201 lines
7.0 KiB
Plaintext
201 lines
7.0 KiB
Plaintext
@c Copyright (C) 2000 Free Software Foundation, Inc.
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@c This is part of the GAS manual.
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@c For copying conditions, see the file as.texinfo.
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@ifset GENERIC
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@page
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@node ESA/390-Dependent
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@chapter ESA/390 Dependent Features
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@end ifset
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@ifclear GENERIC
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@node Machine Dependencies
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@chapter ESA/390 Dependent Features
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@end ifclear
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@cindex i370 support
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@cindex ESA/390 support
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@menu
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* ESA/390 Notes:: Notes
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* ESA/390 Options:: Options
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* ESA/390 Syntax:: Syntax
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* ESA/390 Floating Point:: Floating Point
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* ESA/390 Directives:: ESA/390 Machine Directives
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* ESA/390 Opcodes:: Opcodes
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@end menu
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@node ESA/390 Notes
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@section Notes
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The ESA/390 @code{@value{AS}} port is currently intended to be a back-end
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for the @sc{gnu} @sc{cc} compiler. It is not HLASM compatible, although
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it does support a subset of some of the HLASM directives. The only
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supported binary file format is ELF; none of the usual MVS/VM/OE/USS
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object file formats, such as ESD or XSD, are supported.
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When used with the @sc{gnu} @sc{cc} compiler, the ESA/390 @code{@value{AS}}
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will produce correct, fully relocated, functional binaries, and has been
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used to compile and execute large projects. However, many aspects should
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still be considered experimental; these include shared library support,
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dynamically loadable objects, and any relocation other than the 31-bit
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relocation.
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@node ESA/390 Options
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@section Options
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@code{@value{AS}} has no machine-dependent command-line options for the ESA/390.
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@cindex ESA/390 Syntax
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@node ESA/390 Syntax
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@section Syntax
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The opcode/operand syntax follows the ESA/390 Principles of Operation
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manual; assembler directives and general syntax are loosely based on the
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prevailing AT&T/SVR4/ELF/Solaris style notation. HLASM-style directives
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are @emph{not} supported for the most part, with the exception of those
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described herein.
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A leading dot in front of directives is optional, and the case of
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directives is ignored; thus for example, .using and USING have the same
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effect.
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A colon may immediately follow a label definition. This is
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simply for compatibility with how most assembly language programmers
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write code.
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@samp{#} is the line comment character.
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@samp{;} can be used instead of a newline to separate statements.
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Since @samp{$} has no special meaning, you may use it in symbol names.
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Registers can be given the symbolic names r0..r15, fp0, fp2, fp4, fp6.
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By using thesse symbolic names, @code{@value{AS}} can detect simple
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syntax errors. The name rarg or r.arg is a synonym for r11, rtca or r.tca
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for r12, sp, r.sp, dsa r.dsa for r13, lr or r.lr for r14, rbase or r.base
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for r3 and rpgt or r.pgt for r4.
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@samp{*} is the current location counter. Unlike @samp{.} it is always
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relative to the last USING directive. Note that this means that
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expressions cannot use multiplication, as any occurence of @samp{*}
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will be interpreted as a location counter.
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All labels are relative to the last USING. Thus, branches to a label
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always imply the use of base+displacement.
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Many of the usual forms of address constants / address literals
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are supported. Thus,
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@example
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.using *,r3
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L r15,=A(some_routine)
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LM r6,r7,=V(some_longlong_extern)
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A r1,=F'12'
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AH r0,=H'42'
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ME r6,=E'3.1416'
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MD r6,=D'3.14159265358979'
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O r6,=XL4'cacad0d0'
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.ltorg
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@end example
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should all behave as expected: that is, an entry in the literal
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pool will be created (or reused if it already exists), and the
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instruction operands will be the displacement into the literal pool
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using the current base register (as last declared with the @code{.using}
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directive).
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@node ESA/390 Floating Point
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@section Floating Point
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@cindex floating point, ESA/390 (@sc{ieee})
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@cindex ESA/390 floating point (@sc{ieee})
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The assembler generates only @sc{ieee} floating-point numbers. The older
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floiating point formats are not supported.
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@node ESA/390 Directives
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@section ESA/390 Assembler Directives
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@code{@value{AS}} for the ESA/390 supports all of the standard ELF/SVR4
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assembler directives that are documented in the main part of this
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documentation. Several additional directives are supported in order
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to implement the ESA/390 addressing model. The most important of these
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are @code{.using} and @code{.ltorg}
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@cindex ESA/390-only directives
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These are the additional directives in @code{@value{AS}} for the ESA/390:
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@table @code
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@item .dc
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A small subset of the usual DC directive is supported.
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@item .drop @var{regno}
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Stop using @var{regno} as the base register. The @var{regno} must
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have been previously declared with a @code{.using} directive in the
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same section as the current section.
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@item .ebcdic @var{string}
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Emit the EBCDIC equivalent of the indicated string. The emitted string
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will be null terminated. Note that the directives @code{.string} etc. emit
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ascii strings by default.
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@item EQU
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The standard HLASM-style EQU directive is not supported; however, the
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standard @code{@value{AS}} directive .equ can be used to the same effect.
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@item .ltorg
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Dump the literal pool accumulated so far; begin a new literal pool.
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The literal pool will be written in the current section; in order to
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generate correct assembly, a @code{.using} must have been previously
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specified in the same section.
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@item .using @var{expr},@var{regno}
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Use @var{regno} as the base register for all subsequent RX, RS, and SS form
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instructions. The @var{expr} will be evaluated to obtain the base address;
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usually, @var{expr} will merely be @samp{*}.
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This assembler allows two @code{.using} directives to be simultaneously
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outstanding, one in the @code{.text} section, and one in another section
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(typically, the @code{.data} section). This feature allows
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dynamically loaded objects to be implemented in a relatively
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straightforward way. A @code{.using} directive must always be specified
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in the @code{.text} section; this will specify the base register that
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will be used for branches in the @code{.text} section. A second
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@code{.using} may be specified in another section; this will specify
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the base register that is used for non-label address literals.
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When a second @code{.using} is specified, then the subsequent
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@code{.ltorg} must be put in the same section; otherwise an error will
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result.
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Thus, for example, the following code uses @code{r3} to address branch
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targets and @code{r4} to address the literal pool, which has been written
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to the @code{.data} section. The is, the constants @code{=A(some_routine)},
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@code{=H'42'} and @code{=E'3.1416'} will all appear in the @code{.data}
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section.
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@example
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.data
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.using LITPOOL,r4
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.text
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BASR r3,0
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.using *,r3
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B START
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.long LITPOOL
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START:
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L r4,4(,r3)
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L r15,=A(some_routine)
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LTR r15,r15
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BNE LABEL
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AH r0,=H'42'
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LABEL:
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ME r6,=E'3.1416'
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.data
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LITPOOL:
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.ltorg
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@end example
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Note that this dual-@code{.using} directive semantics extends
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and is not compatible with HLASM semantics. Note that this assembler
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directive does not support the full range of HLASM semantics.
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@end table
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@node ESA/390 Opcodes
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@section Opcodes
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For detailed information on the ESA/390 machine instruction set, see
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@cite{ESA/390 Principles of Operation} (IBM Publication Number DZ9AR004).
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