[LLVM-158] buildbot maintenance
- Increased timeouts on some libfuzzer tests, aarch64 full bots should
fail less frequently under load.
[LLVM-534] -n -N support in LLD (needed for Linux kernel allyesconfig
CI with LLD on AArch64)
Rewrote using a different approach after upstream comments
[LLVM-122] BTI and PAC support in LLD
Wrote an implementation, it compiles, but completely untested as of today.
(short week: 3 days)
Brief writeup of a pair of talks I attended on Tuesday at the
Cambridge University Computer Lab by some people from Amazon:
Diana Popa talked about Amazon's new "Firecracker" VMM (virtual
machine monitor -- the userspace component that uses the kernel's KVM
APIs to create and control virtual machines; kvmtool and QEMU are both
VMMs). Their use case is the AWS Lambda service, where VMs are
generally fairly short-lived (on the order of hours), startup time
matters a lot, and the VMs typically don't need very much CPU/RAM
resource. Firecracker is written in Rust, and provides a very simple
guest device model (virtio block and network devices), booting a
kernel that knows it is virtualized. It boots the kernel directly,
without running a BIOS. It has a memory footprint of less than 5MB and
a boot time of 125ms. They are currently working on Arm support (they
have it booting, but some bits still need work, eg the VM doesn't get
the right time because there is no RTC device exposed to the guest).
My feeling was that this shows an advantage of the KVM design: the
kernel/userspace split makes it easy to replace the userspace VMM
part with something customised for the task at hand if you don't
need a full-fat all-bells-and-whistles general-purpose solution.
Andreea Florescu talked next, about the "rust-vmm" libraries. This is
a set of open-source Rust crates which are intended to abstract out
some of the common building blocks for VMMs. Firecracker started as a
fork of Google's crosvm project, but since the use-case requirements
for the two projects are markedly different the code diverged fairly
rapidly. rust-vmm is intended to allow the projects to share code for
things like "nice Rust interfaces to the KVM ioctls" and
"implementations of virtio devices". The project is still in quite an
early stage of development -- they have a few crates that have made it
to the "stable, published on crates.io" phase, but most are either in
"being developed" or still just "planned/proposed/discussed". It's
currently Apache-2.0 licensed, but they are planning to dual-license
to Apache-2.0 | 3-BSD because Apache-2.0 isn't GPL-2.0 compatible, and
they have had some interest in being able to experiment with using
these crates with QEMU. (That sounds a bit outlandish but it's
actually something I'm planning to look into myself -- the nice thing
about Rust is that you can potentially incrementally add it to an
existing C codebase without requiring a ground-up rewrite, so allowing
security hardening of the more "risky" parts. This is very definitely
all still just "exploratory prototyping" though.)
Progress:
* just miscellaneous upstream stuff
thanks
-- PMM
* 1 day off (public holiday)
== Progress ==
* FDPIC
- rebased GCC FDPIC patches. Fixing conflict with fstack-protector.
* GCC upstream validation:
- Fixed ST internal validation broken since GCC bumped to version 10.
Still some spurious failures probably caused by NFS. Testing
workarounds.
- reported a couple of regressions
* GCC
- ubsan on bare-metal toolchain: no news.
* Infra
- [stalled] working on adding binutils regression testing to round-robin jobs
== Next ==
FDPIC:
- GCC: fix problems with fstack-protector
UBSAN/bare-metal: look at how to make it easier to use on CPUs that
lack sync primivites (eg cortex-m0)
o 4 days week.
o LLVM
* Machine outliner:
- Identified an issue related to LR saving inside an outlined
chunk, working on a proper fix.
o Misc
* Various meetings and discussions.
[VIRT-327 # Richard's upstream QEMU work ]
Review Mark's target/ppc getVSR patch set.
Two rounds of "tcg vector improvments"; hopefully that's
ready to go in on Monday.
More work on "bit select" and "compare select" primitives.
I can now vectorize Neon VSHL/VSHR variable shift (where
positive values are left shift and negative values are
right shift). Waiting on posting this while previous tcg
vector patch set is still in flight.
Review Alex's demacrofy v5. Wrote a boot.S for Alpha.
Review David's latest target/s390 vector patch set.
Review Sato-san's target/rx v8. Played around with a few
disassembler improvements, but I'll not confuse the review
process by posting them now.
r~
Progress:
* VIRT-65 [QEMU upstream maintainership]
+ pushed QEMU 4.0 out the door
+ code review:
- RTH's patchset that cleans up the softmmu TLB structs
- Nios2 nommu and semihosting patchset from codesourcery
- cleanup series removing a "bucket of random stuff" header file
- RTH's patchset adding BTI support for linux-user mode
- RTH's patchset cleaning up the tlb_fill API
- RTH's patchset implementing Cortex-A73, A75, A76
- "SBSA reference platform" new board model
- patchset adding Netduino Plus 2 board model
- linux-user patch to correctly handle loading ELF segments which
have no file data (ie only bss)
- patch adding the RTC device to the ASpeed board models
- patchset fixing various minor problems preventing QEMU building
cleanly for Windows-on-Arm
- started looking at Damian's patchset that overhauls how we do
device reset; this is good work that's long overdue, but reviewing
it requires me to wrap my head around the problem space...
+ sent out v2 versions of a few minor patches that needed respins
+ wrote email to qemu-devel asking for volunteers to help with
QEMU release work so it's not only me doing this every cycle
* VIRT-268 [QEMU support for dual-core Cortex-M Musca board]
+ FPU support now upstream
+ a few loose ends remain to be tidied up, but this epic is
now essentially complete
NB: out of office Tues 7th afternoon to attend a couple of lectures
at the CL by people from Amazon on their virtualization stack written
in Rust (http://talks.cam.ac.uk/talk/index/119491 and
http://talks.cam.ac.uk/talk/index/121069)
thanks
-- PMM
[LLVM-158] Buildbot monitoring duty
- Reported bug that libc++ when built as part as libfuzzer is not
built with PIC or PIE, yet some tests for non-x86 force PIE which then
fails at link-time.
- Reported bugs in libstdc++ and clang where exception specifications
didn't match due to extra parentheses. libstdc++ now fixed to not have
any discrepancy, clang bug for not ignoring the extra parentheses
still active.
- Investigated libfuzzer intermittent failures, 2 look like timeouts
not being long enough, submitted patch to get this increased.
[LLVM-122] BTI/PAC Started prototyping an implementation based on top
of the yet to land LLD patch for Intel CET.
Think about how to add crypto extensions without overriding
architecture in a complex build system.
Review comments for LLD and compiler-rt, and mailing list proposal for
something similar to __attribute__((at(address))).
