[ Also posted to debian-arm; not cross-posted to avoid subscription
complaints... ]
Hi folks,
We're currently carrying patches in glibc in Debian (and Ubuntu) that
I wrote which are used to work out whether an ELF binary is hard-float
or soft-float. We're using these to allow us to do the right thing on
a multi-arch system, which is to pick a consistent set of binaries
(programs and libraries) at runtime; if you try to mix binaries using
different ABIs, you're prone to all kinds of weird and wonderful
results but generally badness occurs.
Upstream glibc have generally not been welcoming of these patches, and
I understand this; the approach taken (reading ARM-specific build
attributes) is far from clean and doesn't fit well in the design of
ld.so in particular. So, I've been looking into alternative methods
for achieving the goal of identifying ABI. After a couple of false
starts and discussion with some of the helpful toolchain and ABI folks
in ARM, I think we have a solution that will work well in the long
term. I just wish we'd thought about this *way* back when we first
started the armhf port, as it would have been much easier to work on
and standardise this back then. Modulo availability of time machines,
there's not much we can do on that front... :-)
What I'm proposing is to use two new values in the OSABI field in the
ELF header:
#define ELFOSABI_LINUX_ARM_AEABI_SF 65
#define ELFOSABI_LINUX_ARM_AEABI_HF 66
and use these values in the future for soft- and hard-float binaries
so that can unambiguously identify them.
There's already precedent for binaries using different values in this
field, with support in glibc for parsing and understanding
them. Adding more possible values is quite easy, assuming that the
maintainers are amenable. I'm about to post a similar message there.
I have a plan of attack for how to make a staged switch over,
deliberately to minimise any potential compatibility problems. See the
attached doc for that. It's deliberately not very specific in terms of
timeline, as that's something I'm hoping to get feedback
about. Comments very welcome; please point out if you think there are
problems with this approach, or if there are any more implementations
of toolchain / linker that will need to be addressed.
Cheers,
--
Steve McIntyre steve.mcintyre(a)linaro.org
<http://www.linaro.org/> Linaro.org | Open source software for ARM SoCs
For reference, if you see link time errors about a missing
'__dso_handle' symbol when building Android, then check if you're
using any global class instances in your multimedia libraries.
Each shared library has a __dso_handle symbol which is filled in on
load by the dynamic loader. Global class instances use this unique
value to make sure the destructor is called when the library is
unloaded. The symbol itself is defined in crtbegin_so.o, but the
multimedia rules forbid using this for an unknown reason. Either
create your global instances in a different way or change the
multimedia rules :)
-- Michael
== Progress ==
* Fixed PR54051
* Improved neon intrinsics testsuite. While still not an execution
based testsuite atleast we get compile time tests that are sensible C.
Exposed issues - wrote patches.
that improve vabal , vaba intrinsics. Fix an issue with costs,
fixed an issue with splitters for large mode moves for Neon with
hardfp port etc.
* Some upstream patch and bug review.
* Fixed a minor testism for vld1q_s64 tests.
== Plans ==
* Write a patch to check md5sums between local tarball and uploaded
tarball in the release script.
* Look at auto-inc-dec patches more and investigate benchmark results.
* Submit intrinsics work upstream and sheperd it through.
* Finish looking at PR53664 and clean up testsuite further.
* Follow-up on my intrinsics patches upstream.
== Absences ==
* 17th Sept - 5th Oct - Vacation approved.
== GCC ==
* Checked in fix fix for incorrect pool placement with -O0
by splitting all insns in machine-dependent reorg.
* Created blueprint to investigate -funroll-loops and
-fvariable-expansion-in-unroller.
* Took over patch to change vector alignment to 8 from
Richard; reworked according to review comments; found
and fixed two vectorizer bugs triggered by the change;
submitted for mainline approval.
* Continued investigation of reload bug reported by ARM.
Posted potential fix to gcc-patches for discussion.
== GDB ==
* Worked on fixing HW breakpoint/watchpoint regressions.
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
--
Dr. Ulrich Weigand | Phone: +49-7031/16-3727
STSM, GNU compiler and toolchain for Linux on System z and Cell/B.E.
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter | Geschäftsführung: Dirk
Wittkopp
Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht
Stuttgart, HRB 243294
Current Milestones:
|| || Planned || Estimate || Actual ||
||cp15-rework || 2012-01-06 || 2012-06-23 || 2012-06-24 ||
||a15-lpae-support || 2012-07-13 || 2012-07-20 || 2012-07-20 ||
||clean-up-kvm-patches || || || ||
||track-kvm-abi-changes || || || ||
||fake-trustzone || || || ||
Overall KVM plan for 'do by end August': QEMU parts of this are a mix
of clean-up-kvm-patches and track-kvm-abi-changes blueprints, mostly.
http://cards.linaro.org/browse/CARD-167
== clean-up-kvm-patches ==
* sent patch series to try to clean up some QEMU kvm x86isms
that block cleanup of some of the ARM KVM support code;
dealt with review comments and sent v2
== other ==
* started on cleaning up the QEMU benchmarking setup so we
can put it on a server machine somewhere
* fixed a crash in the QEMU ARMv7M models which was introduced
by one of my earlier GIC/NVIC refactoring series
* upstream review/maintainer duties
KVM blueprint progress tracker:
http://apus.seabright.co.nz/helpers/backlog?group_by=topic&colour_by=state&…
-- PMM
FYI GCC trunk r189808 fails to build with a bootstrap comparison error:
Comparing stages 2 and 3
warning: gcc/cc1-checksum.o differs
warning: gcc/cc1plus-checksum.o differs
warning: gcc/cc1obj-checksum.o differs
warning: gcc/cc1objplus-checksum.o differs
Bootstrap comparison failure!
arm-linux-gnueabi/libgcc/unwind-arm.o differs
arm-linux-gnueabi/libgcc/unwind-arm_s.o differs
189575 was fine on hard float. 189745 is fine on softfp.
-- Michael
---------- Forwarded message ----------
From: Linaro Toolchain Builder <michael.hope+cbuild(a)linaro.org>
Date: 25 July 2012 15:59
Subject: [cbuild] gcc-4.8~svn189808 armv7l failed
To: "michael.hope+notify(a)linaro.org" <michael.hope+notify(a)linaro.org>
ursa3 finished running job gcc-4.8~svn189808 on
armv7l-precise-cbuild348-ursa3-cortexa9hfr1.
The results are here:
http://builds.linaro.org/toolchain/gcc-4.8~svn189808
This email is sent from a cbuild (https://launchpad.net/cbuild) based
bot which is administered by Michael Hope <michael.hope(a)linaro.org>.
Hello Ramana,
For your PGO list:
* please note that I've been working on PGO for switch code, and also
for chains of if-statements with a common condition variable (with Tom
de Vries)
* turning conditional execution off will not make a difference, your
profile information will be exactly the same. Profile instrumentation
happens very early in the pipe line (on purpose, PGO is more
accurately "coverage guided optimization", not profiling in the
prof/gprof/oprofile sense). And the parts of the CFG that have profile
instrumentation cannot be if-converted anyway.
* you can use the script "analyze_brprob" in contrib/ to measure the
accuracy of the branch predictors. The script needs some TLC, fixing
it is on my TODO list but let me know if linaro folks are going to
take care of that. You'll find that the predictors are heavily tuned
towards the original Opteron, I'm not aware of much tuning for other
architectures.
* The heuristics for profile-guided optimizations are also not tuned
for arm. In the past we found that some params have more influence
than others (the TRACER* parameters for example).
Hope this helps,
What do you mean with "Only conditionalise those parts that benefit"?
Ciao!
Steven
