Re: [Qemu-devel] [PATCH 0/6] relicense QEMU softfloat from 2b to to 2a

[Peter Maydell]

Hi; this is a ping (with some of the less frequent contributors
taken off cc), because I'd really like it if we could get this
issue dealt with (preferably before a flood of new patches to
softfloat arrive after the tree reopens for 2.3), but this patchset
needs review (for methodology, of my reimplemented functions, and
of whether we should avoid the bisection break).

thanks
-- PMM

On 25 November 2014 at 14:17, Peter Maydell <address@hidden> wrote:
> [If you're not a regular QEMU contributor: you are CC'd on this
> just for your information and because you provided an Acked-by for
> the previous version of this patch back in 2013; thanks! No action
> is required from you. Regular contributors are invited to review
> the patchset.]
>
> Hi; as you may be aware, we discovered some time back that
> the license of SoftFloat-2b is claimed to be GPLv2 incompatible by
> the FSF due to an indemnification clause.  The previous release,
> SoftFloat-2a, did not contain this clause. We're therefore switching
> to the -2a release and relicensing (or reverting and reimplementing)
> all subsequent commits by QEMU contributors.
>
> Last time around we were able to collect acks for the relicensing
> from almost all contributors, so thanks to all of you. This patchset
> aims to complete the process by applying the relicensing patch and
> providing reimplemented code for the handful of commits that had to
> be reverted.
>
> The patch switching from upstream's SoftFloat-2b to -2a is
> constructed in the same way Anthony Liguori used in 2013:
>  * diff commit 158142c2 against SoftFloat-2b to separate out the
>    changes made by Fabrice as part of the import
>  * copy over the SoftFloat-2a versions of the files instead
>  * apply some mechanical transformations (line endings, block comment style)
>  * re-apply Fabrice's patches
>  * diff this endpoint against 158142c2 to give a 2b-to-2a relicensing patch
>  * apply that to current master
>
> Conceptually I would have preferred to replay all of our QEMU
> commits after 158142c2 on top of the SoftFloat-2a equivalent
> (giving a sort of alternate-history master rebased on 2a) and then
> diffed that against the real-world master. However git cherry-pick
> chokes on merge commits. If anybody has better git skills than me
> and thinks this can be done then I'd be interested to see it.
> In any case the patch is I think equivalent -- it's just a matter of
> which two sides of a square you go round to reach the far corner.
>
> Following this change are a set of patches which revert the only four
> commits in the tree which are still relevant and for which we could not
> get acks for relicensing. I present them in this series as separate
> "revert" and "reimplement" patches, since this more clearly shows the
> intent. Obviously this will break bisection...
>
> Finally there's a patch which adds comments to the top of each
> affected file clarifying the new licensing status (where the files
> contain portions under variously SoftFloat-2a, BSD and GPLv2+
> licenses) and specifying the default license for new contributions (so
> we don't have to keep asking patch submitters to specify it). I've
> applied the Acked-by tags from the 2013 round to this patch as it
> seemed the most appropriate place. (Those acks should thus be taken to
> indicate approval for the relicensing rather than necessarily
> specifically for the wording choice.)
>
> Questions for review:
>  * can we do the git cherry-pick thing I mention above?
>  * should we squash the revert and reimplement patches together?
>    (avoids bisection break but makes the revert-and-reimplement less clear)
>  * would anybody like to cross-check my examination of the commit logs
>    to confirm I didn't miss any patches we need to revert?
>  * are there any bugs in my reimplementations?
>  * are people happy with my attempt to clarify the licensing status of
>    the source files in patch 6, and my choice of GPLv2+ for future
>    contributions to them?
>
> I've put the full details of how I constructed this patchset after the
> diffstat. References in that text to "this archive" are to
> http://people.linaro.org/~peter.maydell/softfloat-relicensing-proposed.tar.gz
> which is a complete archive of everything needed to reproduce the
> patchset, including copies of upstream's pristine 2a and 2b tarballs.
> If/when this patchset is applied I plan to upload it to the QEMU webserver
> as a permanent archive of what happened here (since the commit diffs
> themselves don't tell the full story).
>
> thanks
> -- PMM
>
> Peter Maydell (6):
>   softfloat: Apply patch corresponding to rebasing to softfloat-2a
>   softfloat: Revert remaining portions of commits 75d62a5856 and
>     3430b0be36f
>   softfloat: Revert remaining parts of commits b645bb4885 and 5a6932d51d
>   softfloat: Implement uint64_to_float64() and uint64_to_float32()
>   softfloat: reimplement SNAN_BIT_IS_ONE support
>   softfloat: Clarify license status
>
>  fpu/softfloat-macros.h     |  86 +++++++++++++++++++++-------
>  fpu/softfloat-specialize.h | 139 
> ++++++++++++++++++++++++++++++---------------
>  fpu/softfloat.c            | 136 +++++++++++++++++++++++++++++++-------------
>  include/fpu/softfloat.h    |  82 +++++++++++++++++++-------
>  4 files changed, 316 insertions(+), 127 deletions(-)
>
> --
> 1.9.1
>
> QEMU relicensing from SoftFloat-2b to SoftFloat-2a
> ==================================================
>
> This archive contains binaries, patches and documentation regarding the
> process of relicensing QEMU's softfloat code from 2b to 2a.
>
