git broken for AIX somewhere between 2.13.2 and 2.13.3

git broken for AIX somewhere between 2.13.2 and 2.13.3

[Michael]

Hi,

Several years ago I had downloaded and packaged git-2.10.1 with no real 
issues, and it has been working fine. Deciding it was time for an update 
I downloaded git-2.18.0 and built from scratch.

After testing lots of version - the the last 2.12 version worked; 
git-2.13.2 works but git-2.13.3 does not.

root@x066:[/tmp/xxx]git clone git@github.com:aixtools/hello-world.git
root@x066:[/tmp/xxx]git --version
git version 2.13.2
root@x066:[/tmp/xxx]ls -l
total 0
drwxr-xr-x    3 root     system          256 Jul 29 16:37 hello-world

root@x066:[/tmp/xxx]git --version
git version 2.13.3
root@x066:[/tmp/xxx]git clone git@github.com:aixtools/hello-world.git
Cloning into 'hello-world'...
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 3
Receiving objects: 100% (3/3), done.
fatal: pack is corrupted (SHA1 mismatch)
fatal: index-pack failed

p.s. - what surprises me re: git-2.13.2 - no messages about 'Cloning 
into ...', which version 2.13.1 did give.

I guess a bisect is the next step - between version 2.13.2 and 2.13.3. 
Other suggestions welcome!

Michael

Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[brian m. carlson]

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On Sun, Jul 29, 2018 at 06:44:26PM +0200, Michael wrote:
> root@x066:[/tmp/xxx]git --version
> git version 2.13.3
> root@x066:[/tmp/xxx]git clone git@github.com:aixtools/hello-world.git
> Cloning into 'hello-world'...
> remote: Counting objects: 3, done.
> remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 3
> Receiving objects: 100% (3/3), done.
> fatal: pack is corrupted (SHA1 mismatch)
> fatal: index-pack failed
> 
> p.s. - what surprises me re: git-2.13.2 - no messages about 'Cloning into
> ...', which version 2.13.1 did give.
> 
> I guess a bisect is the next step - between version 2.13.2 and 2.13.3. Other
> suggestions welcome!

Are you using SHA1DC on that system, and does compiling with another
SHA-1 implementation help?  There was a change to the SHA1DC code big
endian detection in that commit, which might be the cause of your
problems if you're using a POWER or PowerPC system.
-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204

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Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[Michael]

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On 29/07/2018 20:10, brian m. carlson wrote:
> On Sun, Jul 29, 2018 at 06:44:26PM +0200, Michael wrote:
>> root@x066:[/tmp/xxx]git --version
>> git version 2.13.3
>> root@x066:[/tmp/xxx]git clone git@github.com:aixtools/hello-world.git
>> Cloning into 'hello-world'...
>> remote: Counting objects: 3, done.
>> remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 3
>> Receiving objects: 100% (3/3), done.
>> fatal: pack is corrupted (SHA1 mismatch)
>> fatal: index-pack failed
>>
>> p.s. - what surprises me re: git-2.13.2 - no messages about 'Cloning into
>> ...', which version 2.13.1 did give.
>>
>> I guess a bisect is the next step - between version 2.13.2 and 2.13.3. Other
>> suggestions welcome!
> Are you using SHA1DC on that system, and does compiling with another
> SHA-1 implementation help?  There was a change to the SHA1DC code big
> endian detection in that commit, which might be the cause of your
> problems if you're using a POWER or PowerPC system.

I was thinking it might be an 'endian' issue. So, yes - AIX runs on 
POWER, only as BigEndian.

git bisect returns:

michael@x071:[/data/prj/aixtools/git/github/git-master]git bisect bad
Bisecting: 1 revision left to test after this (roughly 1 step)
[35049a2343948f686861e176a8c395f9f67da7b6] Merge branch 
'aw/contrib-subtree-doc-asciidoctor' into maint
michael@x071:[/data/prj/aixtools/git/github/git-master]git bisect good
Bisecting: 0 revisions left to test after this (roughly 0 steps)
[9936c1b52a39fa14fca04f937df3e75f7498ac66] sha1dc: update from upstream


michael@x071:[/data/prj/aixtools/git/github/git-master]git bisect bad
9936c1b52a39fa14fca04f937df3e75f7498ac66 is the first bad commit
commit 9936c1b52a39fa14fca04f937df3e75f7498ac66
Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date:   Sat Jul 1 22:05:45 2017 +0000

     sha1dc: update from upstream

     Update sha1dc from the latest version by the upstream maintainer[1].

     See commit 6b851e536b ("sha1dc: update from upstream", 2017-06-06) for
     the last update.

     This solves the Big Endian detection on Solaris reported against
     v2.13.2[2], hopefully without any regressions. A version of this has
     been tested on two Solaris SPARC installations, Cygwin (by jturney on
     cygwin@Freenode), and on numerous more boring systems (mainly
     linux/x86_64). See [3] for a discussion of the implementation and
     platform-specific issues.

     See commit a0103914c2 ("sha1dc: update from upstream", 2017-05-20) and
     6b851e536b ("sha1dc: update from upstream", 2017-06-06) for previous
     attempts in the 2.13 series to address various compile-time feature
     detection in this library.

     1. 
https://github.com/cr-marcstevens/sha1collisiondetection/commit/19d97bf5af05312267c2e874ee6bcf584d9e9681 

     2. 
<CAKKM46tHq13XiW5C8sux3=PZ1VHSu_npG8ExfWwcPD7rkZkyRQ@mail.gmail.com>
(https://public-inbox.org/git/CAKKM46tHq13XiW5C8sux3=PZ1VHSu_npG8ExfWwcPD7rkZkyRQ@mail.gmail.com/) 

     3. https://github.com/cr-marcstevens/sha1collisiondetection/pull/34

     Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     Signed-off-by: Junio C Hamano <gitster@pobox.com>

:040000 040000 a84797967fb742e4ca9618a641d53ce3a6c6589b 
32efa656d78901da961e4a47d84b6d82fede064b M      sha1dc


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Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[Ævar Arnfjörð Bjarmason]

On Sun, Jul 29 2018, Michael wrote:

