- linaro-toolchain - lists.linaro.org

Help understanding "VFP magic dust" in cortex-strings memcpy

by Alexander Monakov

Hi! I've attempted to study the implementation of memcpy for 32-bit Arm cores in Glibc (which is also found in arm-optimized-routines and first appeared in Linaro's cortex-strings project), and I came across a peculiar snippet: #ifdef USE_VFP /* Magic dust alert! Force VFP on Cortex-A9. Experiments show that the FP pipeline is much better at streaming loads and stores. This is outside the critical loop. */ vmov.f32 s0, s0 #endif This seems to imply that this NOP-like instruction affects CPU state and makes the vldr/vstr instructions that follow use different datapaths that they might otherwise? Can anyone shed more light on this, please? I was able to trace history of this code back to revision 100 in cortex-strings repository, where it appeared as part of a large rewrite by Will Newton: https://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/rev… The entire memcpy.S file in Arm optimized-routines repo can be found here: https://github.com/ARM-software/optimized-routines/blob/master/string/arm/m… Thanks! Alexander

5 years, 5 months

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High stack usage due ftree-ch

by Adhemerval Zanella

Hi Arnd, I took a look on the stack usage issue in the kernel snippet you provided [1], and as you have noted the most impact indeed come from -ftree-ch optimization. It is enabled in all optimization levels besides -Os (since besides possible increasing the stack usage it also might increase code side). I am still fulling grasping what free-ch optimization does, but my understanding so far is it tries to reorganize the loop for later loop optimization phases. More specifically, what it ends up doing on the specific snippet is create extra stack variables for the internal membber access in the inner loop (which in its turns increase stack usage). This is also why adding the compiler barrier inhibits the optimization, since it prevents the ftree-ch to optimize the internal loop reorganization and it is passed as is to later optimizations phases. It is also a generic pass that affects all architecture, albeit the resulting stack will depend on later passes. With GCC 9.2.1 I see the resulting stack usage using -fstack-usage along with -O2: arm 632 aarch64 448 powerpc 912 powerpc64le 560 s390 600 s390x 632 i386 1376 x86_64 784 Also, -fconserve-stack does not really help with this pass since ftree-ch does not check the flag usage. The fconserve-stack currently only seems to effect the inliner by setting both large-stack-frame and large-stack-frame-growth to some conservative values. The straightforward change I am checking is just to disable tree-ch optimization if fconserve-stack is also enabled: diff --git a/gcc/tree-ssa-loop-ch.c b/gcc/tree-ssa-loop-ch.c index b894a7e0918..b14dd66257c 100644 --- a/gcc/tree-ssa-loop-ch.c +++ b/gcc/tree-ssa-loop-ch.c @@ -291,7 +291,8 @@ public: {} /* opt_pass methods: */ - virtual bool gate (function *) { return flag_tree_ch != 0; } + virtual bool gate (function *) { return flag_tree_ch != 0 + && flag_conserve_stack == 0; } /* Initialize and finalize loop structures, copying headers inbetween. */ virtual unsigned int execute (function *); On powerpc64le with gcc master: $ /home/azanella/gcc/gcc-git-build/gcc/xgcc -B /home/azanella/gcc/gcc-git-build/gcc -O2 ../stack_usage.c -c -fstack-usage && cat stack_usage.su ../stack_usage.c:157:6:mlx5e_grp_sw_update_stats 496 static $ /home/azanella/gcc/gcc-git-build/gcc/xgcc -B /home/azanella/gcc/gcc-git-build/gcc -O2 ../stack_usage.c -c -fstack-usage -fconserve-stack && cat stack_usage.su ../stack_usage.c:157:6:mlx5e_grp_sw_update_stats 176 static The reference for minimal stack usage is with -Os: $ /home/azanella/gcc/gcc-git-build/gcc/xgcc -B /home/azanella/gcc/gcc-git-build/gcc -Os ../stack_usage.c -c -fstack-usage && cat stack_usage.su ../stack_usage.c:157:6:mlx5e_grp_sw_update_stats 32 static I will try to check if also enable the same test for -fgcse and -free-ter do make sense. [1] https://godbolt.org/z/WKa-Bd

