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(as.info)ESA/390 Directives

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ESA/390 Assembler Directives
----------------------------

   `as' for the ESA/390 supports all of the standard ELF/SVR4 assembler
directives that are documented in the main part of this documentation.
Several additional directives are supported in order to implement the
ESA/390 addressing model.  The most important of these are `.using' and
`.ltorg'

   These are the additional directives in `as' for the ESA/390:

`.dc'
     A small subset of the usual DC directive is supported.

`.drop REGNO'
     Stop using REGNO as the base register.  The REGNO must have been
     previously declared with a `.using' directive in the same section
     as the current section.

`.ebcdic STRING'
     Emit the EBCDIC equivalent of the indicated string.  The emitted
     string will be null terminated.  Note that the directives
     `.string' etc. emit ascii strings by default.

`EQU'
     The standard HLASM-style EQU directive is not supported; however,
     the standard `as' directive .equ can be used to the same effect.

`.ltorg'
     Dump the literal pool accumulated so far; begin a new literal pool.
     The literal pool will be written in the current section; in order
     to generate correct assembly, a `.using' must have been previously
     specified in the same section.

`.using EXPR,REGNO'
     Use REGNO as the base register for all subsequent RX, RS, and SS
     form instructions. The EXPR will be evaluated to obtain the base
     address; usually, EXPR will merely be `*'.

     This assembler allows two `.using' directives to be simultaneously
     outstanding, one in the `.text' section, and one in another section
     (typically, the `.data' section).  This feature allows dynamically
     loaded objects to be implemented in a relatively straightforward
     way.  A `.using' directive must always be specified in the `.text'
     section; this will specify the base register that will be used for
     branches in the `.text' section.  A second `.using' may be
     specified in another section; this will specify the base register
     that is used for non-label address literals.  When a second
     `.using' is specified, then the subsequent `.ltorg' must be put in
     the same section; otherwise an error will result.

     Thus, for example, the following code uses `r3' to address branch
     targets and `r4' to address the literal pool, which has been
     written to the `.data' section.  The is, the constants
     `=A(some_routine)', `=H'42'' and `=E'3.1416'' will all appear in
     the `.data' section.

          .data
          	.using  LITPOOL,r4
          .text
          	BASR	r3,0
          	.using	*,r3
                  B       START
          	.long	LITPOOL
          START:
          	L	r4,4(,r3)
          	L	r15,=A(some_routine)
          	LTR	r15,r15
          	BNE	LABEL
          	AH	r0,=H'42'
          LABEL:
          	ME	r6,=E'3.1416'
          .data
          LITPOOL:
          	.ltorg

     Note that this dual-`.using' directive semantics extends and is
     not compatible with HLASM semantics.  Note that this assembler
     directive does not support the full range of HLASM semantics.