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Chapter 13. ARM Dependent Features

.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.

13.5. Opcodes

as

implements all the standard ARM opcodes. It also implements several pseudo opcodes, including

several synthetic load instructions.

NOP

nop