5 years, 5 months

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[Activity] Nov 18th ~ Nov 22nd 2019

by Luis Machado

# Progress # o Upstream GDB * Make remote packet length in debugging output adjustable (as opposed to fix to 512 bytes). * Investigated ARM sim build issues with the GCC default moving to -fno-common. o GDB: * GNU-644 - [GDB, AArch64] gdb.base/step-over-syscalls.exp failures - No progress yet. Waiting for Kernel feedback. * [RESOLVED] GNU-645 - gdbserver is not using SVE register descriptions properly - Pushed a fix upstream. * GNU-170 - GDB BZ #21221 - gdb hangs while stepping an empty loop - On hold for now. o Friday off # Plan # o Upstream GDB * Fox -fno-common build issues with ARM sim. o GDB * GNU-644 - [GDB, AArch64] gdb.base/step-over-syscalls.exp failures - Continue working on a fix.

5 years, 5 months

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[ACTIVITY] 18 - 22 Nov 2019

by Prathamesh Kulkarni

== This Week == * GCC - PR92554: Spent some time triaging the issue, but gave up after Richard posted better fix. - PR89007: Addressing upstream suggestions. - PR92608: Committed fix to trunk. - GNU-583: Looking thru Kugan's patch and upstream discussion. * Validation - Submitted patch to add --gcc_patch_file option to abe. - Submitted patch to remove --interactive from abe. == Next Week == - Continue ongoing tasks

5 years, 5 months

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[ACTIVITY] 18-22 Nov 2019

by Christophe Lyon

== Progress == * GCC: - -mpure-code on v6m: sent an updated patch, waiting for approval. * BFD Linker: - non-contiguous memory support: partial prototype working on the use-case, but causes regressions. * GCC upstream validation: - reported several issues * misc: - infra fixes / troubleshooting / reviews == Next == * GCC: pure-code/v6m, handle feedback * Binutils: support non-contiguous memory regions in linker

5 years, 5 months

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[ACTIVITY] week ending Nov. 24 2019

by Alex Bennée

QEMU Tooling ([VIRT-252]) ========================= Extend gdbstub for SVE ([VIRT-281]) - worked on [v2 rebase addressing comments] [VIRT-281] https://projects.linaro.org/browse/VIRT-281 [v2 rebase addressing comments] https://github.com/stsquad/qemu/tree/gdbstub/sve-registers-v2 Upstream Work ([VIRT-109]) ========================== - general poking around and stress testing on the run up to release - documented some outstanding issues [on the planning page] - posted {PULL for rc3 0/5} a few doc and testing tweaks Message-Id: <20191120105801.2735-1-alex.bennee(a)linaro.org> - posted {PATCH for 4.2 v1 0/3} some tests/vm fixes Message-Id: <20191122112231.18431-1-alex.bennee(a)linaro.org> [VIRT-109] https://projects.linaro.org/browse/VIRT-109 [on the planning page] https://wiki.qemu.org/Planning/4.2 Other Activities ================ - finalising [draft of KVM Forum conference report] - will publish on Monday once Beata adds the last note [draft of KVM Forum conference report] https://collaborate.linaro.org/pages/resumedraft.action?draftId=128647720 Completed Reviews [3/3] ======================= {PATCH v2 0/6} Make the qemu_logfile handle thread safe. Message-Id: <20191115131040.2834-1-robert.foley(a)linaro.org> - CLOSING NOTE [2019-11-22 Fri 17:15] Ad of v3 this is ready to go, just awaiting the tree to open again Added: <2019-11-15 Fri> {PATCH v3 0/6} Make the qemu_logfile handle thread safe. Message-Id: <20191118211528.3221-1-robert.foley(a)linaro.org> {PATCH 0/6} Enable Travis builds on arm64, ppc64le and s390x Message-Id: <20191119170822.45649-1-thuth(a)redhat.com> Current Review Queue ==================== * {PATCH 0/1} tests/vm: Allow to set path to qemu-img Message-Id: <20191114134246.12073-1-wainersm(a)redhat.com> Added: <2019-11-14 Thu> * {PATCH v7 0/8} Acceptance test: Add "boot_linux" acceptance test Message-Id: <20191104151323.9883-1-crosa(a)redhat.com> Added: <2019-11-04 Mon> * {RFC 0/3} tests/vhost-user-fs-test: add vhost-user-fs test case Message-Id: <20191025100152.6638-1-stefanha(a)redhat.com> Added: <2019-10-25 Fri> * {PATCH v5 00/22} target/arm: Implement ARMv8.5-MemTag, system mode Message-Id: <20191011134744.2477-1-richard.henderson(a)linaro.org> Added: <2019-10-11 Fri> -- Alex Bennée

