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Preface Arm Compiler Tools Overview armclang Reference armlink Reference fromelf Reference armar Reference armasm Legacy Assembler Reference armasm Command-line Options --16 --32 --apcs=qualifier…qualifier --arm --arm_only --bi --bigend --brief_diagnostics, --no_brief_diagnostics --checkreglist --cpreproc --cpreproc_opts=option[,option,…] --cpu=list (armasm) --cpu=name (armasm) --debug --depend=dependfile --depend_format=string --diag_error=tag[,tag,…] (armasm) --diag_remark=tag[,tag,…] (armasm) --diag_style={arm|ide|gnu} (armasm) --diag_suppress=tag[,tag,…] (armasm) --diag_warning=tag[,tag,…] (armasm) --dllexport_all --dwarf2 --dwarf3 --errors=errorfile --exceptions, --no_exceptions --exceptions_unwind, --no_exceptions_unwind --execstack, --no_execstack --execute_only --fpmode=model --fpu=list (armasm) --fpu=name (armasm) -g (armasm) --help (armasm) -idir[,dir, …] --keep (armasm) --length=n --li --library_type=lib --list=file --list= --littleend -m (armasm) --maxcache=n --md --no_code_gen --no_esc --no_hide_all --no_regs --no_terse --no_warn -o filename (armasm) --pd --predefine "directive" --reduce_paths, --no_reduce_paths --regnames --report-if-not-wysiwyg --show_cmdline (armasm) --thumb --unaligned_access, --no_unaligned_access --unsafe --untyped_local_labels --version_number (armasm) --via=filename (armasm) --vsn (armasm) --width=n --xref Structure of armasm Assembly Language Modules Syntax of source lines in armasm syntax assembly l Literals ELF sections and the AREA directive An example armasm syntax assembly language module Writing A32/T32 Instructions in armasm Syntax Asse About the Unified Assembler Language Syntax differences between UAL and A64 assembly la Register usage in subroutine calls Load immediate values Load immediate values using MOV and MVN Load immediate values using MOV32 Load immediate values using LDR Rd, =const Literal pools Load addresses into registers Load addresses to a register using ADR Load addresses to a register using ADRL Load addresses to a register using LDR Rd, =label Other ways to load and store registers Load and store multiple register instructions Load and store multiple register instructions in A Stack implementation using LDM and STM Stack operations for nested subroutines Block copy with LDM and STM Memory accesses The Read-Modify-Write operation Optional hash with immediate constants Use of macros Test-and-branch macro example Unsigned integer division macro example Instruction and directive relocations Symbol versions Frame directives Exception tables and Unwind tables Using armasm armasm command-line syntax Specify command-line options with an environment v Using stdin to input source code to the assembler Built-in variables and constants Identifying versions of armasm in source code Diagnostic messages Interlocks diagnostics Automatic IT block generation in T32 code T32 branch target alignment T32 code size diagnostics A32 and T32 instruction portability diagnostics T32 instruction width diagnostics Two pass assembler diagnostics Using the C preprocessor Address alignment in A32/T32 code Address alignment in A64 code Instruction width selection in T32 code Symbols, Literals, Expressions, and Operators in a Symbol naming rules Variables Numeric constants Assembly time substitution of variables Register-relative and PC-relative expressions Labels Labels for PC-relative addresses Labels for register-relative addresses Labels for absolute addresses Numeric local labels Syntax of numeric local labels String expressions String literals Numeric expressions Syntax of numeric literals Syntax of floating-point literals Logical expressions Logical literals Unary operators Binary operators Multiplicative operators String manipulation operators Shift operators Addition, subtraction, and logical operators Relational operators Boolean operators Operator precedence Difference between operator precedence in assembly armasm Directives Reference Alphabetical list of directives armasm assembly la About armasm assembly language control directives About frame directives Directives that can be omitted in pass 2 of the as ALIAS ALIGN AREA ARM or CODE32 directive ASSERT ATTR CN CODE16 directive COMMON CP DATA DCB DCD and DCDU DCDO DCFD and DCFDU DCFS and DCFSU DCI DCQ and DCQU DCW and DCWU END ENDFUNC or ENDP ENTRY EQU EXPORT or GLOBAL EXPORTAS FIELD FRAME ADDRESS FRAME POP FRAME PUSH FRAME REGISTER FRAME RESTORE FRAME RETURN ADDRESS FRAME SAVE FRAME STATE REMEMBER FRAME STATE RESTORE FRAME UNWIND ON FRAME UNWIND OFF FUNCTION or PROC GBLA, GBLL, and GBLS GET or INCLUDE IF, ELSE, ENDIF, and ELIF IMPORT and EXTERN INCBIN INFO KEEP LCLA, LCLL, and LCLS LTORG MACRO and MEND MAP MEXIT NOFP OPT QN, DN, and SN RELOC REQUIRE REQUIRE8 and PRESERVE8 RLIST RN ROUT SETA, SETL, and SETS SPACE or FILL THUMB directive TTL and SUBT WHILE and WEND WN and XN armasm-Specific A32 and T32 Instruction Set Featur armasm support for the CSDB instruction A32 and T32 pseudo-instruction summary ADRL pseudo-instruction CPY pseudo-instruction LDR pseudo-instruction MOV32 pseudo-instruction NEG pseudo-instruction UND pseudo-instruction Appendixes

