Re: Trying Debian/armhf rebootstrap with time64

Re: Trying Debian/armhf rebootstrap with time64

[Arnd Bergmann]

[some mailing lists appear to have classified the earlier mail as spam,
 it was quite long and contained a lot of links. See
 https://lists.debian.org/debian-arm/2020/03/msg00032.html for the
 start of the thread if you did not get that]

On Wed, Mar 11, 2020 at 3:37 PM Lukasz Majewski <lukma@denx.de> wrote:
> >   - stat()/fstat()/lstat(), nanosleep(), wait3()/wait4(), ppoll_chk()
> >     are some of the other interfaces that take a time_t based
> >     argument and need to grow a time64 version to avoid an ABI
> > mismatch.
>
> The stat() and friends will use statx internally, which supports 64 bit
> time from the outset.
> Unfortunately, it hasn't been yet converted.
>
> As statx was added in 4.1 (IIRC) - after the minimal supported Linux
> kernel version is bumped to this version (from 3.2 as now) it all will
> be fixed.

The problem I had with these was not on the kernel API side (I
still have CONFIG_COMPAT_32BIT_TIME enabled for now) but
on the application side. In particular, the 'struct stat' definition
(when __USE_XOPEN2K8 is defined) contains

         struct timespec st_atim;

and similar fields that are interpreted using 64-bit time_t in the
application including the header, but with 32-bit time_t inside of
the ___fxstat64() implementation in glibc. The problem is caused
by the mismatched ABI, not by the time_t overflow, in the same
way that happens in the nptl library callers and in the other interfaces
I mentioned.
This is also what seems to cause most of the testcase failures
when the tests are built with __TIME_BITS=64.

> >   - The timeval prototype appears to be broken, as it's missing
> >     padding on architectures without native alignment of __time64
> >     (e.g. i386) and on all big-endian architectures.
> >
>
> You mean the one "exported" to the system or one, which is internal to
> glibc (from ./include/time.h)?

I mean in the installed headers, where I get (after preprocessing)

typedef long long __time64_t;
typedef long __suseconds_t;
struct timeval
{
  __time64_t tv_sec;
  __suseconds_t tv_usec;
};

On i386 and m68k, this leads to a 12 byte structure when the kernel
interfaces expect a 16 byte structure. All other 32-bit architectures add
four byte padding at the end, so the size is correct, but on big-endian
systems, kernel also expects padding *before* tv_usec, in the same
way as the timespec definition does. IIRC the best way to handle this
is with a 64-bit suseconds_t, e.g.  by adding a __suseconds64_t
defined the same way as __time64_t.

> > I have spent more time on this now than I had planned, and don't
> > expect to do further work on it anytime soon, but I hope my summary
> > is useful to others that are going to need this later.  I can
> > obviously share my patches and build artifacts if anyone needs them.
>
> Could you upload them to any server? (kernel.org or github)?

I have uploaded the modified debian-glibc and rebootstrap
sources to https://git.linaro.org/people/arnd/ now, this should
be all that's needed to recreate the build, using these steps:

- build an x86-64 debian glibc-2.31 package (binary plus source)
  based on the glibc package data
- create a pbuilder instance with that available as a source to apt
- log into the pbuilder and run the modified bootstrap.sh according
  to information on the pbuilder web page.

The binary packages I created are not as useful, as they would
not work with any build of glibc, neither the version I built, nor
any fixed one. I could find a way to send that to you in private,
but it's hundreds of megabytes.

Unfortunately I lost the build logs during a crash yesterday.

> > There are two additional approaches that would likely get a Debian
> > bootstrap further, but that I have not tried as they were previously
> > dismissed:
> >
> > * Adding a time64 armhf as a separate (incompatible) target in glibc
> >   that defines __TIMESIZE==64 and a 64-bit __time_t would avoid
> >   most of the remaining ABI issues and put armhf-time64 in the same
> >   category as riscv32 and arc, but this idea was so far rejected by
> > the glibc maintainers.
>
> As fair as I know riscv32 and arc will use generic syscall interface.
> The arm32 bit doesn't support it - so the code from those two
> aforementioned ports will not be used.

