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ARM Compiler Reference

Inline assembler

The ARM C++ compilers support the syntax in the ISO/IEC C++ standard, with the

restriction that the string-literal must be a single string, for example:

asm("instruction[;instruction]");

The

asm

declaration must be inside a C++ function. You cannot include comments in the

string literal.

The ARM C and C++ compilers also support an extended inline assembler syntax,

introduced by the

asm

keyword (C++), or the

__asm

keyword (C and C++).

The inline assembler is invoked with the assembler specifier, and is followed by a list

of assembler instructions inside braces, for example:

__asm

{

instruction [; instruction]

...

[instruction]

}

If two instructions are on the same line, you must separate them with a semicolon. If an

instruction requires more than one line, line continuation must be specified with the

backslash character

. You can use C or C++ comments anywhere within an inline

assembly language block.

You can use an

asm

__asm

statement anywhere a statement is expected.

The ARM compilers support the full ARM instruction set, including generic

coprocessor instructions, but not

and

BLX

The Thumb compilers support the full Thumb instruction set except for

and

BLX

Using inline Thumb assembly routines, however, is deprecated and generates a warning

message.

See the chapter on Mixing C, C++, and assembly language in the ADS Developer Guide

for more information on inline C and C++ assemblers.

Keywords

ARM implements some keyword extensions for functions and variables. See:

• Function keywords on page 3-6

• Variable declaration keywords on page 3-9

• Type qualifiers on page 3-12.

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