I have noticed gcc has a preference for generating UXTB instructions
when an AND with #255 would do the same thing. This is bad, because
on A9 UXTB has two cycles latency compared to one cycle for AND. On
A8 both instructions have one cycle latency.
--
Mans Rullgard / mru
== GCC ==
* Checked in patch to change vector alignment to 8
to GCC mainline.
* Started investigating benchmark regressions with
Linaro GCC 4.7 backport of vector alignment patch.
== GDB ==
* Checked in patch to fix hardware breakpoints on
non-4-byte aligned (Thumb) instructions.
* Checked in patch to properly report unsupported
watchpoint address/length combinations in gdbserver.
* Checked in patch to fix regression accessing /proc
files on older Linux kernels.
* Checked in 5 more patches to fix miscellaneous
test suite regressions.
* Re-tested GDB 7.5 pre-release on multiple platforms.
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
[ 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