The differences between the generic syscall interface and the arm
version are much smaller than ABI differences between the ABIs
for 32-bit __time_t and the __time_t == __time64_t version.

In particular, as such a new port could mandate a minimum kernel
of v5.1, it could just use all the time64 syscalls, the split sysvipc
and statx as a baseline.

      Arnd

Re: [Y2038] Trying Debian/armhf rebootstrap with time64

[Ben Hutchings]

On Mon, 2020-03-16 at 16:02 +0100, Arnd Bergmann wrote:
> On Mon, Mar 16, 2020 at 3:47 PM Rich Felker <dalias@libc.org> wrote:
> 
> > libtirpc is the replacement. I wasn't aware if uses libc-provided rpc
> > headers (presumably only if they exist, since folks are using it fine
> > on musl) but even if so I think the types will automatically update
> > when time_t changes. Of course that leaves the libtirpc ABI dependent
> > on which time_t is used.
> 
> Ok, makes sense. I suppose it just provides a header with the same
> name then.

* nfs-utils build-depends on libtirpc-dev, and isn't using the glibc
SunRPC headers except for <rpc/netdb.h>.  libtirpc's <rpc/rpcent.h>
specifically avoids declaring things that are also declared in glibc's
<rpc/netdb.h>.

* ntirpc is a different port of the SunRPC code, used by nfs-ganesha.

* nis and nfswatch really are using the glibc SunRPC headers.

Ben.

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom

Re: [Y2038] Trying Debian/armhf rebootstrap with time64

[Florian Weimer]

* Ben Hutchings:

> On Mon, 2020-03-16 at 16:02 +0100, Arnd Bergmann wrote:
>> On Mon, Mar 16, 2020 at 3:47 PM Rich Felker <dalias@libc.org> wrote:
>> 
>> > libtirpc is the replacement. I wasn't aware if uses libc-provided rpc
>> > headers (presumably only if they exist, since folks are using it fine
>> > on musl) but even if so I think the types will automatically update
>> > when time_t changes. Of course that leaves the libtirpc ABI dependent
>> > on which time_t is used.
>> 
>> Ok, makes sense. I suppose it just provides a header with the same
>> name then.
>
> * nfs-utils build-depends on libtirpc-dev, and isn't using the glibc
> SunRPC headers except for <rpc/netdb.h>.  libtirpc's <rpc/rpcent.h>
> specifically avoids declaring things that are also declared in glibc's
> <rpc/netdb.h>.
>
> * ntirpc is a different port of the SunRPC code, used by nfs-ganesha.
>
> * nis and nfswatch really are using the glibc SunRPC headers.

Which part of NIS?  There's a new upstream for libnsl
<https://github.com/thkukuk/libnsl> and the NSS module
<https://github.com/thkukuk/libnss_nis>.  (There is a nisplus module
as well.)

All these use libtirpc and support IPv6 in addition to IPv4.  As far
as I know, it is possible to build a full NIS stack without relying on
any of the legacy glibc code.

(I don't know about nfswatch.)

Re: [Y2038] Trying Debian/armhf rebootstrap with time64

[Ben Hutchings]

On Fri, 2020-03-20 at 00:09 +0100, Florian Weimer wrote:
> * Ben Hutchings:
> 
> > On Mon, 2020-03-16 at 16:02 +0100, Arnd Bergmann wrote:
> > > On Mon, Mar 16, 2020 at 3:47 PM Rich Felker <dalias@libc.org> wrote:
> > > 
> > > > libtirpc is the replacement. I wasn't aware if uses libc-provided rpc
> > > > headers (presumably only if they exist, since folks are using it fine
> > > > on musl) but even if so I think the types will automatically update
> > > > when time_t changes. Of course that leaves the libtirpc ABI dependent
> > > > on which time_t is used.
> > > 
> > > Ok, makes sense. I suppose it just provides a header with the same
> > > name then.
> > 
> > * nfs-utils build-depends on libtirpc-dev, and isn't using the glibc
> > SunRPC headers except for <rpc/netdb.h>.  libtirpc's <rpc/rpcent.h>
> > specifically avoids declaring things that are also declared in glibc's
> > <rpc/netdb.h>.
> > 
> > * ntirpc is a different port of the SunRPC code, used by nfs-ganesha.
> > 
> > * nis and nfswatch really are using the glibc SunRPC headers.
> 
> Which part of NIS?  There's a new upstream for libnsl
> <https://github.com/thkukuk/libnsl> and the NSS module
> <https://github.com/thkukuk/libnss_nis>;.  (There is a nisplus module
> as well.)

