- linaro-toolchain - lists.linaro.org

by Michael Hope

Hi there. The sprint is just around the corner and it's a good time to think about how we can make best use of the week. I've put some topics up at: https://wiki.linaro.org/Events/2011-01-LinaroSprint/ToolChainWG Please feel free to add to it. Have a think about anything that's easier to do while everyone is in the same room - things like discussions, kicking off some work, a bit of pair programming on a problem, or anything that overlaps with another group or Ubuntu. -- Michael

14 years, 11 months

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[ACTIVITY] report week 50

by Peter Maydell

RAG: Red: Amber: Green: Milestones: | Planned | Estimate | Actual | finish virtio-system | 2010-08-27 | postponed | | get valgrind into linaro PPA | 2010-09-15 | 2010-09-28 | 2010-09-28 | complete a qemu-maemo update | 2010-09-24 | 2010-09-22 | 2010-09-22 | finish testing PCI patches | 2010-10-01 | 2010-10-22 | 2010-10-18 | Progress: * merge-correctness-fixes: ** Submitted patchset upstream to fix NaN propagation to follow ARM ARM rules rather than x87 semantics: http://patchwork.ozlabs.org/patch/75742/ http://patchwork.ozlabs.org/patch/75743/ * maintain-beagle-models: ** Finished implementation of the OMAP NAND prefetch/postwrite engine including its DMA support. Patches submitted to the qemu-maemo upstream tree and merged by Juha: http://meego.gitorious.org/qemu-maemo/qemu/merge_requests/1 ** Fixed the (cosmetic) bug https://bugs.launchpad.net/qemu-maemo/+bug/622408 where we were complaining about "Unknown CMD52" when Linux probed for the presence of SDIO cards. Fix merged into qemu-maemo: http://meego.gitorious.org/qemu-maemo/qemu/merge_requests/2 * qemu-continuous-integration: ** Discussion with Loic about setting up jobs on his Hudson instance for testing qemu against snapshots/hwpacks. * packageselection-arm-n-more-stable-vm-solution-for-arm ** Discussion about Ubuntu moving to using a qemu-maemo based qemu for ARM purposes. The Ubuntu blueprint is https://blueprints.launchpad.net/ubuntu/+spec/packageselection-arm-n-more-s… We need to come to agreement about what parts of this are going to be done by variously Linaro toolchain, Linaro foundations and Ubuntu. ** I'm going through doing another rebase-and-package of the Linaro qemu, and finishing off writing up the notes on the process: https://wiki.linaro.org/WorkingGroups/ToolChain/QemuReleaseProcess Meetings: toolchain, pdsw-tools, pdsw-tools xmas lunch :-) Issues: * a number of qemu patches in progress are logjammed behind the outstanding git pull request * the dbgsym debug packages for linaro kernels seem to have vanished: https://bugs.launchpad.net/linaro-images/+bug/691192 Absences: (complete to end of 2010) Fri 17 Dec - Tue 4 Jan inclusive. 2011: Dallas Linaro sprint 9-15 Jan. Holiday 22 Apr - 2 May.

14 years, 11 months

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[ACTIVITY] weekly status

by Ken Werner

Hi, * I've spent some time for testing the patches that allow the GCC trunk to bootstrap again on ARM and posted the results to gcc-testresults * finally tested and posted the patch that optimizes the __sync_* builtins (#681138) on gcc-patches * investigated on the state of the crash utility on ARM (or rather its prerequisites like kexec) https://wiki.linaro.org/KenWerner/Sandbox/crash-utility * I'm on holiday now :) Regards Ken

