1@c Copyright (C) 2000-2016 Free Software Foundation, Inc. 2@c This is part of the GAS manual. 3@c For copying conditions, see the file as.texinfo. 4@ifset GENERIC 5@page 6@node ESA/390-Dependent 7@chapter ESA/390 Dependent Features 8@end ifset 9@ifclear GENERIC 10@node Machine Dependencies 11@chapter ESA/390 Dependent Features 12@end ifclear 13 14@cindex i370 support 15@cindex ESA/390 support 16 17@menu 18* ESA/390 Notes:: Notes 19* ESA/390 Options:: Options 20* ESA/390 Syntax:: Syntax 21* ESA/390 Floating Point:: Floating Point 22* ESA/390 Directives:: ESA/390 Machine Directives 23* ESA/390 Opcodes:: Opcodes 24@end menu 25 26@node ESA/390 Notes 27@section Notes 28The ESA/390 @code{@value{AS}} port is currently intended to be a back-end 29for the @sc{gnu} @sc{cc} compiler. It is not HLASM compatible, although 30it does support a subset of some of the HLASM directives. The only 31supported binary file format is ELF; none of the usual MVS/VM/OE/USS 32object file formats, such as ESD or XSD, are supported. 33 34When used with the @sc{gnu} @sc{cc} compiler, the ESA/390 @code{@value{AS}} 35will produce correct, fully relocated, functional binaries, and has been 36used to compile and execute large projects. However, many aspects should 37still be considered experimental; these include shared library support, 38dynamically loadable objects, and any relocation other than the 31-bit 39relocation. 40 41@node ESA/390 Options 42@section Options 43@code{@value{AS}} has no machine-dependent command-line options for the ESA/390. 44 45@cindex ESA/390 Syntax 46@node ESA/390 Syntax 47@section Syntax 48The opcode/operand syntax follows the ESA/390 Principles of Operation 49manual; assembler directives and general syntax are loosely based on the 50prevailing AT&T/SVR4/ELF/Solaris style notation. HLASM-style directives 51are @emph{not} supported for the most part, with the exception of those 52described herein. 53 54A leading dot in front of directives is optional, and the case of 55directives is ignored; thus for example, .using and USING have the same 56effect. 57 58A colon may immediately follow a label definition. This is 59simply for compatibility with how most assembly language programmers 60write code. 61 62@samp{#} is the line comment character. 63 64@samp{;} can be used instead of a newline to separate statements. 65 66Since @samp{$} has no special meaning, you may use it in symbol names. 67 68Registers can be given the symbolic names r0..r15, fp0, fp2, fp4, fp6. 69By using thesse symbolic names, @code{@value{AS}} can detect simple 70syntax errors. The name rarg or r.arg is a synonym for r11, rtca or r.tca 71for r12, sp, r.sp, dsa r.dsa for r13, lr or r.lr for r14, rbase or r.base 72for r3 and rpgt or r.pgt for r4. 73 74@samp{*} is the current location counter. Unlike @samp{.} it is always 75relative to the last USING directive. Note that this means that 76expressions cannot use multiplication, as any occurrence of @samp{*} 77will be interpreted as a location counter. 78 79All labels are relative to the last USING. Thus, branches to a label 80always imply the use of base+displacement. 81 82Many of the usual forms of address constants / address literals 83are supported. Thus, 84@example 85 .using *,r3 86 L r15,=A(some_routine) 87 LM r6,r7,=V(some_longlong_extern) 88 A r1,=F'12' 89 AH r0,=H'42' 90 ME r6,=E'3.1416' 91 MD r6,=D'3.14159265358979' 92 O r6,=XL4'cacad0d0' 93 .ltorg 94@end example 95should all behave as expected: that is, an entry in the literal 96pool will be created (or reused if it already exists), and the 97instruction operands will be the displacement into the literal pool 98using the current base register (as last declared with the @code{.using} 99directive). 100 101@node ESA/390 Floating Point 102@section Floating Point 103@cindex floating point, ESA/390 (@sc{ieee}) 104@cindex ESA/390 floating point (@sc{ieee}) 105The assembler generates only @sc{ieee} floating-point numbers. The older 106floating point formats are not supported. 107 108 109@node ESA/390 Directives 110@section ESA/390 Assembler Directives 111 112@code{@value{AS}} for the ESA/390 supports all of the standard ELF/SVR4 113assembler directives that are documented in the main part of this 114documentation. Several additional directives are supported in order 115to implement the ESA/390 addressing model. The most important of these 116are @code{.using} and @code{.ltorg} 117 118@cindex ESA/390-only directives 119These are the additional directives in @code{@value{AS}} for the ESA/390: 120 121@table @code 122@item .dc 123A small subset of the usual DC directive is supported. 124 125@item .drop @var{regno} 126Stop using @var{regno} as the base register. The @var{regno} must 127have been previously declared with a @code{.using} directive in the 128same section as the current section. 129 130@item .ebcdic @var{string} 131Emit the EBCDIC equivalent of the indicated string. The emitted string 132will be null terminated. Note that the directives @code{.string} etc. emit 133ascii strings by default. 134 135@item EQU 136The standard HLASM-style EQU directive is not supported; however, the 137standard @code{@value{AS}} directive .equ can be used to the same effect. 138 139@item .ltorg 140Dump the literal pool accumulated so far; begin a new literal pool. 141The literal pool will be written in the current section; in order to 142generate correct assembly, a @code{.using} must have been previously 143specified in the same section. 144 145@item .using @var{expr},@var{regno} 146Use @var{regno} as the base register for all subsequent RX, RS, and SS form 147instructions. The @var{expr} will be evaluated to obtain the base address; 148usually, @var{expr} will merely be @samp{*}. 149 150This assembler allows two @code{.using} directives to be simultaneously 151outstanding, one in the @code{.text} section, and one in another section 152(typically, the @code{.data} section). This feature allows 153dynamically loaded objects to be implemented in a relatively 154straightforward way. A @code{.using} directive must always be specified 155in the @code{.text} section; this will specify the base register that 156will be used for branches in the @code{.text} section. A second 157@code{.using} may be specified in another section; this will specify 158the base register that is used for non-label address literals. 159When a second @code{.using} is specified, then the subsequent 160@code{.ltorg} must be put in the same section; otherwise an error will 161result. 162 163Thus, for example, the following code uses @code{r3} to address branch 164targets and @code{r4} to address the literal pool, which has been written 165to the @code{.data} section. The is, the constants @code{=A(some_routine)}, 166@code{=H'42'} and @code{=E'3.1416'} will all appear in the @code{.data} 167section. 168 169@example 170.data 171 .using LITPOOL,r4 172.text 173 BASR r3,0 174 .using *,r3 175 B START 176 .long LITPOOL 177START: 178 L r4,4(,r3) 179 L r15,=A(some_routine) 180 LTR r15,r15 181 BNE LABEL 182 AH r0,=H'42' 183LABEL: 184 ME r6,=E'3.1416' 185.data 186LITPOOL: 187 .ltorg 188@end example 189 190 191Note that this dual-@code{.using} directive semantics extends 192and is not compatible with HLASM semantics. Note that this assembler 193directive does not support the full range of HLASM semantics. 194 195@end table 196 197@node ESA/390 Opcodes 198@section Opcodes 199For detailed information on the ESA/390 machine instruction set, see 200@cite{ESA/390 Principles of Operation} (IBM Publication Number DZ9AR004). 201