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Chapter 42. Xtensa Dependent Features

there are no preceding

ENTRY

instructions or

.literal_position

directives, the assembler will

print a warning and place the literal pool at the beginning of the current section. In such cases,

explicit

.literal_position

directives should be used to place the literal pools.

42.5.6. literal_position

When using

 text section literals

to place literals inline in the section being assembled, the

.literal_position

directive can be used to mark a potential location for a literal pool.

.literal_position

The

.literal_position

directive is ignored when the

 text section literals

option is not

used.

The assembler will automatically place text section literal pools before

ENTRY

instructions, so the

.literal_position

directive is only needed to specify some other location for a literal pool. You

may need to add an explicit jump instruction to skip over an inline literal pool.

For example, an interrupt vector does not begin with an

ENTRY

instruction so the assembler will be

unable to automatically find a good place to put a literal pool. Moreover, the code for the interrupt

vector must be at a specific starting address, so the literal pool cannot come before the start of the

code. The literal pool for the vector must be explicitly positioned in the middle of the vector (before

any uses of the literals, of course). The

.literal_position

directive can be used to do this. In

the following code, the literal for

M

will automatically be aligned correctly and is placed after the

unconditional jump.

.global M

code_start:

j continue

.literal_position

.align 4

continue:

movi

a4, M

42.5.7. literal_prefix

The

literal_prefix

directive allows you to specify different sections to hold literals from different

portions of an assembly file. With this directive, a single assembly file can be used to generate code

into multiple sections, including literals generated by the assembler.

.begin literal_prefix [name]

.end literal_prefix

For the code inside the delimited region, the assembler puts literals in the section

name.literal

. If

this section does not yet exist, the assembler creates it. The

name

parameter is optional. If

name

is not

specified, the literal prefix is set to the "default" for the file. This default is usually

.literal

but can

be changed with the

 rename section

command line argument.