Chapter 14.

CRIS Dependent Features

14.1. Command line Options

The CRIS version of

as

has these machine dependent command line options.

The format of the generated object files can be either ELF or a.out, specified by the command line

options

 emulation=crisaout

and

 emulation=criself

. The default is ELF (criself), unless

as

has been configured specifically for a.out by using the configuration name

cris axis aout

.

There are two different link incompatible ELF object file variants for CRIS, for use in environments

where symbols are expected to be prefixed by a leading

_

character and for environments without

such a symbol prefix. The variant used for GNU/Linux port has no symbol prefix. Which variant

to produce is specified by either of the options

 underscore

and

 no underscore

. The default

is

 underscore

. Since symbols in CRIS a.out objects are expected to have a

_

prefix, specifying

 no underscore

when generating a.out objects is an error. Besides the object format difference, the

effect of this option is to parse register names differently. The

 no underscore

option makes a

$

register prefix mandatory.

The option

 pic

must be passed to

as

in order to recognize the symbol syntax used for ELF (SVR4

PIC) position independent code. This will also affect expansion of instructions. The expansion with

 pic

will use PC relative rather than (slightly faster) absolute addresses in those expansions.

When

 N

is specified,

as

will emit a warning when a 16 bit branch instruction is expanded into a

32 bit multiple instruction construct (Section 14.2 Instruction expansion).

Some versions of the CRIS v10, for example in the Etrax 100 LX, contain a bug that causes destabiliz 

ing memory accesses when a multiply instruction is executed with certain values in the first operand

just before a cache miss. When the

 mul bug abort

command line option is active (the default

value),

as

will refuse to assemble a file containing a multiply instruction at a dangerous offset, one

that could be the last on a cache line, or is in a section with insufficient alignment. This placement

checking does not catch any case where the multiply instruction is dangerously placed because it is

located in a delay slot. The

 mul bug abort

command line option turns off the checking.

14.2. Instruction expansion

as

will silently choose an instruction that fits the operand size for

[register+constant]

operands.

For example, the offset

127

in

move.d [r3+127],r4

fits in an instruction using a signed byte offset.

Similarly,

move.d [r2+32767],r1

will generate an instruction using a 16 bit offset. For symbolic

expressions and constants that do not fit in 16 bits including the sign bit, a 32 bit offset is generated.

For branches,

as

will expand from a 16 bit branch instruction into a sequence of instructions that can

reach a full 32 bit address. Since this does not correspond to a single instruction, such expansions can

optionally be warned about. Section 14.1 Command line Options.

14.3. Syntax

There are different aspects of the CRIS assembly syntax.