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bc6c433142
It would be convenient if we did not need to use cgo to compile for FreeBSD for common architectures, allowing builds to be generated in Linux CI flows. The sysctl interface uses offsets which can vary by build architecture, so doing this in the general case without cgo is not realistic. But we can front-load the C work to get the offsets for a given architecture, then use encoding/binary at run-time. While doing this, I saw that the existing FreeBSD code was mis-calculating `%cpu` by converting the `fixpt_t` scaled int straight to a double without dividing by the scaling factor, so we also fix for all other architectures by introducing a division by `FSCALE`. The offsets-emitting code is in `freebsd.txt`, with the filename chosen to keep the Go toolchain from picking it up and trying to compile. The result is unsafe-free cgo-free builds for FreeBSD/amd64.
92 lines
3.0 KiB
Go
92 lines
3.0 KiB
Go
// Copyright 2015-2020 The NATS Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// This is the amd64-specific FreeBSD implementation, with hard-coded offset
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// constants derived by running freebsd.txt; having this implementation allows
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// us to compile without CGO, which lets us cross-compile for FreeBSD from our
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// CI system and so supply binaries for FreeBSD amd64.
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//
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// To generate for other architectures:
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// 1. Update pse_freebsd.go, change the build exclusion to exclude your arch
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// 2. Copy this file to be built for your arch
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// 3. Update `nativeEndian` below
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// 4. Link `freebsd.txt` to have a .c filename and compile and run, then
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// paste the outputs into the const section below.
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package pse
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import (
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"encoding/binary"
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"syscall"
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"golang.org/x/sys/unix"
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)
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// On FreeBSD, to get proc information we read it out of the kernel using a
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// binary sysctl. The endianness of integers is thus explicitly "host", rather
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// than little or big endian.
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var nativeEndian = binary.LittleEndian
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const (
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KIP_OFF_size = 256
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KIP_OFF_rssize = 264
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KIP_OFF_pctcpu = 308
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)
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var pageshift int
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func init() {
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// To get the physical page size, the C library checks two places:
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// process ELF auxiliary info, AT_PAGESZ
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// as a fallback, the hw.pagesize sysctl
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// In looking closely, I found that the Go runtime support is handling
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// this for us, and exposing that as syscall.Getpagesize, having checked
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// both in the same ways, at process start, so a call to that should return
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// a memory value without even a syscall bounce.
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pagesize := syscall.Getpagesize()
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pageshift = 0
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for pagesize > 1 {
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pageshift += 1
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pagesize >>= 1
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}
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}
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func ProcUsage(pcpu *float64, rss, vss *int64) error {
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rawdata, err := unix.SysctlRaw("kern.proc.pid", unix.Getpid())
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if err != nil {
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return err
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}
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r_vss_bytes := nativeEndian.Uint32(rawdata[KIP_OFF_size:])
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r_rss_pages := nativeEndian.Uint32(rawdata[KIP_OFF_rssize:])
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rss_bytes := r_rss_pages << pageshift
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// In C: fixpt_t ki_pctcpu
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// Doc: %cpu for process during ki_swtime
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// fixpt_t is __uint32_t
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// usr.bin/top uses pctdouble to convert to a double (float64)
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// define pctdouble(p) ((double)(p) / FIXED_PCTCPU)
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// FIXED_PCTCPU is _usually_ FSCALE (some architectures are special)
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// <sys/param.h> has:
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// #define FSHIFT 11 /* bits to right of fixed binary point */
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// #define FSCALE (1<<FSHIFT)
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r_pcpu := nativeEndian.Uint32(rawdata[KIP_OFF_pctcpu:])
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f_pcpu := float64(r_pcpu) / float64(2048)
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*rss = int64(rss_bytes)
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*vss = int64(r_vss_bytes)
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*pcpu = f_pcpu
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return nil
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}
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