ARM Machine Directives

.align expression [, expression]

This is the generic .align directive. For the ARM however if the first argument is zero (ie no alignment is needed) the assembler will behave as if the argument had been 2 (ie pad to the next four byte boundary). This is for compatibility with ARM's own assembler.

name .req register name

This creates an alias for register name called name. For example:

                  foo .req r0
          

.unreq alias-name

This undefines a register alias which was previously defined using the req directive. For example:

                  foo .req r0
                  .unreq foo
          

An error occurs if the name is undefined. Note - this pseudo op can be used to delete builtin in register name aliases (eg 'r0'). This should only be done if it is really necessary.

.code [16|32]

This directive selects the instruction set being generated. The value 16 selects Thumb, with the value 32 selecting ARM.

.thumb

This performs the same action as .code 16.

.arm

This performs the same action as .code 32.

.force_thumb

This directive forces the selection of Thumb instructions, even if the target processor does not support those instructions

.thumb_func

This directive specifies that the following symbol is the name of a Thumb encoded function. This information is necessary in order to allow the assembler and linker to generate correct code for interworking between Arm and Thumb instructions and should be used even if interworking is not going to be performed. The presence of this directive also implies .thumb

.thumb_set

This performs the equivalent of a .set directive in that it creates a symbol which is an alias for another symbol (possibly not yet defined). This directive also has the added property in that it marks the aliased symbol as being a thumb function entry point, in the same way that the .thumb_func directive does.

.ltorg

This directive causes the current contents of the literal pool to be dumped into the current section (which is assumed to be the .text section) at the current location (aligned to a word boundary). GAS maintains a separate literal pool for each section and each sub-section. The .ltorg directive will only affect the literal pool of the current section and sub-section. At the end of assembly all remaining, un-empty literal pools will automatically be dumped.

Note - older versions of GAS would dump the current literal pool any time a section change occurred. This is no longer done, since it prevents accurate control of the placement of literal pools.

.pool

This is a synonym for .ltorg.