[Bug gas/11102] New: AVR gs() operator cant be used in simple expressions

[hutchinsonandy at gcc dot gnu dot org]

AVR target uses the GAS gs() operator'
On smaller devices  it simply provides a word address.
On large devices >64K words such as -mmcu=avr6 it creates trampoline jump table
entry and return its location. This allows 16bit addressing to access 24bit
space of large memory devices.


However, the gs() cannot be used within another operator - for example

        ldi r24,lo8(2+gs(test_func))

will give:

test.s:44: Error: `)' required
test.s:44: Error: garbage at end of line

This currently (4.5 head) prevent avr-gcc using any simple pointer arithmetic.

Depening on code and optimization, gcc may create constant or evaluated
expression for pointers manipulations such as

 void (* x) (void);
 x = test_func;
 x= x + 2;

which may be optimized into

x = (test_func+2);


which can be passed to gas as gs(test_func+2) or gs(test_func) with +2 done by
assembler instructions

However, there are two problems:

First is that gs() returns word address - thus it should be gs(test_func+4).  I
can hack avr-gcc backend to take care of this and then at least pointer
arithmetic work for smaller devices.

The second unsolvable problem applies to large devices -mmcu=avr6 where
trampolines are created by gs().

The above example will create trampoline entries to jump to(test_func+2) or
(test_func) depending on optimization level. What we really need is to always
create trampoline entry for test_func and then add 2. eg

ldi r24,lo8(2+gs(test_func))

avr-gcc can be modified to create this format - unfortunately gas wont take it -
preventing any pointer arithmetic from being used on avr6 device type.

-- 
           Summary: AVR gs()  operator cant be used in simple expressions
           Product: binutils
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gas
        AssignedTo: unassigned at sources dot redhat dot com
        ReportedBy: hutchinsonandy at gcc dot gnu dot org
                CC: bug-binutils at gnu dot org
GCC target triplet: avr-*-*


http://sourceware.org/bugzilla/show_bug.cgi?id=11102

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