14 years, 11 months

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Re: RFC: -mimplicit-it and GCC upstream

by Dave Martin

Hi, On Wed, Dec 15, 2010 at 1:44 AM, Michael Hope <michael.hope(a)linaro.org> wrote: > On Wed, Dec 15, 2010 at 1:05 PM, Steve Langasek > <steve.langasek(a)linaro.org> wrote: >> Hi Michael, >> >> On Wed, Dec 15, 2010 at 09:29:38AM +1300, Michael Hope wrote: >>> Hi Steve. I'd like to hand the rest of this over to you if that's OK. >> >> Yep, we can take it from here. To be clear, is this an additional change >> above and beyond what Matthias reports is currently in Ubuntu gcc >> (http://lists.linaro.org/pipermail/linaro-toolchain/2010-November/000441.html), >> and if so, in what version of Linaro GCC is it going to become effective? >> Do we have documentation of what the relevant failure modes caused by this >> change *look* like, so that we can at least be triaging them appropriately >> until there's some documentation on how to fix the resulting bugs? > > There will be many failures in many packages. The problem is when you > use conditional suffixes on instructions: previously the compiler > would insert an implicit instruction before that; now we have to be > explicit. > > The failures are easy to diagnose and fix. The build will fail with a > message from the assembler along the lines of 'xxx instruction outside > an IT block'. The fix is to find the inline assembly code, insert the > appropriate IT instruction, and re-build. The assembler will validate > the IT instruction against the following conditional instructions so > the change is quite safe. Did someone manage to find out which versions of binutils can silently accept the IT instructions when assembling for ARM? This affects what advice we should give on how to avoid breaking upstream with our additions. The safest approach is #ifdefs, but it will be better for maintenance if we can avoid this, since it will render the code very messy. Cheers ---Dave

14 years, 12 months

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Blueprint changes

by Michael Hope

Hi there. Some of the tr-* blueprints had work items in them and this was interfering with the tools that the PM guys use. I've created new engineering blueprints, pulled the work items across into them, and added the new engineering blueprint as a dependency of the old TR. Sorry for the blueprint spam. In most cases the new blueprint has the same name and subject as the TR one, such as the TR: https://blueprints.launchpad.net/linaro/+spec/tr-toolchain-4.5-in-distros which is backed by the engineering blueprint: https://blueprints.launchpad.net/gcc-linaro/+spec/4.5-in-distros -- Michael

14 years, 12 months

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RFC: -mimplicit-it and GCC upstream

by Dave Martin

Hi Richard, Recapping on this earlier conversation: http://lists.linaro.org/pipermail/linaro-toolchain/2010-July/000030.html http://lists.linaro.org/pipermail/linaro-toolchain/2010-July/000035.html Is it worth another attempt to make a case to upstream for supporting passing -mimplicit-it=thumb by default to gas? According to my understanding of this issue, my argument would go as follows: * gcc currently estimates the size of asm blocks, rather than determining the size accurately. * gcc cannot guarantee the right answer for asm block size when asm blocks contain directives etc., however use of directives in asm blocks is widespread * gcc cannot guarantee the right answer for asm block size in Thumb-2. gcc conservatively overestimates the size by assuming that each statement of the asm block expands to 4 bytes. * All of Ubuntu lucid and maverick has been built with -mimplicit-it=thumb passwd by default, with no known build or runtime failures arising from this (so size issues aside, we have confidence that the resulting code generation is sound) * -mimplicit-it=thumb -mthumb makes the asm block size estimation unsafe: the asm block can exceed the estimated size even in the absence of directives, which may lead to fixup range errors during assembly. * Following the principles already established for Thumb-2 in general the estimation can be made safe (or, as safe as the established Thumb-2 behaviour) by raising the assumed maximum statement expansion size for asm blocks to 6 bytes, since -mimplicit-it will add as most a single (16-bit) IT instruction to each statement. * The vast majority of all asm blocks are small (< 20 instructions, say), so the overall overestimate in sizes will generally be modest for any given compilation unit. * -mimplicit-it is already _required_ by the Linux kernel and possible other projects. ...so... * With -mimplicit-it=thumb and a 6-byte asm block statement expansion size estimate, we have toolchain behaviour which is as reliable, and as correct, as it is in upstream at present. * Layout of data in the compiler output will be more optimal in some cases, and less optimal in other cases, compared with the the current Thumb-2 behaviour, due to differing asm block size estimates. The exact behaviour will depend on the distribution of conditional instructions within asm blocks. * Taken over a whole compilation unit, the total code size overestimate (and therefore the impact on object layout) will normally be modest, due to the small typical size of asm blocks. * Behaviour for -marm will not be impacted at all. If gcc currently estimated asm block code size accurately, then I could understand upstream's objection; but as it stands it seems to me we wouldn't be making anything worse in practice with the proposed change; and there is no compatibility impact (other than positive impact). Of course, I may have some wrong assumptions here, or there may be some background I'm not aware of... Comments? Cheers ---Dave

