ARM Assembler Directives

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