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ARM Assembler Directives

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Generally, the Microsoft ARM assembler uses the ARM assembly language, which is documented in the ARM Compiler armasm Reference 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 Compiler armasm Reference 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 doesn't allow. Use the THUMB directive instead, along with UAL syntax.

  • COMMON

    Specification of an alignment for the common region isn't supported.

  • DCDO

    Not supported.

  • DN, QN, SN

    Specification of a type or a lane on the register alias isn't supported.

  • ENTRY

    Not supported.

  • EQU

    Specification of a type for the defined symbol isn't supported.

  • EXPORT and GLOBAL

    Specifies exports using this syntax:

    EXPORT|GLOBAL symbol{[type]}

    symbol 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

    The assembly syntax lets you specify a custom calling convention on procedures: you list the registers that are caller-save, and the ones that are callee-save. However, while the Microsoft ARM assembler accepts the syntax, it ignores the register lists. The debug information that's produced by the assembler supports only the default calling convention.

  • IMPORT and EXTERN

    Specifies imports using this syntax:

    IMPORT|EXTERN symbol{, WEAK alias{, TYPE t}}

    symbol is the name of the symbol to be imported.

    If WEAK alias is specified, it indicates that symbol is a weak external. If a definition for it isn't 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 symbol. These values for t are possible:

    Value Description
    1 Don't search libraries for symbol.
    2 Search libraries for symbol.
    3 symbol is an alias for alias (default).

    EXTERN is a synonym for IMPORT, except that symbol 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 isn't supported. Default values for macro parameters aren't supported.

  • NOFP

    Not supported.

  • OPT, TTL, SUBT

    Not supported, because the Microsoft ARM assembler doesn't produce listings.

  • PRESERVE8

    Not supported.

  • RELOC

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

  • REQUIRE

    Not supported.

  • REQUIRE8

    Not supported.

  • THUMBX

    Not supported, because the Microsoft ARM assembler doesn't support the Thumb-2EE instruction set.

See also

ARM Assembler Command-Line Reference
ARM Assembler Diagnostic Messages