Subzero, MIPS32: Randomly insert NOP

Subzero, MIPS32: Randomly insert NOP

Patch implements randomlyInsertNop for MIPS32. Separate test case
added because current test is based on function with vector
operands, which MIPS32 does not support yet.
run-pnacl-sz.py updated, to pass -z argument to objdump, so it does
not hide multiple nops (shows ... instead) between instruction.

R=stichnot@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=8fbddc6b522683a2d238edee6c07b05e3c718983

[obucinac, 2016-09-14 16:03:09]

Description was changed from

==========
Subzero, MIPS32: Randomly insert NOP

Patch implements randomlyInsertNop for MIPS32. Separate test case
added because current test is based on function with vector
operands, which MIPS32 does not support yet.
run-pnacl-sz.py updated, to pass -z argument to objdump, so it does
not hide multiple nops (shows ... instead) between instruction.
==========

to

==========
Subzero, MIPS32: Randomly insert NOP

Patch implements randomlyInsertNop for MIPS32. Separate test case
added because current test is based on function with vector
operands, which MIPS32 does not support yet.
run-pnacl-sz.py updated, to pass -z argument to objdump, so it does
not hide multiple nops (shows ... instead) between instruction.
==========

[obucinac, 2016-09-14 16:03:09]

obucinac@gmail.com changed reviewers:
+ eholk@chromium.org, jaydeep.patil@imgtec.com, jpp@chromium.org,
kschimpf@google.com, sagar.thakur@imgtec.com, stichnot@chromium.org

[obucinac, 2016-09-14 16:06:16]

One comment here...

By MIPS instruction reference, available from the link below, page 293, NOP
instruction is interpreted in hardware as sll $zero, $zero, 0. This is why I
implemented it the way I did. Test case output code is dissasembled, in order to
show proper conversion from sll, $zero, $zero, 0 to nop.

https://imagination-technologies-cloudfront-assets.s3.amazonaws.com/documenta...

[Jim Stichnoth, 2016-09-15 05:24:20]

Note: I would personally put low priority on implementing these various code
diversity/randomization techniques, because as it turns out they are never
actually used in production.

https://codereview.chromium.org/2340733003/diff/1/pydir/run-pnacl-sz.py
File pydir/run-pnacl-sz.py (right):

https://codereview.chromium.org/2340733003/diff/1/pydir/run-pnacl-sz.py#newco...
pydir/run-pnacl-sz.py:205: # Show wide instruction encodings, diassemble, and
show relocs.
Update the comment for '-z' ?

[obucinac, 2016-09-15 10:44:56]

https://codereview.chromium.org/2340733003/diff/1/pydir/run-pnacl-sz.py
File pydir/run-pnacl-sz.py (right):

https://codereview.chromium.org/2340733003/diff/1/pydir/run-pnacl-sz.py#newco...
pydir/run-pnacl-sz.py:205: # Show wide instruction encodings, diassemble, and
show relocs.
On 2016/09/15 05:24:20, stichnot wrote:
> Update the comment for '-z' ?

Done.

[obucinac, 2016-09-15 10:46:57]

On 2016/09/15 05:24:20, stichnot wrote:
> Note: I would personally put low priority on implementing these various code
> diversity/randomization techniques, because as it turns out they are never
> actually used in production.

No problem. These tasks are not in our focus, but this one was really easy and
relaxing :)
And we may need nop at other places (usually branches with delay slots).

[Jim Stichnoth, 2016-09-16 00:26:30]

lgtm

https://codereview.chromium.org/2340733003/diff/20001/tests_lit/llvm2ice_test...
File tests_lit/llvm2ice_tests/nop-insertion-no-vectors.ll (right):

https://codereview.chromium.org/2340733003/diff/20001/tests_lit/llvm2ice_test...
tests_lit/llvm2ice_tests/nop-insertion-no-vectors.ll:1: ; RUN: %p2i -i %s
--filetype=asm --assemble --disassemble --target=mips32 \
"make -f Makefile.standalone presubmit" fails early because the MINIMAL build
doesn't support filetype=asm.

I went ahead and added the "REQUIRES: allow_dump" incantation.

[Jim Stichnoth, 2016-09-16 00:26:43]

Description was changed from

==========
Subzero, MIPS32: Randomly insert NOP

Patch implements randomlyInsertNop for MIPS32. Separate test case
added because current test is based on function with vector
operands, which MIPS32 does not support yet.
run-pnacl-sz.py updated, to pass -z argument to objdump, so it does
not hide multiple nops (shows ... instead) between instruction.
==========

to

==========
Subzero, MIPS32: Randomly insert NOP

Patch implements randomlyInsertNop for MIPS32. Separate test case
added because current test is based on function with vector
operands, which MIPS32 does not support yet.
run-pnacl-sz.py updated, to pass -z argument to objdump, so it does
not hide multiple nops (shows ... instead) between instruction.

R=stichnot@chromium.org

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

[Jim Stichnoth, 2016-09-16 00:26:44]

Committed patchset #2 (id:20001) manually as
8fbddc6b522683a2d238edee6c07b05e3c718983 (presubmit successful).