5 years, 5 months

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[ACTIVITY] Week ending 22nd November

by Peter Smith

[Morello] - LLD finished pre-review refactoring and splitting up into reviewable chunks - Implemented range-extension and interworking thunks to test interaction with aligning .text to comply with Cheri Concentrate - Answered some questions from Linaro tech-leads about Morello Plans - Rebase once CUCL merge has been completed and submit for review. Planned Absences: Christmas Holiday 16th December - 3rd January inclusive

5 years, 5 months

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[ACTIVITY] report week ending 22 Nov

by Peter Maydell

Progress: * VIRT-65 [QEMU upstream maintainership] - code review: + Marc-Andre's series trying to get rid of QOM pointer properties + various minor bits for rc2 - unsuccessfully tried to work out why one of QEMU's test cases asserts on BSD hosts only - some time consumed by office-move thanks -- PMM

5 years, 5 months

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[ACTIVITY] 18 - 22 Nov 2019

by Diana Picus

== Progress == * Triaging check-lldb failures on AArch64 [LLVM-512] - Opened 4 bug reports - One of them got a lot of attention so I was asked to upload more logs/try various things - Still have a couple of test failures to look into * Morello - First contact with the team - Started looking at the internal docs - Trying to build the existing toolchain == Plan == * Figure out the current state of LLDB for Morello and what needs to be done * Continue triaging LLDB failures

5 years, 5 months

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Question about toolchain

by Saeed Jamali

Dear Linaro, Dear Linaro I'm using arm cortex A53 (mt6735 [part number]). But I do not know which tool-chain I have to use. I found your website https://www.linaro.org/downloads/ on internet. and my guess is aarch64-linux-gnu. can you please guide me through selecting a proper tool-chain. Regards, Saeed Djamali

5 years, 5 months

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[Activity] Nov 11th ~ Nov 15th 2019

by Luis Machado

# Progress # o Upstream GDB * More patch reviewing and answering questions. o GDB: * GNU-644 - [GDB, AArch64] gdb.base/step-over-syscalls.exp failures - Managed to track this down all the way to the aarch64 single-stepping infrastructure in the kernel. Created reproduction steps and sent an e-mail to linux-arm-kernel - Also noticed a difference in the order in which SIGCHLD's are delivered between x86_64 and aarch64. This confused GDB, which expects the ordering it sees on x86_64. Working on a fix. * Tweaked QEMU setup a little for SVE testing * GNU-645 - gdbserver is not using SVE register descriptions properly - Tracked down why gdbserver is not sending SVE register data back to GDB. Working on a fix. * GNU-170 - GDB BZ #21221 - gdb hangs while stepping an empty loop - On hold for now. # Plan # o GDB * GNU-644 - [GDB, AArch64] gdb.base/step-over-syscalls.exp failures - Continue working on a fix. * GNU-645 - gdbserver is not using SVE register descriptions properly - Continue working on a fix.

