[LLVMdev] Proposal: Adding aligned instruction bundle support to MC

[Greg Fitzgerald]

> But if you just want to see the code and the diff against upstream...

If others are interested as well, here's all your changes via Github's
"compare" feature:

https://github.com/garious/llvm/compare/master...chromium<https://mymail.qualcomm.com/owa/redir.aspx?C=yu3Jo4nVdU6kh1OLiSe-04bnBhWtps8IxTOCi0lWLdEE4UxDImiKxfAW68FhXG16blXtZLHc6Xs.&URL=https%3a%2f%2fgithub.com%2fgarious%2fllvm%2fcompare%2fmaster...chromium>

Fascinating stuff guys.  What a great contribution.

-Greg



On Tue, Dec 4, 2012 at 9:03 PM, Derek Schuff <dschuff at google.com> wrote:

> Hi Greg,
> Our repos are public already, hosted on the Chromium infrastructure.
> Our builds are based out of the Native Client repository. The nacl git
> mirror is at http://git.chromium.org/native_client/src/native_client.git
> (no gitweb, sorry). That repo has pointers to a bunch of other repos
> which make pnacl (LLVM, clang, binutils, and a few others. see the
> file pnacl/DEPS for more).
> But if you just want to see the code and the diff against upstream,
> our LLVM repo is in
>
> https://gerrit.chromium.org/gerrit/gitweb?p=native_client%2Fpnacl-llvm.git;a=shortlog;h=refs%2Fheads%2Fmaster
> All of our clang changes are upstream already.
>
> -Derek
>
> On Tue, Dec 4, 2012 at 5:23 PM, Greg Fitzgerald <garious at gmail.com> wrote:
> > Hi Eli,
> >
> >> we are splitting the effort to manageable chunks that can
> >> be committed, tested and reviewed separately as
> >> independently as feasible
> >
> > I'd be interested in experimenting with this stuff sooner than later.
>  Could
> > you dump all the patches in a publicly accessible repo?  How about
> Github?
> >
> > Thanks,
> > Greg
> >
> >
> >
> > On Tue, Dec 4, 2012 at 3:53 PM, Eli Bendersky <eliben at google.com> wrote:
> >>
> >> Hello,
> >>
> >> We (the Portable Native Client team) would like to start upstreaming
> >> our LLVM modifications which contain support for Software Fault
> >> Isolation (SFI) as required for sandboxing programs to run under
> >> Native Client. Since the "total patch size" is quite big, we are
> >> splitting the effort to manageable chunks that can be committed,
> >> tested and reviewed separately as independently as feasible.
> >>
> >> One of the first things we'd like to start with is support for aligned
> >> instruction bundles in MC (assembler) level. This support exists in
> >> gas since binutils version 2.23
> >>
> >> (
> http://sourceware.org/binutils/docs/as/Bundle-directives.html#Bundle-directives
> ).
> >> Succinctly, the initial proposal is to add the following directives:
> >>
> >> .bundle_align_mode <num>
> >> .bundle_lock
> >> .bundle_unlock
> >>
> >> With the following semantics:
> >>
> >> When aligned instruction bundle mode ("bundling" in short) is enabled
> >> (.bundle_align_mode was encountered with an argument > 0, which is the
> >> power of 2 to which the bundle size is equal), single
> >> instructions and groups of instructions between .bundle_lock and
> >> .bundle_unlock directives cannot cross a bundle boundary.
> >>
> >> For example, consider the following:
> >>
> >> .bundle_align_mode 4
> >> mov1
> >> mov2
> >> mov3
> >>
> >> Assuming that each of the mov instructions is 7 bytes long and mov1 is
> >> aligned to a 16-byte boundary, two bytes of NOP padding will be
> >> inserted between mov2 and mov3 to make sure that mov3 does not cross a
> >> 16-byte bundle boundary.
> >>
> >> A slightly modified example:
> >>
> >> .bundle_align_mode 4
> >> mov1
> >> .bundle_lock
> >> mov2
> >> mov3
> >> .bundle_unlock
> >>
> >> Here, since the bundle-locked sequence "mov2 mov3" cannot cross a
> >> bundle boundary, 9 bytes of NOP padding will be inserted between mov1
> >> and mov2.
> >>
> >> For information on how this ability is used for software fault
> >> isolation by Native Client, see the following resources:
> >>
> >> * http://src.chromium.org/viewvc/native_client/data/site/NaCl_SFI.pdf[PDF
> >> link]
> >> *
> >>
> http://www.chromium.org/nativeclient/reference/arm-overview#TOC-The-Native-Client-Solution:-Bundles-
> >> * Other papers listed at
> >> http://www.chromium.org/nativeclient/reference/research-papers
> >>
> >> We want to start with this feature because it is self-contained in MC,
> >> makes LLVM more compatible with gas, level and can be easily tested.
> >> Future upstreaming efforts will be able to build upon this
> >> functionality.
> >>
> >> Any comments, ideas and suggestions are welcome.
> >>
> >> Eli
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
> >
> >
> > _______________________________________________
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> >
>
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