ARM Assembler Directives

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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

ARM Assembler Command-Line Reference
ARM Assembler Diagnostic Messages