5 years, 6 months

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[ACTIVITY] week ending 17 Nov 2019

by Richard Henderson

[VIRT-262 # ARMv8.1-PAN Privileged Access Never] Started, based on VHE patch set due to mmu_idx reorg therein. Needs some minor re-work to handle Secure EL1. [VIRT-273 # ARMv8.2-ATS1E1, AT S1E1R and AT S1E1W instruction variants ] Started. [VIRT-327 # Richard's upstream QEMU work ] Some soft-freeze bug fixing of stuff that I broke this cycle. Some patch review. [Kernel] Posted v7 of the ARMv8.5-RNG patch set. There's some significant mis-communication going on between me and Mark Rutland; I have no idea what he wants at this point... [GCC] Committed the base asm-flags patch set. Posted a follow-up to un-break thumb1, and add tests for it. r~

5 years, 6 months

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[ACTIVITY] Week 46

by Yvan Roux

* One day off o LLVM: * Machine Outliner: - Identified issues with asm statements, working on a fix. o Misc * Various meetings and discussions.

5 years, 6 months

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[ACTIVITY] 11 - 15 Nov 2019

by Prathamesh Kulkarni

== This Week == * GCC - PR89007: Posted patch upstream. - GNU-583: Worked with Kugan, to reproduce LTO failure and verified his patch fixes it. - Bug 5479: Investigated with Maxim, most likely a glibc issue. * Validation: - Posted abe patch to add --gcc_patch_file option. == Next Week == - Continue ongoing tasks.

5 years, 6 months

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[ACTIVITY] 11-15 Nov 2019

by Christophe Lyon

Monday off == Progress == * GCC: - -mpure-code on v6m: answered questions about my patch. Almost OK * Linker: - started looking at implementing non-contiguous memory support * GCC upstream validation: - reported several issues * misc: - infra fixes / troubleshooting / reviews == Next == * GCC: pure-code/v6m, handle feedback * Binutils: support non-contiguous memory regions in linker

5 years, 6 months

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[ACTIVITY] Week ending 15th November 2019

by Peter Smith

[Morello] - Dynamic linking implementation complete and tests written based on GNU ld output. - Good progress on refactoring the work prior to breaking it down into reviewable chunks. Have got a good idea of what I'd like the implementation to look like. TODO: - Finish refactoring patches. - Rebase into reviewable patches. - Document the design decisions. - Test on more than just the examples in the toolchain. - Rebase on top of latest CUCL drop when merge is finished. [Other] LLVM-MC upstream review for the Linux Kernel.

5 years, 6 months

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[ACTIVITY] week ending Nov. 17 2019

by Alex Bennée

QEMU Tooling ([VIRT-252]) ========================= QEMU plugin support ([VIRT-280]) - feature now merged in 4.2 - closed out a bunch of related JIRA cards - API version now merged and this card is closed Extend gdbstub for SVE ([VIRT-281]) - posted {RFC PATCH 00/11} gdbstub re-factor and SVE support Message-Id: <20191115173000.21891-1-alex.bennee(a)linaro.org> [VIRT-281] https://projects.linaro.org/browse/VIRT-281 [working prototype] https://github.com/stsquad/qemu/tree/gdbstub/sve-registers Upstream Work ([VIRT-109]) ========================== - posted {PULL 0/8} testing and tcg plugin api ver Message-Id: <CAFEAcA_9AwoTE9zaKbiF6DkpN+O8LaEKGOct-m5S3yvFBHGK1g(a)mail.gmail.com> - posted {PATCH for 4.2-rc2 v1 0/5} misc doc and testing fixes Message-Id: <20191113115952.775-1-alex.bennee(a)linaro.org> - posted {RFC PATCH} scripts/tap-driver: report "slow" tests (HACK) Message-Id: <20191113142101.30280-1-alex.bennee(a)linaro.org> Other Activities ================ - wrote [draft of KVM Forum conference report] [draft of KVM Forum conference report] https://collaborate.linaro.org/pages/resumedraft.action?draftId=128647720 Completed Reviews [5/5] ======================= {PATCH 0/2} replace sysconf(_SC_PAGESIZE) with qemu_real_host_page_size Message-Id: <20191015031350.4345-2-richardw.yang(a)linux.intel.com> {PATCH v2 0/4} arm/aspeed: Watchdog and SDRAM fixes Message-Id: <20191113005201.19005-1-joel(a)jms.id.au> {kvm-unit-test PATCH 0/5} Improvements for the Travis CI Message-Id: <20191113112649.14322-6-thuth(a)redhat.com> {PATCH} target/arm: Clean up arm_cpu_vq_map_next_smaller asserts Message-Id: <20191115131623.322-1-richard.henderson(a)linaro.org> {PATCH v1 0/5} Make the qemu_logfile handle thread safe. Message-Id: <20191112150105.2498-1-robert.foley(a)linaro.org> Current Review Queue ==================== * {PATCH v2 0/6} Make the qemu_logfile handle thread safe. Message-Id: <20191115131040.2834-1-robert.foley(a)linaro.org> Added: <2019-11-15 Fri> * {PATCH 0/1} tests/vm: Allow to set path to qemu-img Message-Id: <20191114134246.12073-1-wainersm(a)redhat.com> Added: <2019-11-14 Thu> * {PATCH v7 0/8} Acceptance test: Add "boot_linux" acceptance test Message-Id: <20191104151323.9883-1-crosa(a)redhat.com> Added: <2019-11-04 Mon> * {RFC 0/3} tests/vhost-user-fs-test: add vhost-user-fs test case Message-Id: <20191025100152.6638-1-stefanha(a)redhat.com> Added: <2019-10-25 Fri> -- Alex Bennée