> On 29/07/2018 20:10, brian m. carlson wrote:
>> On Sun, Jul 29, 2018 at 06:44:26PM +0200, Michael wrote:
>>> root@x066:[/tmp/xxx]git --version
>>> git version 2.13.3
>>> root@x066:[/tmp/xxx]git clone git@github.com:aixtools/hello-world.git
>>> Cloning into 'hello-world'...
>>> remote: Counting objects: 3, done.
>>> remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 3
>>> Receiving objects: 100% (3/3), done.
>>> fatal: pack is corrupted (SHA1 mismatch)
>>> fatal: index-pack failed
>>>
>>> p.s. - what surprises me re: git-2.13.2 - no messages about 'Cloning into
>>> ...', which version 2.13.1 did give.
>>>
>>> I guess a bisect is the next step - between version 2.13.2 and 2.13.3. Other
>>> suggestions welcome!
>> Are you using SHA1DC on that system, and does compiling with another
>> SHA-1 implementation help?  There was a change to the SHA1DC code big
>> endian detection in that commit, which might be the cause of your
>> problems if you're using a POWER or PowerPC system.
>
> I was thinking it might be an 'endian' issue. So, yes - AIX runs on
> POWER, only as BigEndian.
>
> git bisect returns:
>
> michael@x071:[/data/prj/aixtools/git/github/git-master]git bisect bad
> Bisecting: 1 revision left to test after this (roughly 1 step)
> [35049a2343948f686861e176a8c395f9f67da7b6] Merge branch
> 'aw/contrib-subtree-doc-asciidoctor' into maint
> michael@x071:[/data/prj/aixtools/git/github/git-master]git bisect good
> Bisecting: 0 revisions left to test after this (roughly 0 steps)
> [9936c1b52a39fa14fca04f937df3e75f7498ac66] sha1dc: update from upstream
>
>
> michael@x071:[/data/prj/aixtools/git/github/git-master]git bisect bad
> 9936c1b52a39fa14fca04f937df3e75f7498ac66 is the first bad commit
> commit 9936c1b52a39fa14fca04f937df3e75f7498ac66
> Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> Date: Sat Jul 1 22:05:45 2017 +0000
>
>  sha1dc: update from upstream
>
>  Update sha1dc from the latest version by the upstream maintainer[1].
>
>  See commit 6b851e536b ("sha1dc: update from upstream", 2017-06-06) for
>  the last update.
>
>  This solves the Big Endian detection on Solaris reported against
>  v2.13.2[2], hopefully without any regressions. A version of this has
>  been tested on two Solaris SPARC installations, Cygwin (by jturney on
>  cygwin@Freenode), and on numerous more boring systems (mainly
>  linux/x86_64). See [3] for a discussion of the implementation and
>  platform-specific issues.
>
>  See commit a0103914c2 ("sha1dc: update from upstream", 2017-05-20) and
>  6b851e536b ("sha1dc: update from upstream", 2017-06-06) for previous
>  attempts in the 2.13 series to address various compile-time feature
>  detection in this library.
>
>
> 1. https://github.com/cr-marcstevens/sha1collisiondetection/commit/19d97bf5af05312267c2e874ee6bcf584d9e9681
>
>
> 2. <CAKKM46tHq13XiW5C8sux3=PZ1VHSu_npG8ExfWwcPD7rkZkyRQ@mail.gmail.com>
> (https://public-inbox.org/git/CAKKM46tHq13XiW5C8sux3=PZ1VHSu_npG8ExfWwcPD7rkZkyRQ@mail.gmail.com/)
>
>  3. https://github.com/cr-marcstevens/sha1collisiondetection/pull/34
>
>  Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
>  Signed-off-by: Junio C Hamano <gitster@pobox.com>
>
> :040000 040000 a84797967fb742e4ca9618a641d53ce3a6c6589b
> 32efa656d78901da961e4a47d84b6d82fede064b M sha1dc

Sorry about that. As can be seen from those PRs and the "git log"
detecting whether something is big endian or not can be quite tricky, we
figured out how to do it on both BSD and Solaris, but apparently broke
AIX as a result.

You should be able to define -DSHA1DC_FORCE_LITTLEENDIAN or
-DSHA1DC_FORCE_BIGENDIAN (looks like you'll need the latter) to get the
latest version to compile, but I and upstream cr-marcstevens would be
very interested to know from someone who knows AIX how this broke.

Also, to you and anyone else with access to AIX: I'd be happy to figure
these issues out pro-actively if you give me a login to an AIX
machine. I promise not to do anything except compile/debug/test git on
it.

I used to have access to an AIX box through a previous job ages ago,
it's a very interesting OS and like with Solaris it's easy to discover a
lot of portability issues.

Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[Andreas Schwab]

On Jul 29 2018, Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:

> Also, to you and anyone else with access to AIX: I'd be happy to figure
> these issues out pro-actively if you give me a login to an AIX
> machine. I promise not to do anything except compile/debug/test git on
> it.

The GCC compile farm <http://gcc.gnu.org/wiki/CompileFarm> has a machine
running AIX, and is free to use for anyone working on free software.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[Michael]

On 29/07/2018 23:40, Andreas Schwab wrote:
> On Jul 29 2018, Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
>
>> Also, to you and anyone else with access to AIX: I'd be happy to figure
>> these issues out pro-actively if you give me a login to an AIX
>> machine. I promise not to do anything except compile/debug/test git on
>> it.
> The GCC compile farm <http://gcc.gnu.org/wiki/CompileFarm> has a machine
> running AIX, and is free to use for anyone working on free software.
My goal is less "to work on", more, "to package" and/or "to work with". 
Most others, including IBM, seem to use gcc as compiler - which is fine. 
However, on AIX I often see side-effects introduced by the GNU run-time 
environment needed on top of the xlc.rte provided as part of AIX.

In any case - my testing is using the xlc complier - so there are syntax 
differences. the compiler has many modes - by default I use 'xlc_r' that 
has the following default settings:
xlc_r:  use        = DEFLT_C
         crt        = /lib/crt0.o
         mcrt       = /lib/mcrt0.o
         gcrt       = /lib/gcrt0.o
         libraries  = -L/usr/vac/lib,-lxlopt,-lxlipa,-lxl,-lpthreads,-lc
         proflibs   = -L/lib/profiled,-L/usr/lib/profiled
         hdlibs     = -L/usr/vac/lib,-lhmd
         options    = 
-qlanglvl=extc99,-qcpluscmt,-qkeyword=inline,-qalias=ansi,-qthreaded,-D_THREAD_SAFE,-D__VACPP_MULTI__

DEFLT_C (for the curious, the default options is perhaps most 
interesting) is:
* common definitions

DEFLT_C:
         use           =DEFLT
         xlurt_cfg_path=/usr/vac/urt
         xlurt_cfg_name=urt_client.cfg

DEFLT_CPP:
         use           =DEFLT
         xlurt_cfg_path=/usr/vacpp/urt
         xlurt_cfg_name=urt_client.cfg