14 years, 12 months

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[ACTIVITY] December 6th-12th

by Julian Brown

== Linaro GCC == * Finish testing for big-endian/quad-word patch on mainline, and send upstream. Not yet reviewed by an ARM maintainer, but Joseph suggested tweaking DejaGnu's target-supports to better reflect the new capabilities of the vectorizer in big-endian mode. I've not looked into that yet. * Started looking at improving element/structure load/store intrinsics. Made it so that the structs used for loads/stores are created in the backend so that the types can be used directly by the builtins, but discovered that the front-end/middle-end would not play along with that plan as they are. Thought about ways to fix that. * Some time spent on other CodeSourcery stuff.

14 years, 12 months

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Linaro GCC 4.4 and 4.5 2010-12 released

by Michael Hope

The Linaro Toolchain Working Group is pleased to announce the release of both Linaro GCC 4.4 and Linaro GCC 4.5. Linaro GCC 4.5 is the fifth release in the 4.5 series. Based off the latest GCC 4.5.1+svn167157, it includes many ARM-focused performance improvements and bug fixes. Linaro GCC 4.4 is the fifth release in the 4.4 series. Based off the latest GCC 4.4.5, it is a maintenance release that fixes one problem found through use. Interesting changes include: * A new performance focused extension elimination pass * Speed and size improvements when loading constants * Performance improvements on compound conditionals * A range of correctness improvements The source tarballs are available from: https://launchpad.net/gcc-linaro/+milestone/4.5-2010.12-0 and https://launchpad.net/gcc-linaro/+milestone/4.4-2010.12-0 Downloads are available from the Linaro GCC page on Launchpad: https://launchpad.net/gcc-linaro No changes have been committed to Linaro GDB 7.2 this month. -- Michael

14 years, 12 months

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[ACTIVITY] 6th - 10th December

by Andrew Stubbs

* Linaro GCC 4.4/4.5 Merged the latest CS patches and Linaro merge requests into Linaro GCC (4.4 and 4.5). Ran regression tests. Yao's patch failed so I backed it out, and made the release tarballs. Uploaded the releases to Michael Hope for release. lp:686381: luatex fails to build with gcc-4.5 Fired off a test build to reproduce the problem. Will come back to this next week. * GCC 4.6/4.7 Posted my various queued patches up to gcc-patches(a)gcc.gnu.org for review. Looked at the state of the GCC 4.6 upstream build. There are currently two problems: 1. libquadmath must be disabled in a cross-build for the bootstrap phases. 2. libstdc++ doesn't build. There is a patch for it on the mail list, but it's not applied yet. Once gcc 4.6 builds cleanly, I shall update the Launchpad 4.6 branch, and declare that the baseline for our development. We'll then have somewhere to commit and track patches awaiting GCC stage 1 development. * Other Caught up with email following my holiday. Yet again, my IGEPv2 board suffered a corrupt file system. I've now upgraded the kernel and configured it to use an NFS root. The board is now somewhat less mobile, but should work more reliably. Continued organizing the a brain-storming session for GCC optimization improvements. Organised flights and hotel for both the Linaro Sprint and CodeSourcery annual meeting in January.

