SPRU513Z August 2001 – October 2023 SM320F28335-EP
As with align, you can tell the linker to place an output section at an address that falls on an n-byte boundary, where n is a power of 2, by using the palign keyword. In addition, palign ensures that the size of the section is a multiple of its placement alignment restrictions, padding the section size up to such a boundary, as needed.
For example, the following code lines allocate .text on a 2-byte boundary within the PMEM area. The .text section size is guaranteed to be a multiple of 2 bytes. Both statements are equivalent:
.text: palign(2) {} > PMEM
.text: palign = 2 {} > PMEMIf the linker adds padding to an initialized output section then the padding space is also initialized. By default, padding space is filled with a value of 0 (zero). However, if a fill value is specified for the output section then any padding for the section is also filled with that fill value. For example, consider the following section specification:
.mytext: palign(8), fill = 0xffff {} > PMEMIn this example, the length of the .mytext section is 3 16-bit bytes before the palign operator is applied. The contents of .mytext are as follows:
addr content
---- -------
0001 0x1234
0002 0x1234
0003 0x1234After the palign operator is applied, the length of .mytext is 8 bytes, and its contents are as follows:
addr content
---- -------
0001 0x1234
0002 0x1234
0003 0x1234
0004 0xffff
0005 0xffff
0006 0xffff
0007 0xffffThe size of .mytext has been bumped to a multiple of 8 bytes and the padding created by the linker has been filled with 0xff.
The fill value specified in the linker command file is interpreted as a 16-bit constant. If you specify this code:
.mytext: palign(8), fill = 0xff {} > PMEMThe fill value assumed by the linker is 0x00ff, and .mytext will then have the following contents:
addr content
---- -------
0001 0x1234
0002 0x1234
0003 0x1234
0004 0x00ff
0005 0x00ff
0006 0x00ff
0007 0x00ffIf the palign operator is applied to an uninitialized section, then the size of the section is bumped to the appropriate boundary, as needed, but any padding created is not initialized.
The palign operator can also take a parameter of power2. This parameter tells the linker to add padding to increase the section's size to the next power of two boundary. In addition, the section is aligned on that power of 2 as well. For example, consider the following section specification:
.mytext: palign(power2) {} > PMEMAssume that the size of the .mytext section is 120 bytes and PMEM starts at address 0x10020. After applying the palign(power2) operator, the .mytext output section will have the following properties:
name addr size align
------- ---------- ----- -----
.mytext 0x00010080 0x80 128