4.7.49. Named register variables

The compiler enables you to access registers of an ARM architecture-based processor using named register variables. Named register variables are supported:

Syntax

register type var-name __asm(reg);

Where:

type

is the type of the named register variable.

Any type of the same size as the register being named can be used in the declaration of a named register variable. The type can be a structure, but note that bitfield layout is sensitive to endianness.

var-name

is the name of the named register variable.

reg

is a character string denoting the name of a register on an ARM architecture-based processor.

Registers available for use with named register variables on ARM architecture-based processors are shown in Table 4.16.

Table 4.16. Named registers available on ARM architecture-based processors

RegisterCharacter string for __asm
CPSR

"cpsr" or "apsr"

SPSR

"spsr"

r0 to r12"r0" to "r12"
r13 or sp"r13" or "sp"
r14 or lr"r14" or "lr"
r15 or pc"r15" or "pc".

On targets with a VFP, the registers of Table 4.17 are also available for use with named register variables.

Table 4.17. Named registers available on targets with a VFP

RegisterCharacter string for __asm
FPSID "fpsid"
FPSCR "fpscr"
FPEXC "fpexc"

Example

void foo(void)
{
    register int foo __asm("r0");
}

In this example, foo is declared as a named register variable for the register r0.

See also

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