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+@c Copyright 2000, 2002 Free Software Foundation, Inc.
+@c This is part of the GAS manual.
+@c For copying conditions, see the file as.texinfo.
+@ifset GENERIC
+@page
+@node ESA/390-Dependent
+@chapter ESA/390 Dependent Features
+@end ifset
+@ifclear GENERIC
+@node Machine Dependencies
+@chapter ESA/390 Dependent Features
+@end ifclear
+
+@cindex i370 support
+@cindex ESA/390 support
+
+@menu
+* ESA/390 Notes:: Notes
+* ESA/390 Options:: Options
+* ESA/390 Syntax:: Syntax
+* ESA/390 Floating Point:: Floating Point
+* ESA/390 Directives:: ESA/390 Machine Directives
+* ESA/390 Opcodes:: Opcodes
+@end menu
+
+@node ESA/390 Notes
+@section Notes
+The ESA/390 @code{@value{AS}} port is currently intended to be a back-end
+for the @sc{gnu} @sc{cc} compiler. It is not HLASM compatible, although
+it does support a subset of some of the HLASM directives. The only
+supported binary file format is ELF; none of the usual MVS/VM/OE/USS
+object file formats, such as ESD or XSD, are supported.
+
+When used with the @sc{gnu} @sc{cc} compiler, the ESA/390 @code{@value{AS}}
+will produce correct, fully relocated, functional binaries, and has been
+used to compile and execute large projects. However, many aspects should
+still be considered experimental; these include shared library support,
+dynamically loadable objects, and any relocation other than the 31-bit
+relocation.
+
+@node ESA/390 Options
+@section Options
+@code{@value{AS}} has no machine-dependent command-line options for the ESA/390.
+
+@cindex ESA/390 Syntax
+@node ESA/390 Syntax
+@section Syntax
+The opcode/operand syntax follows the ESA/390 Principles of Operation
+manual; assembler directives and general syntax are loosely based on the
+prevailing AT&T/SVR4/ELF/Solaris style notation. HLASM-style directives
+are @emph{not} supported for the most part, with the exception of those
+described herein.
+
+A leading dot in front of directives is optional, and the case of
+directives is ignored; thus for example, .using and USING have the same
+effect.
+
+A colon may immediately follow a label definition. This is
+simply for compatibility with how most assembly language programmers
+write code.
+
+@samp{#} is the line comment character.
+
+@samp{;} can be used instead of a newline to separate statements.
+
+Since @samp{$} has no special meaning, you may use it in symbol names.
+
+Registers can be given the symbolic names r0..r15, fp0, fp2, fp4, fp6.
+By using thesse symbolic names, @code{@value{AS}} can detect simple
+syntax errors. The name rarg or r.arg is a synonym for r11, rtca or r.tca
+for r12, sp, r.sp, dsa r.dsa for r13, lr or r.lr for r14, rbase or r.base
+for r3 and rpgt or r.pgt for r4.
+
+@samp{*} is the current location counter. Unlike @samp{.} it is always
+relative to the last USING directive. Note that this means that
+expressions cannot use multiplication, as any occurrence of @samp{*}
+will be interpreted as a location counter.
+
+All labels are relative to the last USING. Thus, branches to a label
+always imply the use of base+displacement.
+
+Many of the usual forms of address constants / address literals
+are supported. Thus,
+@example
+ .using *,r3
+ L r15,=A(some_routine)
+ LM r6,r7,=V(some_longlong_extern)
+ A r1,=F'12'
+ AH r0,=H'42'
+ ME r6,=E'3.1416'
+ MD r6,=D'3.14159265358979'
+ O r6,=XL4'cacad0d0'
+ .ltorg
+@end example
+should all behave as expected: that is, an entry in the literal
+pool will be created (or reused if it already exists), and the
+instruction operands will be the displacement into the literal pool
+using the current base register (as last declared with the @code{.using}
+directive).
+
+@node ESA/390 Floating Point
+@section Floating Point
+@cindex floating point, ESA/390 (@sc{ieee})
+@cindex ESA/390 floating point (@sc{ieee})
+The assembler generates only @sc{ieee} floating-point numbers. The older
+floating point formats are not supported.
+
+
+@node ESA/390 Directives
+@section ESA/390 Assembler Directives
+
+@code{@value{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 @code{.using} and @code{.ltorg}
+
+@cindex ESA/390-only directives
+These are the additional directives in @code{@value{AS}} for the ESA/390:
+
+@table @code
+@item .dc
+A small subset of the usual DC directive is supported.
+
+@item .drop @var{regno}
+Stop using @var{regno} as the base register. The @var{regno} must
+have been previously declared with a @code{.using} directive in the
+same section as the current section.
+
+@item .ebcdic @var{string}
+Emit the EBCDIC equivalent of the indicated string. The emitted string
+will be null terminated. Note that the directives @code{.string} etc. emit
+ascii strings by default.
+
+@item EQU
+The standard HLASM-style EQU directive is not supported; however, the
+standard @code{@value{AS}} directive .equ can be used to the same effect.
+
+@item .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 @code{.using} must have been previously
+specified in the same section.
+
+@item .using @var{expr},@var{regno}
+Use @var{regno} as the base register for all subsequent RX, RS, and SS form
+instructions. The @var{expr} will be evaluated to obtain the base address;
+usually, @var{expr} will merely be @samp{*}.
+
+This assembler allows two @code{.using} directives to be simultaneously
+outstanding, one in the @code{.text} section, and one in another section
+(typically, the @code{.data} section). This feature allows
+dynamically loaded objects to be implemented in a relatively
+straightforward way. A @code{.using} directive must always be specified
+in the @code{.text} section; this will specify the base register that
+will be used for branches in the @code{.text} section. A second
+@code{.using} may be specified in another section; this will specify
+the base register that is used for non-label address literals.
+When a second @code{.using} is specified, then the subsequent
+@code{.ltorg} must be put in the same section; otherwise an error will
+result.
+
+Thus, for example, the following code uses @code{r3} to address branch
+targets and @code{r4} to address the literal pool, which has been written
+to the @code{.data} section. The is, the constants @code{=A(some_routine)},
+@code{=H'42'} and @code{=E'3.1416'} will all appear in the @code{.data}
+section.
+
+@example
+.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
+@end example
+
+
+Note that this dual-@code{.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.
+
+@end table
+
+@node ESA/390 Opcodes
+@section Opcodes
+For detailed information on the ESA/390 machine instruction set, see
+@cite{ESA/390 Principles of Operation} (IBM Publication Number DZ9AR004).