On 02/17/2012 11:34 AM, Peter Bigot wrote:
> A couple lines are commented out because the current assembler won't
> process them, something I consider to be a bug. I would be interested in
> knowing if other tools accept $ as denoting the program location counter in
> contexts other than jump instructions, and if so whether it means the
> beginning of the instruction or the address of the offset encoded internal
> to the instruction.
I usually use . for the current location.
jmp .
jmp .+0
jmp .+2
jmp .+0x100
produces:
44: ff 3f jmp $+0 ;abs 0x44
46: ff 3f jmp $+0 ;abs 0x46
48: 00 3c jmp $+2 ;abs 0x4a
4a: 7f 3c jmp $+256 ;abs 0x14a
Looking at the documentation (info gas) in machine dependencies it says:
The character `$' in jump instructions indicates current location and
implemented only for TI syntax compatibility.
So I would say that using $ in the mov instructions shouldn't be
expected to work but that the implementation for using $ in jumps is
messed up.
Digging into the source (not the appropriate version but what I recently
grabbed while playing with things ARM Cortex-M4, aka 2.22.51) it looks
like this is in tc-msp430.c. At least I find the error message
"instruction requires label sans '$'" there.
But I have never dug down into the internals of gas so things get murky
after this. I do see a fixup of the offset that specifically excludes zero.
if ((*l1 == '$' && x > 0) || x < 0)
x -= 2;
--
David W. Schultz
http://home.earthlink.net/~david.schultz
"Who? What? Where? When? Aahhhg!" - Duck Dodgers
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