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 in Linker Scripts). 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’:


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.

You can include a zero-terminated string in an output section by using ASCIZ. The keyword is followed by a string which is stored at the current value of the location counter adding a zero byte at the end. If the string includes spaces it must be enclosed in double quotes. The string may contain ’\n’, ’\r’, ’\t’ and octal numbers. Hex numbers are not supported.

For example, this string of 16 characters will create a 17 byte area

  ASCIZ "This is 16 bytes"

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’:


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.

Note - normally the value of expression is zero extended to 4 bytes when used to fill gaps. Thus ‘FILL(144)’ will fill a region with repeats of the pattern ‘0 0 0 144’. The value is treated as a big-endian number, so for example ‘FILL(22 * 256 + 23)’ will fill the region with repeats of the pattern ‘0 0 22 23’. If the expression results in a value with more than 4 significant bytes only the least 4 bytes of the value will be used.

The above rules do not apply when the expression is a simple hexadecimal number. In this case zero extension is not performed and all bytes are significant. So ‘FILL(0x90)’ will fill a region with repeats of ‘0x90’ with no zero bytes, and ‘FILL(0x9192)’ will fill the region with repeats of ‘0x91 0x92’. Zero bytes in a hexadecimal expression are significant even at the start, so ‘FILL(0x0090)’ will fill a region with repeats of ‘0x00 0x90’.

Hexadecimal numbers can be longer than 4 bytes, and all of the bytes are significant, so ‘FILL(0x123456789a)’ will fill a region with repeats of the 5 byte sequence ‘0x12 0x34 0x56 0x78 0x9a’. Excess bytes in a hexadecimal value beyond the size of a region will be silently ignored.

The above only applies to hexadecimal numbers specified as ‘0x[0-9][a-f][A-F]’. Hexadecimal numbers specified with a ‘$’ prefix, or a ‘h’, ‘H’, ‘x’ or ‘X’ suffix will follow the normal fill value rules. This also applies to expressions that involve hexadecimal numbers, and hexadecimal numbers that have a magnitude suffix.

The LINKER_VERSION command inserts a string containing the version of the linker at the current point. Note - by default this directive is disabled and will do nothing. It only becomes active if the --enable-linker-version command line option is used.

Built-in linker scripts for ELF based targets already include this directive in their ‘.comment’ section.