3.6.5 Output Section Data

You can include explicit bytes of data in an output section by using BYTE, SHORT, LONG, QUAD, or SQUAD as an output section command. Each keyword is followed by an expression in parentheses providing the value to store (see Expressions). The value of the expression is stored at the current value of the location counter.

The BYTE, SHORT, LONG, and QUAD commands store one, two, four, and eight bytes (respectively). After storing the bytes, the location counter is incremented by the number of bytes stored.

For example, this will store the byte 1 followed by the four byte value of the symbol ‘addr’:

     BYTE(1)
     LONG(addr)

When using a 64 bit host or target, QUAD and SQUAD are the same; they both store an 8 byte, or 64 bit, value. When both host and target are 32 bits, an expression is computed as 32 bits. In this case QUAD stores a 32 bit value zero extended to 64 bits, and SQUAD stores a 32 bit value sign extended to 64 bits.

If the object file format of the output file has an explicit endianness, which is the normal case, the value will be stored in that endianness. When the object file format does not have an explicit endianness, as is true of, for example, S-records, the value will be stored in the endianness of the first input object file.

Note—these commands only work inside a section description and not between them, so the following will produce an error from the linker:

     SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } }

whereas this will work:

     SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } }

You may use the FILL command to set the fill pattern for the current section. It is followed by an expression in parentheses. Any otherwise unspecified regions of memory within the section (for example, gaps left due to the required alignment of input sections) are filled with the value of the expression, repeated as necessary. A FILL statement covers memory locations after the point at which it occurs in the section definition; by including more than one FILL statement, you can have different fill patterns in different parts of an output section.

This example shows how to fill unspecified regions of memory with the value ‘0x90’:

     FILL(0x90909090)

The FILL command is similar to the ‘=fillexp’ output section attribute, but it only affects the part of the section following the FILL command, rather than the entire section. If both are used, the FILL command takes precedence. See Output Section Fill, for details on the fill expression.