DEFLT:
         cppcomp   = /usr/vacpp/exe/xlCentry
         ccomp     = /usr/vac/exe/xlcentry
         code      = /usr/vac/exe/xlCcode
         cpp       = /usr/vac/exe/xlCcpp
         munch     = /usr/vacpp/exe/munch
         dis       = /usr/vac/exe/dis
         xlC       = /usr/vac/bin/xlc
         list      = /usr/vac/exe/xllist
         xslt      = /usr/vac/exe/XALAN
         transforms = /usr/vac/listings
         listlibs  = /usr/vac/lib
         cppinc    = /usr/vacpp/include
         ipa       = /usr/vac/exe/ipa
         cppfilt   = /usr/vacpp/bin/c++filt
         bolt      = /usr/vac/exe/bolt
         as        = /bin/as
         ld        = /bin/ld
         artool    = /bin/ar
         options   = 
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_AIX61,-D_IBMR2,-D_POWER
         options32 = -bpT:0x10000000,-bpD:0x20000000
         options32_bmaxdata = -bpT:0x10000000,-bpD:0x30000000
         options64 = -bpT:0x100000000,-bpD:0x110000000
         ldopt     = "b:o:e:u:R:H:Y:Z:L:T:A:k:j:"
         hdlibs    = -L/usr/vac/lib,-lhmd
         xlCcopt   = 
-qlanglvl=extc99,-qcpluscmt,-qkeyword=inline,-qalias=ansi
         crt_64    = /lib/crt0_64.o
         mcrt_64   = /lib/mcrt0_64.o
         gcrt_64   = /lib/gcrt0_64.o
         smplibraries = -lxlsmp
         palibraries  = -L/usr/vatools/lib,-lpahooks
         resexp     = /usr/vacpp/lib/res.exp
         genexports = /usr/vac/bin/CreateExportList
         vac_path   = /usr/vac
         vacpp_path = /usr/vacpp
         xlcmp_path = /usr/vac:/usr/vacpp
         xlc_c_stdinc   = /usr/vac/include:/usr/include
         xlc_cpp_stdinc = /usr/vacpp/include:/usr/include
         xlurt_msg_cat_name=vacumsg.cat
         __GNUC_MINOR__ = 3


>
> Andreas.
>

Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[Michael]

On 29/07/2018 21:27, brian m. carlson wrote:
> On Sun, Jul 29, 2018 at 08:59:39PM +0200, Michael wrote:
>> On 29/07/2018 20:10, brian m. carlson wrote:
>>> Are you using SHA1DC on that system, and does compiling with another
>>> SHA-1 implementation help?  There was a change to the SHA1DC code big
>>> endian detection in that commit, which might be the cause of your
>>> problems if you're using a POWER or PowerPC system.
>> I was thinking it might be an 'endian' issue. So, yes - AIX runs on POWER,
>> only as BigEndian.
> Well, that explains it.  I would recommend submitting a patch to
> https://github.com/cr-marcstevens/sha1collisiondetection, and the we can
> pull in the updated submodule with that fix.
Not sure I am smart enough to do that. I'll have to download, build, and 
see what it says.
>
> In the mean time, you could build using OpenSSL or the block SHA-1
> implementation, and switch back once things are in a good state.  I do
> recommend using SHA1DC for things long term, though, as attacks on SHA-1
> are only going to get better.
Any suggestions on where/how to do this?

root@x066:[/data/prj/aixtools/git/git-2.13.2]./configure --help | grep 
-i sha
   --sharedstatedir=DIR    modifiable architecture-independent data 
[PREFIX/com]
   --datarootdir=DIR       read-only arch.-independent data root 
[PREFIX/share]

root@x066:[/data/prj/aixtools/git/git-2.13.2]./configure --help | grep ssl
   --with-openssl          use OpenSSL library (default is YES)
                           ARG can be prefix for openssl library and 
headers

Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[brian m. carlson]

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On Sun, Jul 29, 2018 at 09:48:43PM +0200, Michael wrote:
> On 29/07/2018 21:27, brian m. carlson wrote:
> > Well, that explains it.  I would recommend submitting a patch to
> > https://github.com/cr-marcstevens/sha1collisiondetection, and the we can
> > pull in the updated submodule with that fix.
> Not sure I am smart enough to do that. I'll have to download, build, and see
> what it says.

The issue is that somewhere in lib/sha1.c, you need to cause
SHA1DC_BIGENDIAN to be set.  That means you need to figure out what
compiler macro might indicate that.  I can tell you that a POWER- or
PowerPC-specific one is going to be a bad choice unless it includes the
endianness, since those chips come in little-endian versions as well.

_AIX might be a fine choice if you know that it only ever runs on
big-endian chips.

> > In the mean time, you could build using OpenSSL or the block SHA-1
> > implementation, and switch back once things are in a good state.  I do
> > recommend using SHA1DC for things long term, though, as attacks on SHA-1
> > are only going to get better.
> Any suggestions on where/how to do this?
> 
> root@x066:[/data/prj/aixtools/git/git-2.13.2]./configure --help | grep -i
> sha
>   --sharedstatedir=DIR    modifiable architecture-independent data
> [PREFIX/com]
>   --datarootdir=DIR       read-only arch.-independent data root
> [PREFIX/share]
> 
> root@x066:[/data/prj/aixtools/git/git-2.13.2]./configure --help | grep ssl
>   --with-openssl          use OpenSSL library (default is YES)
>                           ARG can be prefix for openssl library and headers

If you're using configure, you can use --with-openssl, or
--with-openssl=PREFIX if your OpenSSL isn't in the standard location but
is instead in PREFIX.
-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204

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Re: git broken for AIX somewhere between 2.13.2 and 2.13.3

[Michael]

On 29/07/2018 22:06, brian m. carlson wrote:
> On Sun, Jul 29, 2018 at 09:48:43PM +0200, Michael wrote:
>> On 29/07/2018 21:27, brian m. carlson wrote:
>>> Well, that explains it.  I would recommend submitting a patch to
>>> https://github.com/cr-marcstevens/sha1collisiondetection, and the we can
>>> pull in the updated submodule with that fix.
>> Not sure I am smart enough to do that. I'll have to download, build, and see
>> what it says.
> The issue is that somewhere in lib/sha1.c, you need to cause
> SHA1DC_BIGENDIAN to be set.  That means you need to figure out what
> compiler macro might indicate that.
I remember - roughly - a few decades back - having an assignment to 
write code to determine endianness. PDP and VAC were different iirc, and 
many other micro-processors besides the 8088/8086/z85/68k/etc..

If you are looking for a compiler macro as a way to determine this - 
maybe you have one for gcc, but not for xlc. I do not know it - currently :)

> I can tell you that a POWER- or
> PowerPC-specific one is going to be a bad choice unless it includes the
> endianness, since those chips come in little-endian versions as well.
Actually, the POWER8 and POWER9 (and I expect all future versions) 
support both. There are not separate chips. Per virtual machine - a mode 
is determined during boot (virtual power on) e.g., SLES11 only ran in 
BigEndian and SLES12 only runs in LittleEndian. afaik, RHEL was 
supplying both BE and LE distributions. AIX, as an OS, only runs in BE 
mode, and I expect IBM i (was os/400) is also only running in BE.
>
> _AIX might be a fine choice if you know that it only ever runs on
> big-endian chips.
Do you mean just testing for _AIX. That would be very very easy - yes!
>>> In the mean time, you could build using OpenSSL or the block SHA-1
>>> implementation, and switch back once things are in a good state.  I do
>>> recommend using SHA1DC for things long term, though, as attacks on SHA-1
>>> are only going to get better.
>> Any suggestions on where/how to do this?
>>
>> root@x066:[/data/prj/aixtools/git/git-2.13.2]./configure --help | grep -i
>> sha
>>    --sharedstatedir=DIR    modifiable architecture-independent data
>> [PREFIX/com]
>>    --datarootdir=DIR       read-only arch.-independent data root
>> [PREFIX/share]
>>
>> root@x066:[/data/prj/aixtools/git/git-2.13.2]./configure --help | grep ssl
>>    --with-openssl          use OpenSSL library (default is YES)
>>                            ARG can be prefix for openssl library and headers
> If you're using configure, you can use --with-openssl, or
> --with-openssl=PREFIX if your OpenSSL isn't in the standard location but
> is instead in PREFIX.
I'll look in configure to see if it is not finding openssl. I was 
assuming it was found - as everything else using GNU "auto" tools find 
it okay. i.e., /var/lib/libssl.a, etc..