> The process followed is in two parts: replace the upstream
> SoftFloat code with the equivalent files from the upstream 2a release;
> and then revert and rewrite some later commits by QEMU contributors who
> could not be contacted to agree to a relicensing of their work.
>
> Replacement of upstream code
> ----------------------------
>
> This archive includes SoftFloat-2a.zip and SoftFloat-2b.zip, which
> are the original upstream source releases downloaded from:
>
> http://web.archive.org/web/19991004171915/http://http.cs.berkeley.edu/%7Ejhauser/arithmetic/SoftFloat-2a.zip
> http://www.jhauser.us/arithmetic/SoftFloat-2b.zip
>
> The differences between the two are minimal, consisting mostly of
> the license change and a change in the style used for block comments.
>
> Starting from the commit immediately before the original softfloat import
> (4f716dc681d1b) we can construct a series of commits which import the
> version 2a sources instead.
>
> First separate out the changes Fabrice wrote as part of the initial
> import from the upstream 2b changes, and save the patch for later:
>
>     cp SoftFloat-2b/softfloat/bits64/softfloat.c 2b-rearranged/fpu
>     cp SoftFloat-2b/softfloat/bits64/386-Win32-GCC/softfloat.h 
> 2b-rearranged/fpu/
>     cp SoftFloat-2b/softfloat/bits64/softfloat-macros 
> 2b-rearranged/fpu/softfloat-macros.h
>     cp SoftFloat-2b/softfloat/bits64/386-Win32-GCC/softfloat-specialize 
> 2b-rearranged/fpu/
> softfloat-specialize.h
>     dos2unix 2b-rearranged/fpu/*.[ch]
>     cd qemu
>     git checkout 158142c2c2df728cfa3b5320c65534921a764f26
>     cd ..
>     diff -uN 2b-rearranged/fpu qemu/fpu > fabrice-initial-changes.patch
>
> Now we can create the patchseries which is the equivalent 2a import:
>
>     cd qemu
>     git checkout 4f716dc681d1b
>
> Copy the 2a files and fix their line endings to Unix style:
>
>     cp ../SoftFloat-2a/softfloat/bits64/softfloat.c fpu
>     cp ../SoftFloat-2a/softfloat/bits64/386-Win32-gcc/softfloat.h fpu
>     cp ../SoftFloat-2a/softfloat/bits64/softfloat-macros 
> fpu/softfloat-macros.h
>     cp ../SoftFloat-2a/softfloat/bits64/386-Win32-gcc/softfloat-specialize 
> fpu/softfloat-specialize.h
>     dos2unix fpu/*.[ch]
>
> Add the new files and configure/makefile changes from 158142c2c2df
>
>     git checkout 158142c2c2df7 fpu/softfloat-native.c fpu/softfloat-native.h
>     git show 158142c2c2df7 Makefile.target configure | patch -p1
>
> Mechanically update comment style (the perl script used is provided in this 
> archive)
>
>     for f in fpu/softfloat-specialize.h fpu/softfloat-macros.h 
> fpu/softfloat.c fpu/softfloat.h; do fix-softfloat-comments $f > $f.new && mv 
> $f.new $f; done
>
> Delete a handful of blank lines to avoid spurious patch rejects.
>
> Apply the "Fabrice initial changes" patch created earlier:
> This requires a bunch of fuzzing but it does not fail on any hunks.
>
>      patch -N -p1 --fuzz 5 -i ../fabrice-initial-changes.patch
>
> The five commits that result from this process are archived in
> the reimport/ subdirectory.
>
> We can now create a patch by diffing the endpoint of this set of commits
> against the original upstream import commit 158142c2c2df7:
>      diff -u 158142c2c2df import-sf-2a > ../relicense-patch.txt
>
> That patch is also included in this archive. It consists entirely
> of changes to version numbers, licence text and a trivial comment
> reformat (as expected, since the upstream 2a to 2b changes were just this).
>
> We can then apply that patch to current QEMU master:
>      patch  -p1 --fuzz 10 <../relicense-patch.txt
> to produce a modern QEMU effectively rebased on version 2a of upstream
> SoftFloat.
>
> Reverting and rewriting of later QEMU commits
> ---------------------------------------------
>
> Since contributions to these softfloat files in QEMU after their
> initial import have to be assumed to have been provided by their
> authors under the SoftFloat-2b license, we needed to get permission
> from those authors to relicense their contributions under either
> the SoftFloat-2a license or some other GPLv2 compatible license.
> Most of these were collected in an email thread on qemu-devel
> in 2013 where we requested permission for relicensing changes which
> had been made up to that point. For all changes to these files after
> that date we confirmed with the patch submitter that they were willing
> to dual-license their change before applying the commit.
>
> The affected commits can be listed with:
>   git log -- fpu/softfloat.h fpu/softfloat.c fpu/softfloat-specialize.h 
> fpu/softfloat-macros.h include/fpu/softfloat.h
>
> The file fpu-logs.txt lists these commits, annotated to either
> to indicate that it's ok for relicensing, or to indicate that the
> commit must be reverted. Only four commits need reversion:
>  5a6932d51d1b, b645bb4885, 3430b0be36fb7 and 75d62a585629c
>
> The interesting cases (both the SFNOs and a handful of SFOK that
> were not trivially obviously OK) have been copied into 'sfno.txt'
> (to save you having to wade through the long list).
>
> Copies of all the emails where people provided Acks are in the ackmails/
> directory.
>
> The patches in the reverts/ directory:
>  * apply the relicense-patch
>  * revert those parts of commits 5a6932d51d1b, b645bb4885, 3430b0be36fb7 and
>    75d62a585629c which change the softfloat files and are still in the
>    QEMU tree
>  * independently reimplement the two functions and one bit of minor
>    functionality which those commits provided
>  * update the source files to indicate the now complicated licensing
>    that applies since some relicensing was to BSD or GPLv2+ rather than
>    softfloat-2a
>
> ---end of README---