5 years, 6 months

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[ACTIVITY] report week ending 15 Nov

by Peter Maydell

Progress: * VIRT-65 [QEMU upstream maintainership] - wrote up first draft of requirements for the better CI setup for testing pull request merge builds (https://wiki.qemu.org/Requirements/GatingCI) - wrote up version of the QEMU Summit minutes that includes enough context to make sense to people who weren't present; plan to send to qemu-devel next Friday - got 4.2 rc1 out of the door; this release seems to be pleasantly quiet for a change. thanks -- PMM

5 years, 6 months

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[ACTIVITY] 11 - 15 November 2019

by Diana Picus

== Progress == * Committed SVE-related fix for InstCombine * Started triaging check-lldb failures on AArch64 [LLVM-512] - Committed a trivial fix for one of the tests - Still looking into the other failures * Received and setup laptop for Morello work - Awaiting further instructions == Plan == * Start working on Morello * Keep triaging check-lldb failures * If time permits, look into SVE asserts some more

5 years, 6 months

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[Activity] Oct 28th - Nov 6th 2019

by Luis Machado

# Progress # o Annual Review * Concluded o Upstream GDB * Patch reviews on gerrit and answering questions. * Fixed PR25124 - [ARM] regression: thumb-bx-pc.exp (https://sourceware.org/bugzilla/show_bug.cgi?id=25124) * Investigated an odd failure in gdb.base/step-over-syscall.exp and ended up finding some odd stepping behavior that may or may not be kernel related. Still investigating under GNU-644 (https://projects.linaro.org/browse/GNU-644) o GDB: * GNU-170 - GDB BZ #21221 - gdb hangs while stepping an empty loop - On hold for now. It would be nice to be able to use a NOP instead of a dummy label + jump. * Setup QEMU for running SVE bits and reproduced some SVE hiccups in gdbserver that Alex mentioned. * Misc discussions about SVE and the GDB implementation in general. # Plan # o Upstream GDB * More patch reviewing and answering questions. o GDB: * GNU-644 - [GDB, AArch64] gdb.base/step-over-syscalls.exp failures - Continue investigating * Tweak QEMU setup a little for SVE testing

5 years, 6 months

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ACTIVITY] 4-8 Nov 2019

by Christophe Lyon

== Progress == * GCC: - -mpure-code on v6m: no feedback yet * Linker: - started looking at implementing non-contiguous memory support * GCC upstream validation: - reported several issues * misc: - infra fixes / troubleshooting / reviews == Next == * GCC: pure-code/v6m, handle feedback * Binutils: support non-contiguous memory regions in linker