IF, ELSE, ENDIF, and ELIF

F6.45 IF, ELSE, ENDIF, and ELIF

The IF, ELSE, ENDIF, and ELIF directives allow you to conditionally assemble sequences of instructions and directives.

Syntax

    IF logical-expression 
        …;code
    {ELSE
        …;code}
    ENDIF

where:

logical-expression

is an expression that evaluates to either {TRUE} or {FALSE}.

Usage

Use IF with ENDIF, and optionally with ELSE, for sequences of instructions or directives that are only to be assembled or acted on under a specified condition.

IF...ENDIF conditions can be nested.

The IF directive introduces a condition that controls whether to assemble a sequence of instructions and directives. [ is a synonym for IF.

The ELSE directive marks the beginning of a sequence of instructions or directives that you want to be assembled if the preceding condition fails. | is a synonym for ELSE.

The ENDIF directive marks the end of a sequence of instructions or directives that you want to be conditionally assembled. ] is a synonym for ENDIF.

The ELIF directive creates a structure equivalent to ELSE IF, without the requirement for nesting or repeating the condition.

Using ELIF

Without using ELIF, you can construct a nested set of conditional instructions like this:

    IF logical-expression
            instructions 
    ELSE
        IF logical-expression2
            instructions 
        ELSE
            IF logical-expression3
                instructions 
            ENDIF
        ENDIF
    ENDIF

A nested structure like this can be nested up to 256 levels deep.

You can write the same structure more simply using ELIF:

    IF logical-expression
        instructions 
    ELIF logical-expression2
        instructions 
    ELIF logical-expression3
        instructions 
    ENDIF

This structure only adds one to the current nesting depth, for the IF...ENDIF pair.

Examples

The following example assembles the first set of instructions if NEWVERSION is defined, or the alternative set otherwise:

Assembly conditional on a variable being defined
        IF :DEF:NEWVERSION
            ; first set of instructions or directives
        ELSE
            ; alternative set of instructions or directives
        ENDIF

Invoking armasm as follows defines NEWVERSION, so the first set of instructions and directives are assembled:

armasm --cpu=8-A.32 --predefine "NEWVERSION SETL {TRUE}" test.s

Invoking armasm as follows leaves NEWVERSION undefined, so the second set of instructions and directives are assembled:

armasm --cpu=8-A.32 test.s

The following example assembles the first set of instructions if NEWVERSION has the value {TRUE}, or the alternative set otherwise:

Assembly conditional on a variable value
        IF NEWVERSION = {TRUE}
            ; first set of instructions or directives
        ELSE
            ; alternative set of instructions or directives
        ENDIF

Invoking armasm as follows causes the first set of instructions and directives to be assembled:

armasm --cpu=8-A.32 --predefine "NEWVERSION SETL {TRUE}" test.s

Invoking armasm as follows causes the second set of instructions and directives to be assembled:

armasm --cpu=8-A.32 --predefine "NEWVERSION SETL {FALSE}" test.s
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