This is Debian's "nis" source package, which is a bundle of yp-tools,
ypserv, and ypbind-mt from the same upstream author.  It's unmaintained
and has lots of bug reports in Debian.

> All these use libtirpc and support IPv6 in addition to IPv4.  As far
> as I know, it is possible to build a full NIS stack without relying on
> any of the legacy glibc code.
> 
> (I don't know about nfswatch.)

The upstream for that is <https://sourceforge.net/projects/nfswatch/>. 
The current Fedora package is patched to use libtirpc.

Ben.

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom

Re: [Y2038] Trying Debian/armhf rebootstrap with time64

[Ben Hutchings]

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On Fri, 2020-03-20 at 20:54 +0000, Ben Hutchings wrote:
> On Fri, 2020-03-20 at 00:09 +0100, Florian Weimer wrote:
> > * Ben Hutchings:
> > 
> > > On Mon, 2020-03-16 at 16:02 +0100, Arnd Bergmann wrote:
> > > > On Mon, Mar 16, 2020 at 3:47 PM Rich Felker <dalias@libc.org> wrote:
> > > > 
> > > > > libtirpc is the replacement. I wasn't aware if uses libc-provided rpc
> > > > > headers (presumably only if they exist, since folks are using it fine
> > > > > on musl) but even if so I think the types will automatically update
> > > > > when time_t changes. Of course that leaves the libtirpc ABI dependent
> > > > > on which time_t is used.
> > > > 
> > > > Ok, makes sense. I suppose it just provides a header with the same
> > > > name then.
> > > 
> > > * nfs-utils build-depends on libtirpc-dev, and isn't using the glibc
> > > SunRPC headers except for <rpc/netdb.h>.  libtirpc's <rpc/rpcent.h>
> > > specifically avoids declaring things that are also declared in glibc's
> > > <rpc/netdb.h>.
> > > 
> > > * ntirpc is a different port of the SunRPC code, used by nfs-ganesha.
> > > 
> > > * nis and nfswatch really are using the glibc SunRPC headers.
> > 
> > Which part of NIS?  There's a new upstream for libnsl
> > <https://github.com/thkukuk/libnsl> and the NSS module
> > <https://github.com/thkukuk/libnss_nis>;;.  (There is a nisplus module
> > as well.)
> 
> This is Debian's "nis" source package, which is a bundle of yp-tools,
> ypserv, and ypbind-mt from the same upstream author.  It's unmaintained
> and has lots of bug reports in Debian.

I looked further at this.  The Debian package is using 2011 versions of
all these tools while the latest versions do use libtirpc.

> > All these use libtirpc and support IPv6 in addition to IPv4.  As far
> > as I know, it is possible to build a full NIS stack without relying on
> > any of the legacy glibc code.
> > 
> > (I don't know about nfswatch.)
> 
> The upstream for that is <https://sourceforge.net/projects/nfswatch/>;. 
> The current Fedora package is patched to use libtirpc.

I opened Debian bug #954380 to request making that change.

Ben.