5 years, 6 months

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[ACTIVITY] week ending 10 Nov 2019

by Richard Henderson

[VIRT-263 # ARMv8.1-VHE Virtual Host Extensions ] Reworked the timer redirection. Now the EL2 and EL0 redirection is unified, which is a bit easier to understand. Still no joy working out where the unwanted interrupt is coming from. As far as I can tell everything is plumbed correctly... I'll shelve this until PMM is not swamped with release work. It must wait for 5.0 for merging anyway. [VIRT-327 # Richard's upstream QEMU work ] Assorted patch review. [Kernel] Posted two more rounds of ARMv8.5-RNG for review. Seems I'd misunderstood one of Mark's previous suggestions, and Ard changed his mind about how RNDR vs RNDRRS should be used in the context of the shared resource across host*CORES + virt*VCPUS. [GCC] Posted an implementation of asm-flag-output for AArch32+AArch64. I should have done this years ago. There are two potential users within the kernel, and one is access_ok() which has thousands of uses. (Oh, and RNG, which has like 3 uses. :-P) Reviewed some arm simd patches that caught my eye. r~

5 years, 6 months

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[ACTIVITY] week ending Nov. 10 2019

by Alex Bennée

QEMU Tooling ([VIRT-252]) ========================= QEMU plugin support ([VIRT-280]) - feature now merged in 4.2 - closed out a bunch of related JIRA cards - posted {PATCH} tcg plugins: expose an API version concept Message-Id: <20191104131836.12566-1-alex.bennee(a)linaro.org> - requested by Peter before hardfreeze Extend gdbstub for SVE ([VIRT-281]) - got a [working prototype] - probably need a little core gdbstub re-factor before posting RFC [VIRT-281] https://projects.linaro.org/browse/VIRT-281 [working prototype] https://github.com/stsquad/qemu/tree/gdbstub/sve-registers Upstream Work ([VIRT-109]) ========================== - posted {PULL v3 00/15} testing updates Message-Id: <20191025193709.28783-1-alex.bennee(a)linaro.org> - had to drop NetBSD autobuild (again) [VIRT-109] https://projects.linaro.org/browse/VIRT-109 [branch] https://github.com/stsquad/qemu/tree/testing/docker-multiarch-refactor [testing/next] https://github.com/stsquad/qemu/tree/testing/next Other Activities ================ - Presented at KVM Forum - went down well, made a number of contacts who are interested - A bunch of discussion on Hexagon - More detailed write-up to follow Completed Reviews [4/4] ======================= {PATCH 0/5} travis.yml improvements: Update libraries, build with arm64 Message-Id: <20191009170701.14756-1-thuth(a)redhat.com> - CLOSING NOTE [2019-10-18 Fri 19:04] Pulled some bits into testing/next Added: <2019-10-09 Wed> {PATCH} Semihost SYS_READC implementation (v4) Message-Id: <20191024224622.12371-1-keithp(a)keithp.com> {PATCH v2 0/4} target/arm: Support for Data Cache Clean up to PoP Message-Id: <CADSWDztHetgmbUOp4WyRAkR0daAG6kkwhUTcyKWiCTWHQ1XB=w(a)mail.gmail.com> {PATCH 0/4} Make the qemu_logfile handle thread safe. Message-Id: <20191107142613.2379-1-robert.foley(a)linaro.org> Absences ======== - KVM Forum Oct 29th-Nov 1st Current Review Queue ==================== * {PATCH v7 0/8} Acceptance test: Add "boot_linux" acceptance test Message-Id: <20191104151323.9883-1-crosa(a)redhat.com> Added: <2019-11-04 Mon> * {RFC 0/3} tests/vhost-user-fs-test: add vhost-user-fs test case Message-Id: <20191025100152.6638-1-stefanha(a)redhat.com> Added: <2019-10-25 Fri> * {PATCH v5 00/22} target/arm: Implement ARMv8.5-MemTag, system mode Message-Id: <20191011134744.2477-1-richard.henderson(a)linaro.org> Added: <2019-10-11 Fri> * {PATCH v4 0/9} target/arm/kvm: enable SVE in guests Message-Id: <20190924113105.19076-1-drjones(a)redhat.com> Added: <2019-09-24 Tue> -- Alex Bennée

