Re: SPARC gold / ld support

[Ian Lance Taylor <iant at google dot com>]

Jorge PÃrez <jernestop@gmail.com> writes:

> I'm looking forward to implement the SPARC V8 for an embedded
> application and since I have very limited memory resources, I'm
> interested in obtaining the best possible code density. I'm wondering
> if with these regards is there a remarkable difference between LD and
> GOLD?

The gold linker is intended to be faster than the GNU linker but is
otherwise more or less compatible for normal use.  That said, using a
linker script slows gold down a lot.


> Besides, given the hard constraints of my target, I do not need / care
> about the code being position independent (PIC). In fact, I
> intentionally located the .rodata section of my programs at 0x00000000
> so the high22 bits of the SETHI instructions pointing at .rodata are
> set to 0. This, in principle, would let me get rid of most SETHI
> instructions, or at least those pointing to the .rodata section for
> instance. As an example, I can reduce the code size of a Paranoia
> bench by 19% which is huge in the embedded context. However I do not
> know if such modification is feasible / possible / already implemented
> at the linker level (ld, gold?).

The linkers are not going to be able to remove sethi instructions for
you.  For that you need to get the compiler to not generate them in
the first place.  I'm not aware of any compiler option to disable
generating sethi instructions.

It would be theoretically possible to remove sethi instructions in
either linker as a relaxation, but it would require a decent amount of
code analysis, or it would require compiler support.  None of this
exists as far as I know.

Ian