delta/go-git.git/src/runtime, branch dev.cmdgo

all: replace runtime SSE2 detection with GO386 setting

2021-08-23T21:22:58+00:00

When GO386=sse2 we can assume sse2 to be present without
a runtime check. If GO386=softfloat is set we can avoid
the usage of SSE2 even if detected.

This might cause a memcpy, memclr and bytealg slowdown of Go
binaries compiled with softfloat on machines that support
SSE2. Such setups are rare and should use GO386=sse2 instead
if performance matters.

On targets that support SSE2 we avoid the runtime overhead of
dynamic cpu feature dispatch.

The removal of runtime sse2 checks also allows to simplify
internal/cpu further by removing handling of the required
feature option as a followup after this CL.

Change-Id: I90a853a8853a405cb665497c6d1a86556947ba17
Reviewed-on: https://go-review.googlesource.com/c/go/+/344350
Trust: Martin Möhrmann 
Run-TryBot: Martin Möhrmann 
TryBot-Result: Go Bot 
Reviewed-by: Keith Randall

runtime: use RDTSCP for instruction stream serialized read of TSC

2021-08-23T20:32:04+00:00

To measure all instructions having been completed before reading
the time stamp counter with RDTSC an instruction sequence that
has instruction stream serializing properties which guarantee
waiting until all previous instructions have been executed is
needed. This does not necessary mean to wait for all stores to
be globally visible.

This CL aims to remove vendor specific logic for determining the
instruction sequence with CPU feature flag checks that are
CPU vendor independent.

For intel LFENCE has the wanted properties at least
since it was introduced together with SSE2 support.

On AMD instruction stream serializing LFENCE is supported by setting
an MSR C001_1029[1]=1 on AMD family 10h/12h/14h/15h/16h/17h processors.
AMD family 0Fh/11h processors support LFENCE as serializing always.
AMD plans support for this MSR and access to this bit for all future processors.
Source: https://developer.amd.com/wp-content/resources/Managing-Speculation-on-AMD-Processors.pdf

Reading the MSR to determine LFENCE properties is not always possible
or reliable (hypervisors). The Linux kernel is relying on serializing
LFENCE on AMD CPUs since a commit in July 2019: https://lkml.org/lkml/2019/7/22/295
and the MSR C001_1029 to enable serialization has been set by default
with the Spectre v1 mitigations.

Using an MFENCE on AMD is waiting on previous instructions having been executed
but in addition also flushes store buffers.

To align the serialization properties without runtime detection
of CPU manufacturers we can use the newer RDTSCP instruction which
waits until all previous instructions have been executed.

RDTSCP is available on Intel since around 2008 and on AMD CPUs since
around 2006. Support for RDTSCP can be checked independently
of manufacturer by checking CPUID bits.

Using RDTSCP is the default in Linux to read TSC in program order
when the instruction is available.
https://github.com/torvalds/linux/blob/e22ce8eb631bdc47a4a4ea7ecf4e4ba499db4f93/arch/x86/include/asm/msr.h#L231

Change-Id: Ifa841843b9abb2816f8f0754a163ebf01385306d
Reviewed-on: https://go-review.googlesource.com/c/go/+/344429
Reviewed-by: Keith Randall
Trust: Martin Möhrmann
Run-TryBot: Martin Möhrmann
TryBot-Result: Go Bot

runtime: remove unused cpu architecture feature variables from binaries

2021-08-23T11:23:58+00:00

On amd64 this reduces go binary sizes by 176 bytes due to not referencing
internal/cpu.ARM64 and internal/cpu.ARM.

Change-Id: I8e4f31e2b1939b05eec2148b44d7cff7e0aeb30e
Reviewed-on: https://go-review.googlesource.com/c/go/+/344329
Trust: Martin Möhrmann 
Run-TryBot: Martin Möhrmann 
Reviewed-by: Tobias Klauser 
TryBot-Result: Go Bot

runtime: use asmcgocall_no_g when calling sigprocmask on openbsd

2021-08-22T13:54:24+00:00

sigprocmask is called from sigsave, which is called from needm. As such,
sigprocmask has to be able to run with no g. For some reason we do not
currently trip this on current libc platforms, but we do hit it on
openbsd/mips64 with external linking.

Updates #36435

Change-Id: I4dfae924245c5f68cc012755d6485939014898a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/334879
Trust: Joel Sing 
Reviewed-by: Ian Lance Taylor

runtime: fix buckHashSize duplication

2021-08-22T13:11:50+00:00

We have a constant for 179999, don't duplicate it.

Change-Id: Iefb9c4746f6dda2e08b42e3c978963198469ee8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/277375
Reviewed-by: Keith Randall 
Run-TryBot: Keith Randall 
Run-TryBot: Michael Pratt 
TryBot-Result: Go Bot 
Trust: Michael Pratt

syscall: add SyscallN

2021-08-19T17:30:19+00:00

This CL adds a new syscall.SyscallN API.

The proposal discussion also suggests the API should not only for
Windows but other platforms. However, the existing API set already
contain differences between platforms, hence the CL only implements
the Windows platform.

Moreover, although the API offers variadic parameters, the permitted
parameters remains up to a limit, which is selected as 42, and arguably
large enough.

Fixes #46552

Change-Id: I66b49988a304d9fc178c7cd5de46d0b75e167a4f
Reviewed-on: https://go-review.googlesource.com/c/go/+/336550
Run-TryBot: Ian Lance Taylor 
TryBot-Result: Go Bot 
Reviewed-by: Ian Lance Taylor 
Reviewed-by: Matthew Dempsky 
Trust: Matthew Dempsky 
Trust: Jason A. Donenfeld

runtime: use RDCYCLE for cputicks on riscv64

2021-08-18T02:08:09+00:00

Use RDCYCLE instruction instead of RDTIME emulation

Change-Id: Id7b3de42a36d2d1b163c39cc79870eee7c840ad5
Reviewed-on: https://go-review.googlesource.com/c/go/+/332954
Trust: Meng Zhuo 
Reviewed-by: Cherry Mui

all: fix typos

2021-08-17T13:54:10+00:00

Change-Id: I83180c472db8795803c1b9be3a33f35959e4dcc2
Reviewed-on: https://go-review.googlesource.com/c/go/+/336889
Reviewed-by: Rob Pike 
Reviewed-by: Austin Clements

runtime: accept restartable sequence pcdata values in isAsyncSafePoint

2021-08-16T23:32:14+00:00

If the pcdata value indicates a restartable sequence, it is okay
to asynchronously preempt (and resume at the restart PC). Accept
it in isAsyncSafePoint.

Fixes #47530.

Change-Id: I419225717c8eee5812f3235338262da5895aad0d
Reviewed-on: https://go-review.googlesource.com/c/go/+/340011
Trust: Cherry Mui 
Run-TryBot: Cherry Mui 
Reviewed-by: Joel Sing 
Reviewed-by: Austin Clements

runtime: skip sysmon workaround on NetBSD >= 9.2

2021-08-16T21:24:44+00:00

Detect the NetBSD version in osinit and only enable the workaround for
the kernel bug identified in #42515 for NetBSD versions older than 9.2.

For #42515
For #46495

Change-Id: I808846c7f8e47e5f7cc0a2f869246f4bd90d8e22
Reviewed-on: https://go-review.googlesource.com/c/go/+/324472
Trust: Tobias Klauser 
Trust: Benny Siegert 
Run-TryBot: Tobias Klauser 
Reviewed-by: Michael Pratt 
Reviewed-by: Ian Lance Taylor 
TryBot-Result: Go Bot