Tomorrow!

Is detecting endianness at compile-time unworkable?

[Ævar Arnfjörð Bjarmason]

On Sun, Jul 29 2018, Michael wrote:

> On 29/07/2018 22:06, brian m. carlson wrote:
>> On Sun, Jul 29, 2018 at 09:48:43PM +0200, Michael wrote:
>>> On 29/07/2018 21:27, brian m. carlson wrote:
>>>> Well, that explains it.  I would recommend submitting a patch to
>>>> https://github.com/cr-marcstevens/sha1collisiondetection, and the we can
>>>> pull in the updated submodule with that fix.
>>> Not sure I am smart enough to do that. I'll have to download, build, and see
>>> what it says.
>> The issue is that somewhere in lib/sha1.c, you need to cause
>> SHA1DC_BIGENDIAN to be set.  That means you need to figure out what
>> compiler macro might indicate that.
> I remember - roughly - a few decades back - having an assignment to
> write code to determine endianness. PDP and VAC were different iirc,
> and many other micro-processors besides the 8088/8086/z85/68k/etc..
>
> If you are looking for a compiler macro as a way to determine this -
> maybe you have one for gcc, but not for xlc. I do not know it - currently :)

I'm not familiar with AIX, but from searching around I found this
porting manual from IBM:
http://www.redbooks.ibm.com/redbooks/pdfs/sg246034.pdf

There they suggest either defining your own macros, or testing the
memory layout at runtime (see section "2.2.2.3 Technique 3: Testing
memory layout" and surrounding sections).

Perhaps it's worth taking a step back here and thinking about whether
this whole thing is unworkable. It was hard enough to get this to work
on the combination of Linux, *BSD and Solaris, but I suspect we'll run
into increasingly obscure platforms where this is hard or impossible
(AIX, HP/UX etc.)

The reason we're in this hole is because we use this
sha1collisiondetection library to do SHA-1, and the reason we have
issues with it specifically (not OpenSSL et al) is because its only
method of detecting endianness is at compile time.

This didn't use to be the case, it was changed in this commit:
https://github.com/cr-marcstevens/sha1collisiondetection/commit/d597672

Dan Shumow: Since the commit message doesn't say why, can you elaborate
a bit on why this was done, i.e. is determining this at runtime harmful
for performance? If not, perhaps it would be best to bring this back, at
least as an option.

And, as an aside, the reason we can't easily make it better ourselves is
because the build process for git.git doesn't have a facility to run
code to detect this type of stuff (the configure script is always
optional). So we can't just run this test ourselves.

Junio: I've barked up that particular tree before in
https://public-inbox.org/git/87a7x3kmh5.fsf@evledraar.gmail.com/ and I
won't bore you all by repeating myself, except to say that this is yet
another case where I wish we had a hard dependency on some way of doing
checks via compiled code in our build system.

Re: Is detecting endianness at compile-time unworkable?

[Junio C Hamano]

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

> And, as an aside, the reason we can't easily make it better ourselves is
> because the build process for git.git doesn't have a facility to run
> code to detect this type of stuff (the configure script is always
> optional). So we can't just run this test ourselves.

It won't help those who cross-compile anyway.  I thought we declared
"we make a reasonable effort to guess the target endianness from the
system header by inspecting usual macros, but will not aim to cover
every system on the planet---instead there is a knob to tweak it for
those on exotic platforms" last time we discussed this?

Re: Is detecting endianness at compile-time unworkable?

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>> And, as an aside, the reason we can't easily make it better ourselves is
>> because the build process for git.git doesn't have a facility to run
>> code to detect this type of stuff (the configure script is always
>> optional). So we can't just run this test ourselves.
>
> It won't help those who cross-compile anyway.  I thought we declared
> "we make a reasonable effort to guess the target endianness from the
> system header by inspecting usual macros, but will not aim to cover
> every system on the planet---instead there is a knob to tweak it for
> those on exotic platforms" last time we discussed this?

Well, having said all that, I do not think I personally mind if
./configure learned to include a "compile small program and run it
to determine byte order on the build machine" as part of "we make a
reasonable effort" as long as it cleanly excludes cross building
case (and the result is made overridable just in case we misdetect
the "cross-ness" of the build).

Re: Is detecting endianness at compile-time unworkable?

[Daniel Shumow]

[-- Attachment #1: Type: text/plain, Size: 1454 bytes --]

The change was definitely made for performance.  Removing the if
statements, conditioned upon endianess was an approx 10% improvement, which
was very important to getting this library accepted into git.

Thanks,
Dan


On Mon, Jul 30, 2018 at 11:32 AM, Junio C Hamano <gitster@pobox.com> wrote:

> Junio C Hamano <gitster@pobox.com> writes:
>
> > Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
> >
> >> And, as an aside, the reason we can't easily make it better ourselves is
> >> because the build process for git.git doesn't have a facility to run
> >> code to detect this type of stuff (the configure script is always
> >> optional). So we can't just run this test ourselves.
> >
> > It won't help those who cross-compile anyway.  I thought we declared
> > "we make a reasonable effort to guess the target endianness from the
> > system header by inspecting usual macros, but will not aim to cover
> > every system on the planet---instead there is a knob to tweak it for
> > those on exotic platforms" last time we discussed this?
>
> Well, having said all that, I do not think I personally mind if
> ./configure learned to include a "compile small program and run it
> to determine byte order on the build machine" as part of "we make a
> reasonable effort" as long as it cleanly excludes cross building
> case (and the result is made overridable just in case we misdetect
> the "cross-ness" of the build).
>
>

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Re: Is detecting endianness at compile-time unworkable?

[Michael Felt]

[-- Attachment #1: Type: text/plain, Size: 3396 bytes --]

I have just replied to 
https://github.com/cr-marcstevens/sha1collisiondetection/pull/42

I checked a gcc compiler on AIX, and I have the defines for vac.

I do not have access yet to SLES or RHEL (or Ubuntu), just a "free 
Debian" on my Power6.