14 years, 12 months

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[ACTIVITY] Dec. 06 -- Dec. 12

by Zach Welch

== Last Week == * Spent time tracking down a couple of regressions that appeared in the new ltrace release-candidate tree. Submitted a bunch of patches to fix the issues that were discovered during that process; most have been applied. * Finished writing fairly generic code for handling ARM-specific unwind tables, from lookup through decoding and dispatch. It uses a few definitions specific to libunwind, but those probably could be eliminated with more work. == This Week == * Integrate new ARM-specific bits into libunwind framework. * Rewrite part of a portability patch for ltrace and hope that those changes reflect the very last effort that will be required for that particular task. -- Zach Welch CodeSourcery zwelch(a)codesourcery.com (650) 331-3385 x743

14 years, 12 months

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Re: Neon registers in core files

by Dave Martin

On Fri, Dec 3, 2010 at 9:06 AM, Yao Qi <yao.qi(a)linaro.org> wrote: > Hi, Kernel WG, > Can recent kernel handle NEON registers in corefiles? > > Seems we've had plan for this in "Ensure full NEON debug support" in > https://wiki.linaro.org/WorkingGroups/KernelConsolidation/Specs/BSPInvestig… > Any progress on this piece of work? We want to handle NEON registers in > corefiles from GDB, which required kernel dump them in corefile first. Hmmm, actually that bullet may have ended up in the wrong place ... since it's not a BSP-specific feature. Anyway, looking at the kernel code, it looks like the VFP/NEON state is not dumped into the core file. If it makes you feel better, the state of the obsolete FPE extension registers is dumped, if used :/ My guess is that it shouldn't be hard to dump the VFP/NEON state, but GDB and the kernel need to agree on the format. Rather that trying to hack the existing register dump format in a compatible way, I suggest it's simplest if the kernel creates an extra section in the dump containing something like: .long format_version /* reserved for future expansion - must be 0 */ .long FPSID .long FPSCR .long MVFR0 /* or 0 if not present in the hardware */ .long MVFR1 /* or 0 if not present in the hardware */ .long d0 .long d1 /* ... d2-d14 ... */ .long d15 If 32 D-registers in the hardware [ .long d16 .long d17 /* ... d18-d30 ... */ .long d31 ] I believe we don't need any extra flags to indicate whether the MVFRx fields are valid, since 0 in these registers indicates the VFPv2/legacy behaviour anyway. Note that some VFPv2 implementations (such as ARM1176) do provide these registers, and where the hardware has them, the kernel can fill them in when doing the coredump. We _should_ be prepared to ignore these fields (or interpret them differently) if a vendor-specific VFP subarchitecture is specified (by (FPSID & 0x4000) == 0x4000) The number of D-registers can be deduced from the FPSID and MVFRx registers, so we don't need to record it explicitly. When MVFRx are not present, there are 16 D-registers. When MVFRx are present, and (MVFR0 & 0xF) >= 2, there are 32 (or more) D-registers This is just a sketch -- the ARM ARM is the authoritative reference on the meanings of these bitfields. Any views on this? Cheers ---Dave > > _______________________________________________ > linaro-dev mailing list > linaro-dev(a)lists.linaro.org > http://lists.linaro.org/mailman/listinfo/linaro-dev >

14 years, 12 months

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[ACTIVITY] Dec 6 - Dec 10

by Ulrich Weigand

== GCC == * Tracked down root cause of GCC mainline bootstrap failure on ARM (PR 46040 - "__DTOR_LIST__ undeclared"). == Miscellaneous == * Set up IGEP v2 board (w/ local disk, network, ...) as native GCC / GDB build environment. * Gave talk on Linaro at the "2010 Linux Community Event" at Siemens Munich (w/ Arnd Bergmann). 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

