as: Alpha Directives
9.2.5 Alpha Assembler Directives
--------------------------------
'as' for the Alpha supports many additional directives for compatibility
with the native assembler. This section describes them only briefly.
These are the additional directives in 'as' for the Alpha:
'.arch CPU'
Specifies the target processor. This is equivalent to the '-mCPU'
command-line option. 
Options Alpha 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 procedure
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 '$26') is saved first.
This and the other directives that describe the stack frame are
currently only used when generating '.mdebug' information. They
may in the future be used to generate DWARF2 '.debug_frame' unwind
information for hand written assembly.
'.fmask MASK, OFFSET'
Indicate which of the floating-point registers are saved in the
current stack frame. The MASK and OFFSET parameters are
interpreted as with '.mask'.
'.frame FRAMEREG, FRAMEOFFSET, RETREG[, ARGOFFSET]'
Describes the shape of the stack frame. The frame pointer in use
is FRAMEREG; normally this is either '$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 semantics of needing to be
inside an open '.ent'/'.end' block.
The WHICH argument should be either 'no', indicating that '$27' is
not used, or 'std', indicating that the first two instructions of
the function perform a GP load.
One might use this directive instead of '.prologue' if you are also
using dwarf2 CFI directives.
'.gprel32 EXPRESSION'
Computes the difference between the address in EXPRESSION and the
GP for the current object file, and stores it in 4 bytes. In
addition to being smaller than a full 8 byte address, this also
does not require a dynamic relocation when used in a shared
library.
'.t_floating EXPRESSION'
Stores EXPRESSION as an IEEE double precision value.
'.s_floating EXPRESSION'
Stores EXPRESSION as an IEEE single precision value.
'.f_floating EXPRESSION'
Stores EXPRESSION as a VAX F format value.
'.g_floating EXPRESSION'
Stores EXPRESSION as a VAX G format value.
'.d_floating EXPRESSION'
Stores EXPRESSION as a VAX D format value.
'.set FEATURE'
Enables or disables various assembler features. Using the positive
name of the feature enables while using 'noFEATURE' disables.
'at'
Indicates that macro expansions may clobber the "assembler
temporary" ('$at' or '$28') register. Some macros may not be
expanded without this and will generate an error message if
'noat' is in effect. When 'at' is in effect, a warning will
be generated if '$at' is used by the programmer.
'macro'
Enables the expansion of macro instructions. Note that
variants of real instructions, such as 'br label' vs 'br
$31,label' are considered alternate forms and not macros.
'move'
'reorder'
'volatile'
These control whether and how the assembler may re-order
instructions. Accepted for compatibility with the OSF/1
assembler, but 'as' does not do instruction scheduling, so
these features are ignored.
The following directives are recognized for compatibility with the
OSF/1 assembler but are ignored.
.proc .aproc
.reguse .livereg
.option .aent
.ugen .eflag
.alias .noalias
Info Catalog
as: Alpha Floating Point
as: Alpha-Dependent
as: Alpha Opcodes