SLAU131V October   2004  – February 2020

 

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8.5.5.7 Automatic Splitting of Output Sections Among Non-Contiguous Memory Ranges

The linker can split output sections among multiple memory ranges for efficient allocation. Use the >> operator to indicate that an output section can be split, if necessary, into the specified memory ranges:

MEMORY { P_MEM1 : origin = 0x2000, length = 0x1000 P_MEM2 : origin = 0x4000, length = 0x1000 P_MEM3 : origin = 0x6000, length = 0x1000 P_MEM4 : origin = 0x8000, length = 0x1000 } SECTIONS { .text: { *(.text) } >> P_MEM1 | P_MEM2 | P_MEM3 | P_MEM4 }

In this example, the >> operator indicates that the .text output section can be split among any of the listed memory areas. If the .text section grows beyond the available memory in P_MEM1, it is split on an input section boundary, and the remainder of the output section is allocated to P_MEM2 | P_MEM3 | P_MEM4.

The | operator is used to specify the list of multiple memory ranges.

You can also use the >> operator to indicate that an output section can be split within a single memory range. This functionality is useful when several output sections must be allocated into the same memory range, but the restrictions of one output section cause the memory range to be partitioned. Consider the following example:

MEMORY { RAM : origin = 0x1000, length = 0x8000 } SECTIONS { .special: { f1.c.obj(.text) } load = 0x4000 .text: { *(.text) } >> RAM }

The .special output section is allocated near the middle of the RAM memory range. This leaves two unused areas in RAM: from 0x1000 to 0x4000, and from the end of f1.c.obj(.text) to 0x8000. The specification for the .text section allows the linker to split the .text section around the .special section and use the available space in RAM on either side of .special.

The >> operator can also be used to split an output section among all memory ranges that match a specified attribute combination. For example:

MEMORY { P_MEM1 (RWX) : origin = 0x1000, length = 0x2000 P_MEM2 (RWI) : origin = 0x4000, length = 0x1000 } SECTIONS { .text: { *(.text) } >> (RW) }

The linker attempts to allocate all or part of the output section into any memory range whose attributes match the attributes specified in the SECTIONS directive.

This SECTIONS directive has the same effect as:

SECTIONS { .text: { *(.text) } >> P_MEM1 | P_MEM2} }

Certain sections should not be split:

  • Certain sections created by the compiler, including
    • The .cinit section, which contains the autoinitialization table for C/C++ programs
    • The .pinit section, which contains the list of global constructors for C++ programs
  • An output section with an input section specification that includes an expression to be evaluated. The expression may define a symbol that is used in the program to manage the output section at run time.
  • An output section that has a START(), END(), OR SIZE() operator applied to it. These operators provide information about a section's load or run address, and size. Splitting the section may compromise the integrity of the operation.
  • The run allocation of a UNION. (Splitting the load allocation of a UNION is allowed.)

If you use the >> operator on any of these sections, the linker issues a warning and ignores the operator.