14 years, 12 months

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Invitation: TWG GCC Optimization @ Wed 2010-12-15 9am - 10am (linaro-toolchain@lists.linaro.org)

by Andrew Stubbs

You have been invited to the following event. Title: TWG GCC Optimization Discuss ideas for improving GCC optimization for ARM. Open to anybody who wants to contribute. https://wiki.linaro.org/AndrewStubbs/Sandbox/GCCoptimizations International: +44 1452 567 588 UK: 0844 493 3801 Brazil: 08008912092 China: 108007121533 India: 0008001006354 Taiwan: 00801126472 United States: 18666161738 Conference code 2634417169# When: Wed 2010-12-15 9am – 10am London Where: Conference call code 263 441 7169 Calendar: linaro-toolchain(a)lists.linaro.org Who: * andrew.stubbs(a)linaro.org - creator * Ken Werner - optional * stevenb.gcc(a)gmail.com - optional * Michael Hope - optional * David Gilbert - optional * Peter Maydell - optional * ulrich.weigand(a)de.ibm.com - optional * Yao Qi - optional * Julian Brown - optional * paul(a)codesourcery.com - optional * Ira Rosen - optional * richard.earnshaw(a)arm.com - optional * Chung-Lin Tang - optional * mark(a)codesourcery.com - optional * linaro-toolchain(a)lists.linaro.org - optional * Richard Sandiford - optional * Marcin Juszkiewicz - optional * zwelch(a)codesourcery.com - optional Your attendance is optional. Event details: https://www.google.com/calendar/event?action=VIEW&eid=aXJlc2Z2bWZmZzQ5cGQ4b… Invitation from Google Calendar: https://www.google.com/calendar/ You are receiving this courtesy email at the account linaro-toolchain(a)lists.linaro.org because you are an attendee of this event. To stop receiving future notifications for this event, decline this event. Alternatively you can sign up for a Google account at https://www.google.com/calendar/ and control your notification settings for your entire calendar.

14 years, 12 months

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[ACTIVITY] Dec.6th -- Dec.12th

by Chung-Lin Tang

== GCC related == * PR44557, Thumb-1 ICE: found two small needed corrections in the ARM backend to fix this. Sent patch upstream. * LP:641397/PR46888: bitfield insert optimization. Posted patch along with Andrew Stubbs' CSE patch upstream. The two-patch situation seemed to stir some discussion :) It seems both patches were deemed okay, though it would be better if there was some testcase that passed through unhandled by Andrew's CSE patch, but processed by my combine fix later in the pass pipeline. Both patches queued at GCC bugzilla page, to be handled in the next stage1. * LP:687406/PR46865, -save-temps creating different code. Analyzed problem, though slow to send fix upstream. Had some discussion on the list on how the fix should be like. * PR46667, section type conflicts. Tested and sent mail to gcc-patches. Jan Hubicka picked it up and pinged for an approval again. Hope this get resolved soon. * PR45416, ARM code regression. ARM considerations are mostly okay, main issue remaining is how to solve the x86 regression. The current expand code does a full DImode shift just to obtain a single bit, might be point of improvement to solve this. * LP:685534, ftbfs with gcc-linaro 4.5 on amd64. Found to be another erroneous inline asm case. Fixed and updated on LP. == This week == * More upstream and Linaro GCC issues. * Start dealing with January travel. * Think more about larger (Linaro) GCC optimization projects.

14 years, 12 months

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[ACTIVITY] Dec 6th -- Dec 12th