-- 
Ben Hutchings
Kids!  Bringing about Armageddon can be dangerous.  Do not attempt it
in your own home. - Terry Pratchett and Neil Gaiman, `Good Omens'


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Re: Trying Debian/armhf rebootstrap with time64

[Steve McIntyre]

Hey Arnd,

Catching up on this thread a little late, sorry... :-/

On Wed, Mar 11, 2020 at 01:52:00PM +0100, Arnd Bergmann wrote:
>As discussed before, I tried using the rebootstrap tool [1] to see what
>problems come up once the entire distro gets rebuilt.  Based on Lukasz'
>recommendation, I tried the 'y2038_edge' branch with his experimental
>glibc  patches [2], using commit c2de7ee9461 dated 2020-02-17.
>
>Here is a rough summary of what I tried, what worked, and what problems
>I ran into:
>
>* Building a Debian package from this was fairly straightforward, using
>  the 2.31 branch in the package git repository[3] after replacing the
>  debian/patches/git-updates.diff file with one generated from [2] and
>  disabling the hurd patches because of conflicts.
>
>* After installing the modified x86 glibc package, I ran into a runtime
>  bug in [4], which needs to pass AT_FDCWD instead of 0 to avoid
>  ENOTDIR errors.
>
>* Bootstrapping a regular time32 Debian armhf with this libc took me
>  a few days to get right, but that was mostly for getting familiar
>  with rebootstrap and running into known issues unrelated to time64
>  or the glibc changes.

Cool!

<snip glibc questions>

>* There is an open question regarding the name of the Debian
>  architecture. For my experiments, I kept using the 'armhf' name
>  unmodified, though there seems to be a general feeling that using a
>  different name would be required to address the broad incompatibilities
>  between time32 and time64 versions of all the libraries in the
>  distro. Gradually changing them won't work because of the timeline and
>  the number of affected libraries. However, the new name of the distro
>  also implies having a distinct target triplet, which must then be known
>  by glibc along with everything else using config.guess/config.sub. I
>  expect this topic to require a lot more discussion.

ACK. I'm about to prod on this again.

>* Continuing with the rebootstrap build despite the known glibc issues
>  and the open question on the architecture name went surprisingly
>  well, only two out of the 152 source packages I built had
>  compile-time problems:
>
>  - building the final gcc failed in libsanitizer, which has
>    compile-time checks to ensure some libc data structures have the
>    expected layout. It noticed that 'struct timeb' and 'struct dirent'
>    are different based on _TIME_BITS and _FILE_OFFSET_BITS. I disabled
>    the checks to be able to continue. To this properly, the library
>    has to learn about the new data structures as well. I opened a
>    bug report against the library[7].
>
>  - libpreludecpp12 failed to build because of checks for changes
>    in the exported functions, which are different with time64.
>    I disabled the checks. Once we have agreed on a new debian
>    architecture name, the symbols can be made arch specific.

Yup.

>* After everything was built, I tried installing the packages into
>  a chroot with qemu-debootstrap, which failed because I had
>  configured the glibc to assume it's running on a new kernel
>  while the qemu-user binary I had lacks the new syscalls.
>  I believe this is fixed in upstream qemu, but did not try that.
>
>* Trying to install again I used a clean debian-arm64 installation
>  running in qemu-system-aarch64, and attempted installing the
>  armhf packages using a regular debootstrap, running the 32-bit
>  binaries in compat mode of a recent arm64 kernel. This partially
>  worked and I could chroot into the system and use a shell, but
>  ultimately the debootstrap did not complete because of errors.
>  I saw that 'tar' had failed because of the stat() glibc ABI mismatch
>  breaking its private gnulib fdutimens() implementation, and this is
>  where I gave up.

Nod. :-/ I think it's time that somebody else picked up from you here.

>I have spent more time on this now than I had planned, and don't expect
>to do further work on it anytime soon, but I hope my summary is useful
>to others that are going to need this later.  I can obviously share
>my patches and build artifacts if anyone needs them. There are two
>additional approaches that would likely get a Debian bootstrap further,
>but that I have not tried as they were previously dismissed:
>
>* Adding a time64 armhf as a separate (incompatible) target in glibc
>  that defines __TIMESIZE==64 and a 64-bit __time_t would avoid
>  most of the remaining ABI issues and put armhf-time64 in the same
>  category as riscv32 and arc, but this idea was so far rejected by the
>  glibc maintainers. Depending on how hard this turns out to be,
>  it could be used to get to the point of self-hosting though, and
>  help find time64 related bugs in the rest of the distro.

OK. I'm thinking it's probably not worth it?