* my conclusions|recommendations:

a) AIX is always Big Endian, the define _AIX can be used to determine if AIX

b) POWER7 and earlier are always Big Endian

c) assuming lscpu is always available on Linux systems a command (in 
configure?) could be used:

root@x074:/usr/bin# lscpu | grep -i endian
Byte Order:            Big Endian

d) some linux systems (in any case latest versions of RHEL and SLES 
enterprise) should have a file named lparcfg in /proc 
(/proc/{powerppc|ppc64|ppc64le|ppc64el}/lparcfg - and it might be in 
that file. Need to get onto a (POWER8|POWER9) system to check.

Hope this helps:

details re: define of _AIX

root@x068:[/data/httpd/gcc]gcc -dM -E - < /dev/null | grep AIX | head -1
#define _AIX 1

michael@x071:[/home/michael]/usr/bin/grep -p DEFLT: 
/etc/vac.cfg.[567][123] | grep options\
         options   = 
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_IBMR2,-D_POWER
         options   = 
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_AIX61,-D_IBMR2,-D_POWER
         options   = 
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_AIX61,-D_AIX71,-D_IBMR2,-D_POWER
         options   = 
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_AIX61,-D_AIX71,-D_AIX72,-D_IBMR2,-D_POWER

michael@x071:[/home/michael]ls /etc/vac.cfg.[567][123]
/etc/vac.cfg.53  /etc/vac.cfg.61  /etc/vac.cfg.71  /etc/vac.cfg.72


On 7/30/2018 8:39 PM, Daniel Shumow wrote:
> The change was definitely made for performance. Removing the if 
> statements, conditioned upon endianess was an approx 10% improvement, 
> which was very important to getting this library accepted into git.
>
> Thanks,
> Dan
>
>
> On Mon, Jul 30, 2018 at 11:32 AM, Junio C Hamano <gitster@pobox.com 
> <mailto:gitster@pobox.com>> wrote:
>
>     Junio C Hamano <gitster@pobox.com <mailto:gitster@pobox.com>> writes:
>
>     > Ævar Arnfjörð Bjarmason <avarab@gmail.com
>     <mailto:avarab@gmail.com>> writes:
>     >
>     >> And, as an aside, the reason we can't easily make it better
>     ourselves is
>     >> because the build process for git.git doesn't have a facility
>     to run
>     >> code to detect this type of stuff (the configure script is always
>     >> optional). So we can't just run this test ourselves.
>     >
>     > It won't help those who cross-compile anyway.  I thought we declared
>     > "we make a reasonable effort to guess the target endianness from the
>     > system header by inspecting usual macros, but will not aim to cover
>     > every system on the planet---instead there is a knob to tweak it for
>     > those on exotic platforms" last time we discussed this?
>
>     Well, having said all that, I do not think I personally mind if
>     ./configure learned to include a "compile small program and run it
>     to determine byte order on the build machine" as part of "we make a
>     reasonable effort" as long as it cleanly excludes cross building
>     case (and the result is made overridable just in case we misdetect
>     the "cross-ness" of the build).
>
>


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Re: Is detecting endianness at compile-time unworkable?

[Eric Wong]

Junio C Hamano <gitster@pobox.com> wrote:
> Well, having said all that, I do not think I personally mind if
> ./configure learned to include a "compile small program and run it
> to determine byte order on the build machine" as part of "we make a
> reasonable effort" as long as it cleanly excludes cross building
> case (and the result is made overridable just in case we misdetect
> the "cross-ness" of the build).

No need to run the program for cross-compiles, grepping a object
file seems to work for autoconf:

	git clone https://git.sv.gnu.org/git/autoconf.git
	$PAGER autoconf/lib/autoconf/c.m4
	# look for "BIGenDianSyS"

Re: Is detecting endianness at compile-time unworkable?

[Ævar Arnfjörð Bjarmason]

On Mon, Jul 30 2018, Junio C Hamano wrote:

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>> And, as an aside, the reason we can't easily make it better ourselves is
>> because the build process for git.git doesn't have a facility to run
>> code to detect this type of stuff (the configure script is always
>> optional). So we can't just run this test ourselves.
>
> It won't help those who cross-compile anyway.

I was being unclear, what I mean by having "a hard dependency on some
way of doing checks via compiled code in our build system" is that we
would do some equivalent of this:

    diff --git a/Makefile b/Makefile
    index 08e5c54549..b021b6e1b6 100644
    --- a/Makefile
    +++ b/Makefile
    @@ -1107,7 +1107,7 @@ DC_SHA1_SUBMODULE = auto
     endif

     include config.mak.uname
    --include config.mak.autogen
    +include config.mak.autogen
     -include config.mak

     ifdef DEVELOPER

And document that in order to build git you needed to do './configure &&
make' instead of just 'make', and we'd error out by default if
config.mak.autogen wasn't there.

Now obviously that would need some sort of escape hatch. I.e. you could
invoke 'make' like this:

    make CONFIGURE_MAK_AUTOGEN_FILE=some-file

That's how you would do cross-compilation, you'd arrange to run
'./configure' on some system, save the output, and ferry over this
'some-file' to where you're building git, or you would manually prepare
a file that had all the settings we'd expect to have been set already
set.

Now, whether we do this with autoconf or not is just an implementation
detail. Looking at this some more I think since we already use the
$(shell) construct we could just have some 'configure-detect' Makefile
target which would compile various test programs, and we'd use their
output to set various settings, a sort of home-grown autoconf (because
people are bound to have objections to a hard dependency on it...).

> I thought we declared "we make a reasonable effort to guess the target
> endianness from the system header by inspecting usual macros, but will
> not aim to cover every system on the planet---instead there is a knob
> to tweak it for those on exotic platforms" last time we discussed
> this?

Yes, but I think it's worth re-visiting that decision, which was made
with the constraints that we don't have a build system that can do
checks via compiled code, so we need this hack in the first place
instead of things Just Working.

And as I pointed out in the linked E-Mail this also impacts us in other
ways, and will cause other issues in the future, so it's worth thinking
about if this is the right path to take.

Re: Is detecting endianness at compile-time unworkable?

[Michael Felt]

A small step back...