by Yao Qi

== Linaro GDB == * LP:616000 Handle -fstack-protector prologue code Understand how frame affect expression validation in GDB. Improve i386 prologue parsing to handle 'and/add' sequence. Revise i386 prologue parsing for stack protector. Patch is not submitted since still lack of i386 prologue knowledge, and not very confident on that patch. Understand prologue-value used in ARM prologue parsing and relationship of symbol and frame in GDB. Make ARM prologue parsing understands stack protector code by identify the code sequence. Improve the patch by supporting ARM mode and ARMv5T, in order to make this patch accepted by upstreams. * LP:615972 gdb.base/gcore.exp failure. The failure is about "corefile restored general registers", which is not related to NEON register support in corefile. It is caused by inconsistent register types and names between tdesc and arm. The cause of this failure is found, but upstreams reviewer doesn't agree on one of my fix. As he suggested, arm-core.xml is modified to add "type=XXX", but get some errors when regenerate arm-with-iwmmxt.c. Filed GDB PR 12308. == GCC == * register rename improvements (LP:633243) Finally, got both middle-end part and ARM part approved. Committed to upstreams mainline. Some benchmarks in EEMBC shows 0.1%~0.2% code size reduction. == This Week == * Ping my GDB patches. * Fix GDB PR 12308, which blocks my fix for LP:615972. * Backport my approved patches to Linaro GDB if any. Fix other GDB bugs. * Pass one GCC patch in my queue to review, if I have extra time. == Vacation == Take vacation on Dec 30th and 31st. Travel to ChengDu, and back on 3rd Jan (It is public holiday in China). Back to work on 4th Jan. -- Yao (齐尧)

14 years, 12 months

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[ACTIVITY] Weekly status

by Richard Sandiford

== This week == * Away Monday and Tuesday. * Very little the rest of the week due to other IBM commitments. I've just finished the main part of that work, so all being well, it should only need a bit of nannying next week. Most of the week should be Linaro. * Started trying to reproduce #641126, but realised that I'd need to set myself up for general Ubuntu cross package building first. Started to look at what's involved. == Next week == * Get stuck into #641126. * More STT_GNU_IFUNC and vectors. Richard

14 years, 12 months

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[ACTIVITY] report week 49

by Peter Maydell

RAG: Red: Amber: Green: Milestones: | Planned | Estimate | Actual | finish virtio-system | 2010-08-27 | postponed | | get valgrind into linaro PPA | 2010-09-15 | 2010-09-28 | 2010-09-28 | complete a qemu-maemo update | 2010-09-24 | 2010-09-22 | 2010-09-22 | finish testing PCI patches | 2010-10-01 | 2010-10-22 | 2010-10-18 | Progress: * merge-correctness-fixes: ** I have sent out an updated ARM fixes pull request, all of whose components have been Reviewed-by: Nathan Froyd; I expect this to be merged shortly. ** vqshl(reg) patch posted to list; I have an update which also addresses vqshl{,u}(imm) which I'll send out as v2 once the first part has been reviewed. ** reviewed and retransmitted Wolfgang's semihosting commandline patches since he is having trouble sending unmangled mail to the list ** went through the monster qemu-maemo commit "Lots of ARM TCG changes" http://meego.gitorious.org/qemu-maemo/qemu/commit/3f17d4e1cb identifying what fixes it includes ** started looking at a VRSQRTS patch. This uncovered a number of qemu issues: NaN propagation is wrong, flush-to-zero handling is only flushing output denormals, not input denormals, and we don't handle the Neon "standard FPSCR value" but always use the real FPSCR. I have some preliminary patches for at least some of this, but since they affect a number of the same bits of code that are touched by existing not-yet-committed patches I'm waiting for those to be committed first. * verify-emulation: ** wrote a README for risu and made it public at http://git.linaro.org/gitweb?p=people/pmaydell/risu.git;a=summary * maintain-beagle-models: ** the ubuntu maverick netbook image doesn't boot on qemu because it uses the OMAP NAND prefetch/DMA, which isn't modelled https://bugs.launchpad.net/qemu-maemo/+bug/645311 I've started on this and am perhaps halfway through (basic prefetch code implemented, but DMA and debugging still to go) * other: ** took part in an OBS mini-sprint where we were walked through how the OBS buildsystem works and can be used to do test rebuilds of Meego with new versions of the toolchain. Meetings: toolchain, pdsw-tools Plans: * finish omap NAND prefetch engine work * make sure ARM changes get committed to qemu... Absences: (complete to end of 2010) Fri 17 Dec - Tue 4 Jan inclusive. 2011: Dallas Linaro sprint 9-15 Jan. Holiday 22 Apr - 2 May.

