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ARM Assembler Directives

For the most part, the Microsoft ARM assembler uses the ARM assembly language, which is documented in Chapter 7 of the ARM assembler tools guide. However, the Microsoft implementations of some assembly directives differ from the ARM assembly directives. This article explains the differences.

Microsoft Implementations of ARM Assembly Directives

  • AREA
    The Microsoft ARM assembler supports these AREA attributes: ALIGN, CODE, CODEALIGN, DATA, NOINIT, READONLY, READWRITE, THUMB, ARM.

    All except THUMB and ARM work as documented in the ARM assembler tools guide.

    In the Microsoft ARM assembler, THUMB indicates that a CODE section contains Thumb code, and is the default for CODE sections. ARM indicates that the section contains ARM code.

  • ATTR
    Not supported.

  • CODE16
    Not supported because it implies pre-UAL Thumb syntax, which the Microsoft ARM assembler does not allow. Use the THUMB directive instead, along with UAL syntax.

  • COMMON
    Specification of an alignment for the common region is not supported.

  • DCDO
    Not supported.

  • DN, QN, SN
    Specification of a type or a lane on the register alias is not supported.

  • ENTRY
    Not supported.

  • EQU
    Specification of a type for the defined symbol is not supported.

  • EXPORT and GLOBAL
    EXPORTsym {[type]}

    sym is the symbol to be exported. [type], if specified, can be either [DATA] to indicate that the symbol points to data or [FUNC] to indicate that the symbol points to code.

    GLOBAL is a synonym for EXPORT.

  • EXPORTAS
    Not supported.

  • FRAME
    Not supported.

  • FUNCTION and PROC
    Although the assembly syntax supports the specification of a custom calling convention on procedures by listing the registers that are caller-save and those that are callee-save, the Microsoft ARM assembler accepts the syntax but ignores the register lists. The debug information that is produced by the assembler supports only the default calling convention.

  • IMPORT and EXTERN
    IMPORT sym{, WEAK alias{, TYPE t}}

    sym is the name of the symbol to be imported.

    If WEAK alias is specified, it indicates that sym is a weak external. If no definition for it is found at link time, then all references to it bind instead to alias.

    If TYPE t is specified, then t indicates how the linker should attempt to resolve sym. These values for t are possible:
    1—Do not perform a library search for sym
    2—Perform a library search for sym
    3—sym is an alias for alias (default)

    EXTERN is a synonym for IMPORT, except that sym is imported only if there are references to it in the current assembly.

  • MACRO
    The use of a variable to hold the condition code of a macro is not supported. Default values for macro parameters are not supported.

  • NOFP
    Not supported.

  • OPT, TTL, SUBT
    Not supported because the Microsoft ARM assembler does not produce listings.

  • PRESERVE8
    Not supported.

  • RELOC
    RELOC n can only follow an instruction or a data definition directive. There is no "anonymous symbol" that can be relocated.

  • REQUIRE
    Not supported.

  • REQUIRE8
    Not supported.

  • THUMBX
    Not supported because the Microsoft ARM assembler does not support the Thumb-2EE instruction set.

See Also

Reference

ARM Assembler Command-Line Reference

ARM Assembler Diagnostic Messages