>* Doing the bootstrap using a musleabihf target instead of gnueabihf
>  would avoid the current issues internal to glibc-y2038, but instead
>  lead to new problems with packages that do not currently work with
>  musl. Adelie Linux has shown that it's already possible to build
>  a useful distro using musl and time64[8], and this would
>  sidestep the question of the target triplet. While it would also
>  help find and fix additional bugs in packages, and make an
>  interesting unoffical Debian target, I don't see it replacing
>  the existing armhf port any time soon.

Ditto.

Thanks for the great summary of what you've been working on!

-- 
Steve McIntyre, Cambridge, UK.                                steve@einval.com
"When C++ is your hammer, everything looks like a thumb." -- Steven M. Haflich

Re: Trying Debian/armhf rebootstrap with time64

[Arnd Bergmann]

On Mon, Mar 23, 2020 at 7:21 PM Steve McIntyre <steve@einval.com> wrote:
> On Wed, Mar 11, 2020 at 01:52:00PM +0100, Arnd Bergmann wrote:
> >* Adding a time64 armhf as a separate (incompatible) target in glibc
> >  that defines __TIMESIZE==64 and a 64-bit __time_t would avoid
> >  most of the remaining ABI issues and put armhf-time64 in the same
> >  category as riscv32 and arc, but this idea was so far rejected by the
> >  glibc maintainers. Depending on how hard this turns out to be,
> >  it could be used to get to the point of self-hosting though, and
> >  help find time64 related bugs in the rest of the distro.
>
> OK. I'm thinking it's probably not worth it?

This depends on the timeline of Lukasz' work. My feeling is that there is still
quite a bit to be done before it's worth trying the Debian bootstrap again.

If you or someone else wants to continue where I stopped with the Debian
rebuilding without waiting for the complete glibc port, adding a new armhf
target to glibc on top of the current glibc-y2038 tree is probably a quicker
way to get something that builds and boots. I don't know how much work
exactly there would be for this approach, but my feeling is that it's not that
much after looking at the kind of problems I ran into, and at the state of
the riscv32 port that uses the same approach.

        Arnd

Re: Trying Debian/armhf rebootstrap with time64

[Lukasz Majewski]

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Dear Community,

> On Mon, Mar 23, 2020 at 7:21 PM Steve McIntyre <steve@einval.com>
> wrote:
> > On Wed, Mar 11, 2020 at 01:52:00PM +0100, Arnd Bergmann wrote:  
> > >* Adding a time64 armhf as a separate (incompatible) target in
> > >glibc
> > >  that defines __TIMESIZE==64 and a 64-bit __time_t would avoid
> > >  most of the remaining ABI issues and put armhf-time64 in the same
> > >  category as riscv32 and arc, but this idea was so far rejected
> > > by the glibc maintainers. Depending on how hard this turns out to
> > > be, it could be used to get to the point of self-hosting though,
> > > and help find time64 related bugs in the rest of the distro.  
> >
> > OK. I'm thinking it's probably not worth it?  
> 
> This depends on the timeline of Lukasz' work. My feeling is that
> there is still quite a bit to be done before it's worth trying the
> Debian bootstrap again.

The development is moving forward with help of RV32 (Alistair) and ARC
developers. Community helps with reviewing as much as they can.
Current status can be viewed here:
https://github.com/lmajewski/y2038_glibc/commit/2af7f31548625ac0a19c98a505987f4d92c51d56


I've also already addressed some comments from Arnd and updated the
y2038_edge branch:
https://github.com/lmajewski/y2038_glibc/commits/y2038_edge

Some other comments still wait for being addressed.

> 
> If you or someone else wants to continue where I stopped with the
> Debian rebuilding without waiting for the complete glibc port, adding
> a new armhf target to glibc on top of the current glibc-y2038 tree is
> probably a quicker way to get something that builds and boots. I
> don't know how much work exactly there would be for this approach,
> but my feeling is that it's not that much after looking at the kind
> of problems I ran into, and at the state of the riscv32 port that
> uses the same approach.

As we are not in a big hurry for Y2038, IMHO it would be better to help
with reviewing and developing the mainline glibc to be Y2038 safe.

> 
>         Arnd


Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de

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