15 years

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[ACTIVITY] weekly status

by Ken Werner

Hi, * created custom kernel deb packages from the linaro-linux tree in order to * test the various ftrace tracers and profilers available on ARM * results at: https://wiki.linaro.org/KenWerner/Sandbox/ftrace * started to look into crash (kexec, kdump) but wasn't able to generate a kernel dump yet Regards Ken

15 years

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Perfromance Test Results using gcc-linaro-4.5-2010.11-1

by Prashanth S

Dear All Our team in Samsung collected some performance metrics for the following 3 GCC cross compilers 1.. Gentoo Complier(part of Chrome OS Build Environment) 2.. GCC 4.4.1 (Code Sourcery). 3.. Linaro (gcc-linaro-4.5-2010.11-1) Flags used to Build Linaro Tool chain used Michael Hope Script .Just modified "GCCFLAGS = --with-mode=thumb --with-arch=armv7-a --with-float=softfp --with-fpu=neon --with-fpu=vfpv3-d16" a.. Using the above three tool chains we compiled the kernel of Chrome OS and did Coremark Performance test.(With same optimisation flag mentioned in the attachment) b.. Test Environment for all the three are the same. My Questions 1.. Is there any build options that I am missing while I am building the Cross Compiler? 2.. Else is this performance degradation is a know issue and is the tool chain group working on it?.(If so whom to contact?) Any Pointers from you would be of great help to me. If you need any further details also do ping me Regards Prashanth S

15 years

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GCC Optimization Brain Storming Session

by Andrew Stubbs

Hi All, As we discussed on Monday, I think it might be helpful to get a number of knowledgeable people together on a call to discuss GCC optimization opportunities. So, I'd like to get some idea of who would like to attend, and we'll try to find a slot we can all make. I'm on vacation next week, so I expect it'll be in two or three week's time. Before we get there, I'd like to have a list of ideas to discuss. Partly so that we don't forget anything, and partly so that people can have a think about them before the day. I'm really looking for bigger picture stuff, rather than individual poor code generation bugs. So here's a few to kick off: * Costs tuning. - GCC 4.6 has a new costs model, but are we making full use of it? - What about optimizing for size? - Do the optimizers take any notice? [1] * Instruction set coverage. - Are there any ARM/Thumb2 instructions that we are not taking advantage of? [2] - Do we test that we use the instructions we do have? [3] * Constant pools - it might be a very handy space optimization to have small functions share one constant pool, but the way the passes work one function at a time makes this hard. (LP:625233) * NEON - There's already a lot of work going on here, and I don't want it to hog all our time, but it might be worth touching on. What else? I'm not the most experienced person with GCC internals, and I'm relatively new to the ARM specific parts of those, so somebody else must be able to come up with something far more exciting! So, please, get brain-storming! Andrew [1] We discovered recently that combine is happy to take two insns and combine them into a pattern that matches a splitter that then explodes into three insns (partly due to being no longer able to generate pseudo-registers). [2] For example, I just wrote a patch to add addw and subw support (not yet submitted). [3] LP:643479 is an example of a case where we don't.

15 years

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[ACTIVITY] 2010-12-09

by David Gilbert

Mostly more working with libffi; swapping some ideas back and forwards with Marcus Shawcroft and it looks like we have a good way forward. Got an armhf chroot going, libffi built. Got a testcase failing as expected. Trying to look at other processors ABIs to understand why varargs works for anyone else. Cut through one layer of red tape; can now do the next level of comparison in the string routine work. Started looking at SPEC; hit problems with network stability on VExpress (turns out to be bug 673820) long long weekend; short weeks=2; Back in on Tuesday. Dave