5 years, 6 months

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[ACTIVITY] 3x3 for week ending 8th November 2019

by Peter Smith

Morello - Started to document the LLD implementation. - Implemented CHERI concentrate alignment for the important sections. - Dynamic linking is feature complete, but not finished yet, still Todo: -- More test cases for the various different combinations. -- Refactor to clean up the implementation. -- Rebase all the patches to remove the false starts. -- Update the documentation I've just started as it is already out of date. -- Not looked at ifunc or TLS yet. llvm-mc Some review on MC patch to allow limited symbolic computation when evaluating .if

5 years, 6 months

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[ACTIVITY] report week ending 8 Nov (inc KVM Forum trip report)

by Peter Maydell

Progress / KVM Forum trip report: * As usual, we held the QEMU Summit at the same time as the forum; this is an hour-or-two invitation only meeting of the top 20 or so maintainers/submaintainers, discussing process and other project issues. A proper summary/writeup of the minutes will be posted to qemu-devel later, but IMHO this year the most interesting topics were: - Spreading the load of managing pull request merges; currently I do this with the aid of some hand-hacked scripts. To be able to spread this work among more people we need to replace that with a more maintained and standardized CI/testing setup. RedHat have agreed to provide some people to work on at least the initial setup part of this, and we got some consensus that the approach to take was to use Gitlab with some custom 'runners' to handle the 'build/test on aarch64/ppc/s390x/etc' parts. - We talked about the project's general stance on 'plugin' interfaces; which can be controversial both because they commit us to maintaining a stable API/ABI and because they have the potential to be used to work around the GPL (eg proprietary device models). We plan to write up some guidelines here (mostly just writing down the existing consensus). - We also talked (again) about our handling of security issues and CVEs. My impression is that there are some parts of this that people aren't hugely happy with but that nobody has the time/effort to try to improve things (eg better documentation/tracking of issues, more prompt upstream point releases with security fixes), so things are likely to stay about as they are now. * Interesting talks (videos are being uploaded to: https://www.youtube.com/channel/UCRCSQmAOh7yzgheq-emy1xA ): - 'The Hype Around the RISC-V Hypervisor' : the RISC-V architecture's hypervisor extension isn't completely finalized yet, but it's far enough advanced that KVM support and also QEMU emulation of it have been written. An amusing sign of the architecture's academic underpinnings is that this first version doesn't have any hardware acceleration of the interrupt controller, but does have full nested-virtualization support. - 'ZERO: Next Generation Virtualization Platform for Huawei Cloud': Huawei describe hardware for a cloud environment which offloads as much as possible of the hypervisor work to custom I/O cards and a custom silicon cloud-control device, in a general approach that's probably familiar to anybody who watched the Amazon Nitro presentation from the other year. - 'What's Going On? Taking Advantage of TCG's Total System Awareness': Alex Bennée's talk on the introspection plugin work we've been doing in Linaro (and which will be in QEMU 4.2). - 'Playing Lego with Virtualization Components': description of the Rust 'rust-vmm' set of libraries intended to provide useful building blocks for putting together virtual machine managers (like Firecracker, crosvm). Basically similar content to a presentation they did for Cambridge University earlier this year, but this talk's been recorded so is good if you weren't in the audience the first time around. * And as always the in-person networking is valuable: - Oracle have a "split device emulation into separate processes" idea that's alarmingly invasive of the source code, but Stefan came up with an approach that might let them do what they need without making the source code harder to work with for the rest of us. - Met the RedHat person who's going to do the CI-for-pullreqs work (see QEMU Summit item earlier) : getting this unstalled was probably the most useful concrete outcome of the conference - Finally met Aurelien Jarno (a longstanding hobbyist contributor to QEMU who usually can't attend these conferences) * While at the conference Drew and I managed to finally get the SVE support for KVM guests into master (the last hurdle was an awkward test failure on the aarch32-compat-on-aarch64-kernel setup I happen to use as one of my build test environments; we don't care about whether KVM really works in this setup but we need 'make check' to not fail) * Also managed to fit in some wrangling of pull requests; the timing of the 4.2 release unfortunately put softfreeze on the Tuesday before the conference and rc0 on the Tuesday afterwards; rc0 ended up being postponed a couple of days as a consequence. thanks -- PMM

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