HPPA Dependent Features
***********************

Notes
=====

As a back end for GNU CC AS has been throughly tested and should work extremely well.  We have tested it only minimally on hand written assembly code and no one has tested it much on the assembly output from the HP compilers.

The format of the debugging sections has changed since the original AS port (version 1.3X) was released; therefore, you must rebuild all HPPA objects and libraries with the new assembler so that you can debug the final executable.

The HPPA AS port generates a small subset of the relocations available in the SOM and ELF object file formats.  Additional relocation support will be added as it becomes necessary.

Options
=======

AS has no machine-dependent command-line options for the HPPA.

Syntax
======

The assembler syntax closely follows the HPPA instruction set reference manual; assembler directives and general syntax closely follow the HPPA assembly language reference manual, with a few noteworthy differences.

First, a colon may immediately follow a label definition.  This is simply for compatibility with how most assembly language programmers write code.

Some obscure expression parsing problems may affect hand written code which uses the spop instructions, or code which makes significant use of the ! line separator.

AS is much less forgiving about missing arguments and other similar oversights than the HP assembler.  AS notifies you of missing arguments as syntax errors; this is regarded as a feature, not a bug.

Finally, AS allows you to use an external symbol without explicitly importing the symbol.  Warning: in the future this will be an error for HPPA targets.

Special characters for HPPA targets include:

; is the line comment character.

! can be used instead of a newline to separate statements.

Since $ has no special meaning, you may use it in symbol names.

Floating Point
==============

The HPPA family uses IEEE floating-point numbers.

HPPA Assembler Directives
=========================

AS for the HPPA supports many additional directives for compatibility with the native assembler.  This section describes them only briefly.  For detailed information on HPPA-specific assembler directives, see HP9000 Series 800 Assembly Language Reference Manual (HP 92432-90001).

AS does not support the following assembler directives described in the HP manual:

     .endm           .liston
     .enter          .locct
     .leave          .macro
     .listoff

Beyond those implemented for compatibility, AS supports one additional assembler directive for the HPPA: .param.  It conveys register argument locations for static functions.  Its syntax closely follows the .export directive.

These are the additional directives in AS for the HPPA:

.block N
.blockz N
     Reserve N bytes of storage, and initialize them to zero.

.call
     Mark the beginning of a procedure call.  Only the special case with no arguments is allowed.

.callinfo [ PARAM=VALUE, ... ]  [ FLAG, ... ]
     Specify a number of parameters and flags that define the environment for a procedure.

     PARAM may be any of frame (frame size), entry_gr (end of general register range), entry_fr (end of float register range), entry_sr (end of space register range).

     The values for FLAG are calls or caller (proc has subroutines), no_calls (proc does not call subroutines), save_rp (preserve return pointer), save_sp (proc preserves stack pointer), no_unwind (do not unwind this proc), hpux_int (proc is interrupt routine).

.code
     Assemble into the standard section called $TEXT$, subsection $CODE$.

.enter
     Not yet supported; the assembler rejects programs containing this directive.

.entry
     Mark the beginning of a procedure.

.exit
     Mark the end of a procedure.

.export NAME [ ,TYP ]  [ ,PARAM=R ]
     Make a procedure NAME available to callers.  TYP, if present, must be one of absolute, code (ELF only, not SOM), data, entry, data, entry, millicode, plabel, pri_prog, or sec_prog.

     PARAM, if present, provides either relocation information for the procedure arguments and result, or a privilege level.  PARAM may be argwN (where N ranges from 0 to 3, and indicates one of four one-word arguments); rtnval (the procedure's result); or priv_lev (privilege level).  For arguments or the result, R specifies how to relocate, and must be one of no (not relocatable), gr (argument is in general register), fr (in floating point register), or fu (upper half of float register). For priv_lev, R is an integer.

.half N
     Define a two-byte integer constant N; synonym for the portable AS directive .short.

.import NAME [ ,TYP ]
     Converse of .export; make a procedure available to call.  The arguments use the same conventions as the first two arguments for .export.

.label NAME
     Define NAME as a label for the current assembly location.

.leave
     Not yet supported; the assembler rejects programs containing this directive.

.origin LC
     Advance location counter to LC. Synonym for the as portable directive .org.

.param NAME [ ,TYP ]  [ ,PARAM=R ]
     Similar to .export, but used for static procedures.

.proc
     Use preceding the first statement of a procedure.

.procend
     Use following the last statement of a procedure.

LABEL .reg EXPR
     Synonym for .equ; define LABEL with the absolute expression EXPR as its value.

.space SECNAME [ ,PARAMS ]
     Switch to section SECNAME, creating a new section by that name if necessary.  You may only use PARAMS when creating a new section, not when switching to an existing one.  SECNAME may identify a section by number rather than by name.

     If specified, the list PARAMS declares attributes of the section, identified by keywords.  The keywords recognized are spnum=EXP (identify this section by the number EXP, an absolute expression), sort=EXP (order sections according to this sort key when linking; EXP is an absolute expression), unloadable (section contains no loadable data), notdefined (this section defined elsewhere), and private (data in this section not available to other programs).

.spnum SECNAM
     Allocate four bytes of storage, and initialize them with the section number of the section named SECNAM.  (You can define the section number with the HPPA .space directive.)

.string "STR"
     Copy the characters in the string STR to the object file. See Strings, for information on escape sequences you can use in AS strings.

     Warning! The HPPA version of .string differs from the usual AS definition: it does not write a zero byte after copying STR.

.stringz "STR"
     Like .string, but appends a zero byte after copying STR to object file.

.subspa NAME [ ,PARAMS ]

.nsubspa NAME [ ,PARAMS ]
     Similar to .space, but selects a subsection NAME within the current section.  You may only specify PARAMS when you create a subsection (in the first instance of .subspa for this NAME).

     If specified, the list PARAMS declares attributes of the subsection, identified by keywords.  The keywords recognized are quad=EXPR (``quadrant'' for this subsection), align=EXPR (alignment for beginning of this subsection; a power of two), access=EXPR (value for ``access rights'' field), sort=EXPR (sorting order for this subspace in link), code_only (subsection contains only code), unloadable (subsection cannot be loaded into memory), common (subsection is common block), dup_comm (initialized data may have duplicate names), or zero (subsection is all zeros, do not write in object file).

     .nsubspa always creates a new subspace with the given name, even if one with the same name already exists.

.version "STR"
     Write STR as version identifier in object code.

Opcodes
=======

For detailed information on the HPPA machine instruction set, see PA-RISC Architecture and Instruction Set Reference Manual (HP 09740-90039).