15 years

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Silverbell

by David Gilbert

Hi, Those of you use silverbell may be glad to know it's back up. Be a little careful, if you shovel large amounts of stuff over it's network the network tends to disappear. (Not sure if this is hardware or driver) Dave

15 years

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Hard float chroot

by David Gilbert

Hi, As mentioned on the standup, I just got an armhf chroot going, thanks to markos for pointing me at using multistrap I put the following in a armhfmultistrap.conf and did multistrap -f armhfmultistrap.conf Once that's done, chroot in and then do dpkg --configure -a it's pretty sparse in there, but it's enough to get going. Dave ============================================== [General] arch=armhf directory=/discs/more/armhf cleanup=true noauth=true unpack=true explicitsuite=false aptsources=unstable unreleased bootstrap=unstable unreleased [unstable] packages= source=http://ftp.de.debian.org/debian-ports/ keyring=debian-archive-keyring suite=unstable omitdebsrc=true [unreleased] packages= source=http://ftp.de.debian.org/debian-ports/ keyring=debian-archive-keyring suite=unreleased omitdebsrc=true

15 years

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risu instruction set test harness now publicly available

by Peter Maydell

Hi. As part of my work on qemu I've written a simplistic random instruction sequence generator and test harness. To quote the README: risu is a tool intended to assist in testing the implementation of models of the ARM architecture such as qemu and valgrind. In particular it restricts itself to considering the parts of the architecture visible from Linux userspace, so it can be used to test programs which only implement userspace, like valgrind and qemu's linux-user mode. I don't particularly expect this tool to be of much general interest outside people developing either qemu or valgrind or similar models, but I have in any case made it publicly available now: http://git.linaro.org/gitweb?p=people/pmaydell/risu.git;a=tree -- PMM

15 years

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RFC: Dynamic hwcaps

by Dave Martin

Hi all, I'd be interested in people's views on the following idea-- feel free to ignore if it doesn't interest you. For power-management purposes, it's useful to be able to turn off functional blocks on the SoC. For on-SoC peripherals, this can be managed through the driver framework in the kernel, but for functional blocks of the CPU itself which are used by instruction set extensions, such as NEON or other media accelerators, it would be interesting if processes could adapt to these units appearing and disappearing at runtime. This would mean that user processes would need to select dynamically between different implementations of accelerated functionality at runtime. This allows for more active power management of such functional blocks: if the CPU is not fully loaded, you can turn them off -- the kernel can spot when there is significant idle time and do this. If the CPU becomes fully loaded, applications which have soft-realtime constraints can notice this and switch to their accelerated code (which will cause the kernel to switch the functional unit(s) on). Or, the kernel can react to increasing CPU load by speculatively turn it on instead. This is analogous to the behaviour of other power governors in the system. Non-aware applications will still work seamlessly -- these may simply run accelerated code if the hardware supports it, causing the kernel to turn the affected functional block(s) on. In order for this to work, some dynamic status information would need to be visible to each user process, and polled each time a function with a dynamically switchable choice of implementations gets called. You probably don't need to worry about race conditions either-- if the process accidentally tries to use a turned-off feature, you will take a fault which gives the kernel the chance to turn the feature back on. Generally, this should be a rare occurrence. The dynamic feature status information should ideally be per-CPU global, though we could have a separate copy per thread, at the cost of more memory. It can't be system-global, since different CPUs may have a different set of functional blocks active at any one time -- for this reason, the information can't be stored in an existing mapping such as the vectors page. Conversely, existing mechanisms such sysfs probably involve too much overhead to be polled every time you call copy_pixmap() or whatever. Alternatively, each thread could register a userspace buffer (a single word is probably adequate) into which the CPU pokes the hardware status flags each time it returns to userspace, if the hardware status has changed or if the thread has been migrated. Either of the above approaches could be prototyped as an mmap'able driver, though this may not be the best approach in the long run. Does anyone have a view on whether this is a worthwhile idea, or what the best approach would be? Cheers ---Dave

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