Subzero: Support non-IRT immediate calls with -filetype=iasm.

Subzero: Support non-IRT immediate calls with -filetype=iasm.

This is done by emitting the following:
  .byte 0xe8
  .long __Sz_AbsoluteZero -4 - .

The linker is passed an argument like
  --defsym=__Sz_AbsoluteZero=0
to force the symbol's value to 0.

This special symbol is needed due to an llvm-mc parsing bug.

BUG= none
R=jvoung@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=927f7ccc6beac42ae894c43cbc75b82919052cb5

[Jim Stichnoth, 2015-03-20 03:16:35]

stichnot@chromium.org changed reviewers:
+ jvoung@chromium.org

[jvoung (off chromium), 2015-03-20 06:10:45]

lgtm

https://codereview.chromium.org/1027593002/diff/1/pydir/crosstest.py
File pydir/crosstest.py (right):

https://codereview.chromium.org/1027593002/diff/1/pydir/crosstest.py#newcode150
pydir/crosstest.py:150: '-Wn,-defsym=__Sz_AbsoluteZero=0']
Subzero AbsoluteZero would be -0.0 ?

=)

https://codereview.chromium.org/1027593002/diff/1/pydir/szbuild.py
File pydir/szbuild.py (right):

https://codereview.chromium.org/1027593002/diff/1/pydir/szbuild.py#newcode300
pydir/szbuild.py:300: '--defsym __Sz_AbsoluteZero=0 ' +
Keep the same number of = as the other cases, like "--defsym=_...=0" for
consistency?

[Jim Stichnoth, 2015-03-20 06:22:53]

https://codereview.chromium.org/1027593002/diff/1/pydir/szbuild.py
File pydir/szbuild.py (right):

https://codereview.chromium.org/1027593002/diff/1/pydir/szbuild.py#newcode300
pydir/szbuild.py:300: '--defsym __Sz_AbsoluteZero=0 ' +
On 2015/03/20 06:10:45, jvoung wrote:
> Keep the same number of = as the other cases, like "--defsym=_...=0" for
> consistency?

Done.

There's now just one inconsistency - crosstest.py with sandboxing has to use
-defsym= instead of --defsym= .  I guess that could be fixed in pnacl-ld.py, but
it's not really a big deal...

[Jim Stichnoth, 2015-03-20 06:23:12]

Committed patchset #2 (id:20001) manually as
927f7ccc6beac42ae894c43cbc75b82919052cb5 (presubmit successful).