On 7/30/2018 11:39 AM, Ævar Arnfjörð Bjarmason wrote:
> On Sun, Jul 29 2018, Michael wrote:
>
>> On 29/07/2018 22:06, brian m. carlson wrote:
>>> On Sun, Jul 29, 2018 at 09:48:43PM +0200, Michael wrote:
>>>> On 29/07/2018 21:27, brian m. carlson wrote:
>>>>> Well, that explains it.  I would recommend submitting a patch to
>>>>> https://github.com/cr-marcstevens/sha1collisiondetection, and the we can
>>>>> pull in the updated submodule with that fix.
>>>> Not sure I am smart enough to do that. I'll have to download, build, and see
>>>> what it says.
>>> The issue is that somewhere in lib/sha1.c, you need to cause
>>> SHA1DC_BIGENDIAN to be set.  That means you need to figure out what
>>> compiler macro might indicate that.
>> I remember - roughly - a few decades back - having an assignment to
>> write code to determine endianness. PDP and VAC were different iirc,
>> and many other micro-processors besides the 8088/8086/z85/68k/etc..
>>
>> If you are looking for a compiler macro as a way to determine this -
>> maybe you have one for gcc, but not for xlc. I do not know it - currently :)
> I'm not familiar with AIX, but from searching around I found this
> porting manual from IBM:
> http://www.redbooks.ibm.com/redbooks/pdfs/sg246034.pdf
This is from July 2001 - when AIX 5L, for Linux affinity, was new. AIX 
was (nearly) the #1 posix system, and linux was a minor player in the 
data center (in or out (now as IAAS)). IMHO, the recommendations made in 
2001 are probably no longer applicable (64-bit was fairly new, e.g., 
rather than common).
>
> There they suggest either defining your own macros, or testing the
> memory layout at runtime (see section "2.2.2.3 Technique 3: Testing
> memory layout" and surrounding sections).
>
> Perhaps it's worth taking a step back here and thinking about whether
> this whole thing is unworkable. It was hard enough to get this to work
> on the combination of Linux, *BSD and Solaris, but I suspect we'll run
> into increasingly obscure platforms where this is hard or impossible
> (AIX, HP/UX etc.)
>
> The reason we're in this hole is because we use this
> sha1collisiondetection library to do SHA-1, and the reason we have
> issues with it specifically (not OpenSSL et al) is because its only
> method of detecting endianness is at compile time.
Cannot speak for the "others", but as I have mentioned before - as AIX 
in only on POWER it is also only Big Endian - so a compiletime #if 
testing for _AIX will work fine
> This didn't use to be the case, it was changed in this commit:
> https://github.com/cr-marcstevens/sha1collisiondetection/commit/d597672
>
> Dan Shumow: Since the commit message doesn't say why, can you elaborate
> a bit on why this was done, i.e. is determining this at runtime harmful
> for performance? If not, perhaps it would be best to bring this back, at
> least as an option.
>
> And, as an aside, the reason we can't easily make it better ourselves is
> because the build process for git.git doesn't have a facility to run
> code to detect this type of stuff (the configure script is always
> optional). So we can't just run this test ourselves.
On AIX - I am required to run configure, and frankly, I am amazed that 
not everyone is running it. Among other things I an modifying the prefix 
(to /opt) and many of the others to different /var/git/* areas as I do 
not want to "polute" the BOS (base OS) and/or other packages/packagers. 
Officially, according the Linux FHS-3.0 I sould be using /opt/aixtools 
as prefix.

FYI: my current build process is:
wget git-{version}.tar.xz
xz -dc git-{version}.tar.xz
cd git-{version}.tar.xz
mv Makefile Makefile.git #my build scripts only run configure when 
Makefile does not exist
./configure ...
ln Makefile.git Makefile
make

I am amazed, as it rarely happens (maybe git is my first encounter) - 
that configure does not create a Makefile. This also complicates 
building git "out of tree".
>
> Junio: I've barked up that particular tree before in
> https://public-inbox.org/git/87a7x3kmh5.fsf@evledraar.gmail.com/ and I
> won't bore you all by repeating myself, except to say that this is yet
> another case where I wish we had a hard dependency on some way of doing
> checks via compiled code in our build system.
For AIX: again - the determination is simple. If _AIX is set to 1 then 
use BigEndian, or, use:
michael@x071:[/home/michael]uname
AIX
  i.e., something like:
$(uname) == "AIX" && BigEndian=1

Re: Is detecting endianness at compile-time unworkable?

[Ævar Arnfjörð Bjarmason]

On Tue, Jul 31 2018, Michael Felt wrote:

> For AIX: again - the determination is simple. If _AIX is set to 1 then
> use BigEndian, or, use:
> michael@x071:[/home/michael]uname
> AIX
> i.e., something like:
> $(uname) == "AIX" && BigEndian=1

In lieu of some "let's test this with a compile-test" solution, that
seems like a viable way forward for now. Can you please test the merge
request I have at
https://github.com/cr-marcstevens/sha1collisiondetection/pull/45 by
manually applying that change to the relevant file in sha1dc/ and
building/testing git on AIX?

It should work, but as noted in the MR please test it so we can make
sure, and then (if you have a GitHub account) comment on the MR saying
it works for you.

[PATCH] sha1dc: update from upstream

[Ævar Arnfjörð Bjarmason]

Update sha1dc from the latest version by the upstream
maintainer[1]. See 2db87328ef ("Merge branch 'ab/sha1dc'", 2017-07-10)
for the last update.

This fixes an issue where AIX was wrongly detected as a Little-endian
instead of a Big-endian system. See [2][3][4].

1. https://github.com/cr-marcstevens/sha1collisiondetection/commit/232357eb2ea0397388254a4b188333a227bf5b10
2. https://github.com/cr-marcstevens/sha1collisiondetection/pull/45
3. https://github.com/cr-marcstevens/sha1collisiondetection/pull/42
4. https://public-inbox.org/git/20180729200623.GF945730@genre.crustytoothpaste.net/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

On Wed, Aug 01 2018, Ævar Arnfjörð Bjarmason wrote:
> https://github.com/cr-marcstevens/sha1collisiondetection/pull/45
>[...]
> It should work, but as noted in the MR please test it so we can make
> sure, and then (if you have a GitHub account) comment on the MR saying
> it works for you.

This got merged upstream, and as noted in that upstream PR I've
personally tested this on AIX under both GCC and IBM's xlc on the GCC
compile farm, it works.

 sha1collisiondetection |  2 +-
 sha1dc/sha1.c          | 12 +++++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/sha1collisiondetection b/sha1collisiondetection
index 19d97bf5af..232357eb2e 160000
--- a/sha1collisiondetection
+++ b/sha1collisiondetection
@@ -1 +1 @@
-Subproject commit 19d97bf5af05312267c2e874ee6bcf584d9e9681
+Subproject commit 232357eb2ea0397388254a4b188333a227bf5b10
diff --git a/sha1dc/sha1.c b/sha1dc/sha1.c
index 25eded1399..df0630bc6d 100644
--- a/sha1dc/sha1.c
+++ b/sha1dc/sha1.c
@@ -93,13 +93,23 @@
 #define SHA1DC_BIGENDIAN
 
 /* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist> */
+#elif (defined(_AIX))
+
+/*
+ * Defines Big Endian on a whitelist of OSs that are known to be Big
+ * Endian-only. See
+ * https://public-inbox.org/git/93056823-2740-d072-1ebd-46b440b33d7e@felt.demon.nl/
+ */
+#define SHA1DC_BIGENDIAN
+
+/* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist> or <os whitelist> */
 #elif defined(SHA1DC_ON_INTEL_LIKE_PROCESSOR)
 /*
  * As a last resort before we do anything else we're not 100% sure
  * about below, we blacklist specific processors here. We could add
  * more, see e.g. https://wiki.debian.org/ArchitectureSpecificsMemo
  */
-#else /* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist>  or <processor blacklist> */
+#else /* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist> or <os whitelist> or <processor blacklist> */
 
