:

LR_1 0x010000 RELOC
{
     ER_RO + 0
     {
         * (+RO)
     }
} 
LR2 0x040000 RELOC
{
     ER_RW + 0
     {
         * (+RW)
     }
     ER_ZI +0
     { 
         * (+ZI)
     }
}
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