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

A Type 3 image is similar to a Type 2 image except that the single load region is split into multiple root load regions.

The following figure shows the load and execution view for a Type 3 image without execute-only (XO) code:

Figure 3-6 Simple Type 3 image
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Use the following command for images of this type:

armlink --split --ro_base 0x8000 --rw_base 0xE000

Load view

In the load view, the first load region consists of the RO output section, and the second load region consists of the RW output section. The ZI output section does not exist at load time. It is created before execution, using the description of the output section contained in the image file.

Execution view

In the execution view, the first execution region contains the RO output section, the second execution region contains the RW output section, and the third execution region contains the ZI output section.

The execution address of the RO region is the same as its load address, so the contents of the RO output section do not have to be moved or copied from their load address to their execution address.

The execution address of the RW region is also the same as its load address, so the contents of the RW output section are not moved from their load address to their execution address. However, the ZI output section is created at run-time and is placed contiguously with the RW region.

Specify the load and execution address using the following linker options:

--ro_base address

Instructs armlink to set the load and execution address of the region containing the RO section at a four-byte aligned address, for example, the address of the first location in ROM. If you do not use the --ro_base option to specify the address, the default value of 0x8000 is used by armlink.

--rw_base address

Instructs armlink to set the execution address of the region containing the RW output section at a four-byte aligned address. If this option is used with --split, this specifies both the load and execution addresses of the RW region, for example, a root region.

--split

Splits the default single load region, that contains both the RO and RW output sections, into two root load regions:

  • One containing the RO output section.

  • One containing the RW output section.

You can then place them separately using --ro_base and --rw_base.

Load view for images containing XO sections

For images that contain XO sections, the XO output section is placed at the address specified by --ro_base. The RO and RW output sections are placed consecutively and immediately after the XO section.

If you use --split, then the one load region contains the XO and RO output sections, and the other contains the RW output section.

Execution view for images containing XO sections

For images that contain XO sections, the XO execution region is placed at the address specified by --ro_base. The RO execution region is placed contiguously and immediately after the XO execution region.

If you specify --split, then the XO and RO execution regions are placed in the first load region, and the RW and ZI execution regions are placed in the second load region.

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

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