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Chapter 14. CRIS Dependent Features

14.3.1. Special Characters

The character

#

is a line comment character. It starts a comment if and only if it is placed at the

beginning of a line.

A

;

character starts a comment anywhere on the line, causing all characters up to the end of the line

to be ignored.

A

@

character is handled as a line separator equivalent to a logical new line character (except in a

comment), so separate instructions can be specified on a single line.

14.3.2. Symbols in position independent code

When generating position independent code (SVR4 PIC) for use in cris axis linux gnu shared li 

braries, symbol suffixes are used to specify what kind of run time symbol lookup will be used, ex 

pressed in the object as different relocation types. Usually, all absolute symbol values must be located

in a table, the global offset table, leaving the code position independent; independent of values of

global symbols and independent of the address of the code. The suffix modifies the value of the sym 

bol, into for example an index into the global offset table where the real symbol value is entered, or

a PC relative value, or a value relative to the start of the global offset table. All symbol suffixes start

with the character

:

(omitted in the list below). Every symbol use in code or a read only section must

therefore have a PIC suffix to enable a useful shared library to be created. Usually, these constructs

must not be used with an additive constant offset as is usually allowed, i.e. no 4 as in

symbol + 4

is

allowed. This restriction is checked at link time, not at assembly time.

GOT

Attaching this suffix to a symbol in an instruction causes the symbol to be entered into

the global offset table. The value is a 32 bit index for that symbol into the global offset

table. The name of the corresponding relocation is

R_CRIS_32_GOT

. Example:

move.d

[$r0+extsym:GOT],$r9

GOT16

Same as for

GOT

, but the value is a 16 bit index into the global offset table. The corresponding

relocation is

R_CRIS_16_GOT

. Example:

move.d [$r0+asymbol:GOT16],$r10

PLT

This suffix is used for function symbols. It causes a procedure linkage table, an array of code

stubs, to be created at the time the shared object is created or linked against, together with a

global offset table entry. The value is a pc relative offset to the corresponding stub code in the

procedure linkage table. This arrangement causes the run time symbol resolver to be called to

look up and set the value of the symbol the first time the function is called (at latest; depending

environment variables). It is only safe to leave the symbol unresolved this way if all references

are function calls. The name of the relocation is

R_CRIS_32_PLT_PCREL

. Example:

add.d

fnname:PLT,$pc

PLTG

Like PLT, but the value is relative to the beginning of the global offset table. The relocation is

R_CRIS_32_PLT_GOTREL

. Example:

move.d fnname:PLTG,$r3

GOTPLT

Similar to

PLT

, but the value of the symbol is a 32 bit index into the global offset table. This

is somewhat of a mix between the effect of the

GOT

and the

PLT

suffix; the difference to

GOT

is that there will be a procedure linkage table entry created, and that the symbol is assumed to