 /* We do nothing more here for now */
 /*#error "Uncomment this to see if you fall through all the detection"*/
-- 
2.18.0.345.g5c9ce644c3

Re: [PATCH] sha1dc: update from upstream

[Michael Felt (aixtools)]

Sent from my iPhone

> On 2 Aug 2018, at 22:50, Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
> 
> Update sha1dc from the latest version by the upstream
> maintainer[1]. See 2db87328ef ("Merge branch 'ab/sha1dc'", 2017-07-10)
> for the last update.
> 
> This fixes an issue where AIX was wrongly detected as a Little-endian
> instead of a Big-endian system. See [2][3][4].
> 
> 1. https://github.com/cr-marcstevens/sha1collisiondetection/commit/232357eb2ea0397388254a4b188333a227bf5b10
> 2. https://github.com/cr-marcstevens/sha1collisiondetection/pull/45
> 3. https://github.com/cr-marcstevens/sha1collisiondetection/pull/42
> 4. https://public-inbox.org/git/20180729200623.GF945730@genre.crustytoothpaste.net/
> 
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
> 
>> On Wed, Aug 01 2018, Ævar Arnfjörð Bjarmason wrote:
>> https://github.com/cr-marcstevens/sha1collisiondetection/pull/45
>> [...]
>> It should work, but as noted in the MR please test it so we can make
>> sure, and then (if you have a GitHub account) comment on the MR saying
>> it works for you.
> 
> This got merged upstream, and as noted in that upstream PR I've
> personally tested this on AIX under both GCC and IBM's xlc on the GCC
> compile farm, it works.
> 
Thanks. I already have git 2.18 in use with the manual patch. 
> sha1collisiondetection |  2 +-
> sha1dc/sha1.c          | 12 +++++++++++-
> 2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/sha1collisiondetection b/sha1collisiondetection
> index 19d97bf5af..232357eb2e 160000
> --- a/sha1collisiondetection
> +++ b/sha1collisiondetection
> @@ -1 +1 @@
> -Subproject commit 19d97bf5af05312267c2e874ee6bcf584d9e9681
> +Subproject commit 232357eb2ea0397388254a4b188333a227bf5b10
> diff --git a/sha1dc/sha1.c b/sha1dc/sha1.c
> index 25eded1399..df0630bc6d 100644
> --- a/sha1dc/sha1.c
> +++ b/sha1dc/sha1.c
> @@ -93,13 +93,23 @@
> #define SHA1DC_BIGENDIAN
> 
> /* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist> */
> +#elif (defined(_AIX))
> +
> +/*
> + * Defines Big Endian on a whitelist of OSs that are known to be Big
> + * Endian-only. See
> + * https://public-inbox.org/git/93056823-2740-d072-1ebd-46b440b33d7e@felt.demon.nl/
> + */
> +#define SHA1DC_BIGENDIAN
> +
> +/* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist> or <os whitelist> */
> #elif defined(SHA1DC_ON_INTEL_LIKE_PROCESSOR)
> /*
>  * As a last resort before we do anything else we're not 100% sure
>  * about below, we blacklist specific processors here. We could add
>  * more, see e.g. https://wiki.debian.org/ArchitectureSpecificsMemo
>  */
> -#else /* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist>  or <processor blacklist> */
> +#else /* Not under GCC-alike or glibc or *BSD or newlib or <processor whitelist> or <os whitelist> or <processor blacklist> */
> 
> /* We do nothing more here for now */
> /*#error "Uncomment this to see if you fall through all the detection"*/
> -- 
> 2.18.0.345.g5c9ce644c3
> 

Re: [PATCH] sha1dc: update from upstream

[Stefan Beller]

On Thu, Aug 2, 2018 at 1:51 PM Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:

> diff --git a/sha1collisiondetection b/sha1collisiondetection
> index 19d97bf5af..232357eb2e 160000
> --- a/sha1collisiondetection
> +++ b/sha1collisiondetection
> @@ -1 +1 @@
> -Subproject commit 19d97bf5af05312267c2e874ee6bcf584d9e9681
> +Subproject commit 232357eb2ea0397388254a4b188333a227bf5b10

Offtopic:
I wonder if we want to extend diffs a little here and similar to a diffstat
that is not technically needed, but rather aiding the reviewers eyes.
So maybe we could add a concise shortlog, e.g. after this line:

19d97bf5..232357eb (2 dots indicating it is a fast forward instead of 3 dots)
3 commits from "Merge pull request #37 from avar/fixup-pull-request-34"
to "Merge pull request #45 from avar/aix-big-endian-detection"

Re: Is detecting endianness at compile-time unworkable?

[Michael Felt]

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On 7/30/2018 11:39 AM, Ævar Arnfjörð Bjarmason wrote:
> The reason we're in this hole is because we use this
> sha1collisiondetection library to do SHA-1, and the reason we have
> issues with it specifically (not OpenSSL et al) is because its only
> method of detecting endianness is at compile time.
When using gcc (no xlc available for Linux on Power)

POWER6 (Big Endian by definition)
root@x068:[/data/httpd/gcc]gcc -dM -E - < /dev/null | grep -i end
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __BIG_ENDIAN__ 1
#define __FLOAT_WORD_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define _BIG_ENDIAN 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__

SLES12 on POWER8
suse12test:~ # gcc -dM -E - < /dev/null | grep -i end
#define __ORDER_LITTLE_ENDIAN__ 1234
#define _LITTLE_ENDIAN 1
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__

*So, for compile time tests, when gcc is the compiler it seems the
following defines are available**
**__BIG_ENDIAN__, _BIG_ENDIAN,  __LITTLE__ENDIAN__, _LITTLE_ENDIAN**
**or something based on the value of __BYTE_ORDER__*

I'll see if I can find something similar for xlc, but will only be able
to test xlc on AIX.

>
> This didn't use to be the case, it was changed in this commit:
> https://github.com/cr-marcstevens/sha1collisiondetection/commit/d597672
>
> Dan Shumow: Since the commit message doesn't say why, can you elaborate
> a bit on why this was done, i.e. is determining this at runtime harmful
> for performance? If not, perhaps it would be best to bring this back, at
> least as an option.


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Re: Is detecting endianness at compile-time unworkable?

