Chapter 11. Alpha Dependent Features

79

.arch cpu

Specifies the target processor. This is equivalent to the

 mcpu

command line option. Options, for

a list of values for

cpu

.

.ent function[, n]

Mark the beginning of

function

. An optional number may follow for compatibility with the

OSF/1 assembler, but is ignored. When generating

.mdebug

information, this will create a pro 

cedure descriptor for the function. In ELF, it will mark the symbol as a function a la the generic

.type

directive.

.end function

Mark the end of

function

. In ELF, it will set the size of the symbol a la the generic

.size

directive.

.mask mask, offset

Indicate which of the integer registers are saved in the current function's stack frame.

mask

is

interpreted a bit mask in which bit

n

set indicates that register

n

is saved. The registers are saved

in a block located

offset

bytes from the canonical frame address (CFA) which is the value of

the stack pointer on entry to the function. The registers are saved sequentially, except that the

return address register (normally

$26

) is saved first.

This and the other directives that describe the stack frame are currently only used when generat 

ing

.mdebug

information. They may in the future be used to generate DWARF2

.debug_frame

unwind information for hand written assembly.

.fmask mask, offset

Indicate which of the floating point registers are saved in the current stack frame. The

mask

and

offset

parameters are interpreted as with

.mask

.

.frame framereg, frameoffset, retreg[, argoffset]

Describes the shape of the stack frame. The frame pointer in use is

framereg

; normally this is

either

$fp

or

$sp

. The frame pointer is

frameoffset

bytes below the CFA. The return address

is initially located in

retreg

until it is saved as indicated in

.mask

. For compatibility with

OSF/1 an optional

argoffset

parameter is accepted and ignored. It is believed to indicate the

offset from the CFA to the saved argument registers.

.prologue n

Indicate that the stack frame is set up and all registers have been spilled. The argument

n

indicates

whether and how the function uses the incoming procedure vector (the address of the called

function) in

$27

. 0 indicates that

$27

is not used; 1 indicates that the first two instructions of the

function use

$27

to perform a load of the GP register; 2 indicates that

$27

is used in some non 

standard way and so the linker cannot elide the load of the procedure vector during relaxation.

.usepv function, which

Used to indicate the use of the

$27

register, similar to

.prologue

, but without the other seman 

tics of needing to be inside an open

.ent

/

.end

block.

The

which

argument should be either

no

, indicating that

$27

is not used, or

std

, indicating that

the first two instructions of the function perform a GP load.

One might use this directive instead of

.prologue

if you are also using dwarf2 CFI directives.