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Compiler Reference Guide

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



The EXPORT directive declares a symbol that can be used by the linker to resolve symbol references in separate object and library files. GLOBAL is a synonym for EXPORT.



EXPORT symbol {[SIZE=n]}

EXPORT symbol {[type{,set}]}

EXPORT symbol [attr{,type{,set}}{,SIZE=n}]

EXPORT symbol [WEAK {,attr}{,type{,set}}{,SIZE=n}]



is the symbol name to export. The symbol name is case-sensitive. If symbol is omitted, all symbols are exported.


symbol is only imported into other sources if no other source exports an alternative symbol. If [WEAK] is used without symbol, all exported symbols are weak.


can be any one of:


sets the ELF symbol visibility to STV_DEFAULT.


sets the ELF symbol visibility to STV_PROTECTED.


sets the ELF symbol visibility to STV_HIDDEN.


sets the ELF symbol visibility to STV_INTERNAL.


specifies the symbol type:


symbol is treated as data when the source is assembled and linked.


symbol is treated as code when the source is assembled and linked.


symbol is treated as a particular ELF symbol, as specified by the value of n, where n can be any number from 0 to 15.

If unspecified, the assembler determines the most appropriate type. Usually the assembler determines the correct type so you are not required to specify it.


specifies the instruction set:


symbol is treated as an A32 symbol.


symbol is treated as a T32 symbol.

If unspecified, the assembler determines the most appropriate set.


specifies the size and can be any 32-bit value. If the SIZE attribute is not specified, the assembler calculates the size:

  • For PROC and FUNCTION symbols, the size is set to the size of the code until its ENDP or ENDFUNC.

  • For other symbols, the size is the size of instruction or data on the same source line. If there is no instruction or data, the size is zero.


Use EXPORT to give code in other files access to symbols in the current file.

Use the [WEAK] attribute to inform the linker that a different instance of symbol takes precedence over this one, if a different one is available from another source. You can use the [WEAK] attribute with any of the symbol visibility attributes.


        AREA    Example,CODE,READONLY
        EXPORT  DoAdd           ; Export the function name
                                ; to be used by external modules.
DoAdd   ADD     r0,r0,r1

Symbol visibility can be overridden for duplicate exports. In the following example, the last EXPORT takes precedence for both binding and visibility:

        EXPORT  SymA[WEAK]      ; Export as weak-hidden
        EXPORT  SymA[DYNAMIC]   ; SymA becomes non-weak dynamic.

The following examples show the use of the SIZE attribute:

        EXPORT symA [SIZE=4]
        EXPORT symA [DATA, SIZE=4]
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