[Michael Felt]

I hope a I have a "leap forward"


On 7/30/2018 11:39 AM, Ævar Arnfjörð Bjarmason wrote:
> Perhaps it's worth taking a step back here and thinking about whether
> this whole thing is unworkable. It was hard enough to get this to work
> on the combination of Linux, *BSD and Solaris, but I suspect we'll run
> into increasingly obscure platforms where this is hard or impossible
> (AIX, HP/UX etc.)
While I still cannot say for HP/UX it does seem there is a potential
solution based on the status for _LITTLE_ENDIAN and _BIG_ENDIAN. At
least, gcc on POWER and xlc on POWER provides one or the other - and my
hope is that gcc on other platforms also provides them.

For "other" compilers that do not provide them - a modification to
CFLAGS to define one or the other should make "make" work.

Details (note - I am not a programmer, so by definition at least one of
my "macros" will be wrong :)

AIX and xlc
root@x066:[/]xlc   -qshowmacros -E /dev/null | grep -i endi
1506-297 (S) Unable to open input file null. A file or directory in the
path name does not exist..
#define __HHW_BIG_ENDIAN__ 1
#define __BIG_ENDIAN__ 1
#define __THW_BIG_ENDIAN__ 1
#define _BIG_ENDIAN 1

On SLES12 (le) and xlc
suse12test:~/images/littleEndian/sles # xlc -qshowmacros -dM -E x.c |
grep -i endi
#define _LITTLE_ENDIAN 1
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
#define __VEC_ELEMENT_REG_ORDER__ __ORDER_LITTLE_ENDIAN__


Based on what I can see on gcc on POWER and xlc on POWER I think an
approach (simplified) can be:

#if undefined(_BIG_ENDIAN) && undef(_LITTLE_ENDIAN)
#error "one of _BIG_ENDIAN or _LITTLE_ENDIAN must be defined. Try adding
the correct value to CFLAGS"
#else defined(_BIG_ENDIAN) && defined(_LITTLE_ENDIAN)
#error "Only one of _BIG_ENDIAN and _LITTLE_ENDIAN may be defined, not both"
#endif

And then logic based on the value set.
This should also make cross-compile possible by unsetting an incorrect
default and setting the correct value.

p.s. Is there a setting I need to set somewhere so I receive a copy of
the email sent after it is received by the list. I could send myself a
copy, but I much prefer it comes from the maillist - as verification it
was received.

Re: Is detecting endianness at compile-time unworkable?

[Ævar Arnfjörð Bjarmason]

On Tue, Jul 31 2018, Michael Felt wrote:

> I hope a I have a "leap forward"
>
>
> On 7/30/2018 11:39 AM, Ævar Arnfjörð Bjarmason wrote:
>> Perhaps it's worth taking a step back here and thinking about whether
>> this whole thing is unworkable. It was hard enough to get this to work
>> on the combination of Linux, *BSD and Solaris, but I suspect we'll run
>> into increasingly obscure platforms where this is hard or impossible
>> (AIX, HP/UX etc.)
> While I still cannot say for HP/UX it does seem there is a potential
> solution based on the status for _LITTLE_ENDIAN and _BIG_ENDIAN. At
> least, gcc on POWER and xlc on POWER provides one or the other - and my
> hope is that gcc on other platforms also provides them.

Yeah with GCC this is relatively easy, see
https://github.com/cr-marcstevens/sha1collisiondetection/blame/c3e1304/lib/sha1.c#L29-L115

> For "other" compilers that do not provide them - a modification to
> CFLAGS to define one or the other should make "make" work.
>
> Details (note - I am not a programmer, so by definition at least one of
> my "macros" will be wrong :)
>
> AIX and xlc
> root@x066:[/]xlc -qshowmacros -E /dev/null | grep -i endi
> 1506-297 (S) Unable to open input file null. A file or directory in the
> path name does not exist..
> #define __HHW_BIG_ENDIAN__ 1
> #define __BIG_ENDIAN__ 1
> #define __THW_BIG_ENDIAN__ 1
> #define _BIG_ENDIAN 1
>
> On SLES12 (le) and xlc
> suse12test:~/images/littleEndian/sles # xlc -qshowmacros -dM -E x.c |
> grep -i endi
> #define _LITTLE_ENDIAN 1
> #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
> #define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
> #define __LITTLE_ENDIAN__ 1
> #define __ORDER_BIG_ENDIAN__ 4321
> #define __ORDER_LITTLE_ENDIAN__ 1234
> #define __ORDER_PDP_ENDIAN__ 3412
> #define __VEC_ELEMENT_REG_ORDER__ __ORDER_LITTLE_ENDIAN__
>
>
> Based on what I can see on gcc on POWER and xlc on POWER I think an
> approach (simplified) can be:
>
> #if undefined(_BIG_ENDIAN) && undef(_LITTLE_ENDIAN)
> #error "one of _BIG_ENDIAN or _LITTLE_ENDIAN must be defined. Try adding
> the correct value to CFLAGS"
> #else defined(_BIG_ENDIAN) && defined(_LITTLE_ENDIAN)
> #error "Only one of _BIG_ENDIAN and _LITTLE_ENDIAN may be defined, not both"
> #endif
>
> And then logic based on the value set.
> This should also make cross-compile possible by unsetting an incorrect
> default and setting the correct value.

...the real trick is using these macros outside of GCC / glibc and on
older GCC versions. See the github link above, you basically end up with
a whitelist of how it looks on different systems / compilers. Sometimes
both are defined, sometimes only both etc.

It can be done, but as that code shows it's somewhat complex macro soup
to get right.

> p.s. Is there a setting I need to set somewhere so I receive a copy of
> the email sent after it is received by the list. I could send myself a
> copy, but I much prefer it comes from the maillist - as verification it
> was received.

You should get that, but maybe your mailer ignores Message-Ids it
already has, but you can go to https://public-inbox.org/git/ and search
for the Message-Id or your name to see E-Mails you've sent that made it
to the list, e.g.:
https://public-inbox.org/git/?q=aixtools%40felt.demon.nl

Re: Is detecting endianness at compile-time unworkable?

[Michael]

On 31/07/2018 16:25, Ævar Arnfjörð Bjarmason wrote:
> ...the real trick is using these macros outside of GCC / glibc and on
> older GCC versions. See the github link above, you basically end up with
> a whitelist of how it looks on different systems / compilers. Sometimes
> both are defined, sometimes only both etc.
>
> It can be done, but as that code shows it's somewhat complex macro soup
> to get right.

FYI - the gcc I was using is 4.7.4.

And, the reason I suggest the test for both not being defined is so that 
'make' stops and whoever is running make just sets one or the other. Let 
them 'file a bug' When they come with a compiler that does not work - 
and find out what could be used.

For example, _AIX is the same as _BIG_ENDIAN. In the meantime, the code 
to test is simple.

Either one of _BIG_ENDIAN or _LITTLE_ENDIAN is provided by the compiler 
or the builder supplies one of the two using CFLAGS. I assume there is 
also a "undefine" flag, maybe -U - so hopefully a -U and a -D 
combination could be used for cross-compiling.

re: my mailer blocking things - it would only be for this list, as other 
lists come through with no extra work from me. At least I am not aware 
of anything special I could do.