delta/go-git.git/src/syscall/exec_linux.go, branch dev.go2go

syscall: implement rawVforkSyscall for remaining linux platforms

2021-03-03T05:33:21+00:00

This allows the use of CLONE_VFORK and CLONE_VM for fork/exec, preventing
'fork/exec ...: cannot allocate memory' failures from occuring when attempting
to execute commands from a Go process that has a large memory footprint.
Additionally, this should reduce the latency of fork/exec on these platforms.

Fixes #31936

Change-Id: I4e28cf0763173145cacaa5340680dca9ff449305
Reviewed-on: https://go-review.googlesource.com/c/go/+/295849
Trust: Joel Sing 
Run-TryBot: Joel Sing 
Reviewed-by: Cherry Zhang

all: go fmt std cmd (but revert vendor)

2021-02-20T03:54:50+00:00

Make all our package sources use Go 1.17 gofmt format
(adding //go:build lines).

Part of //go:build change (#41184).
See https://golang.org/design/draft-gobuild

Change-Id: Ia0534360e4957e58cd9a18429c39d0e32a6addb4
Reviewed-on: https://go-review.googlesource.com/c/go/+/294430
Trust: Russ Cox 
Run-TryBot: Russ Cox 
TryBot-Result: Go Bot 
Reviewed-by: Jason A. Donenfeld 
Reviewed-by: Ian Lance Taylor

syscall: support rawVforkSyscall on linux/riscv64

2020-08-16T14:23:50+00:00

Updates #31936

Change-Id: I7dcb8987d4c306ccc97704b9c1b12313ba8bf242
Reviewed-on: https://go-review.googlesource.com/c/go/+/234960
Reviewed-by: Cherry Zhang 
Run-TryBot: Cherry Zhang 
TryBot-Result: Gobot Gobot

syscall: use correct file descriptor in dup2 fallback path

2020-07-25T20:13:27+00:00

This fixes a mistake in CL 220422. This changes code that is only
executed on Linux kernel versions earlier than 2.6.27.

Change-Id: I01280184f4d7b75e06387c38f1891e8f0a81f793
Reviewed-on: https://go-review.googlesource.com/c/go/+/244630
Run-TryBot: Ian Lance Taylor 
TryBot-Result: Gobot Gobot 
Reviewed-by: Tobias Klauser

syscall: document exact meaning of Ctty field

2020-05-01T04:53:11+00:00

The Ctty field is a child descriptor number when Setctty is set,
but a parent descriptor when Foreground is set. This is absurd
but changing either behavior breaks existing programs.

With this change we at least document how it works.

For #29458

Change-Id: If9cf0a1a1e6ed0d4a4edae5043016d5b4ee3308b
Reviewed-on: https://go-review.googlesource.com/c/go/+/229768
Run-TryBot: Ian Lance Taylor 
TryBot-Result: Gobot Gobot 
Reviewed-by: Damien Neil

syscall: use dup3 in forkAndExecInChild1 if available

2020-02-24T08:31:48+00:00

The dup3 syscall is available since Linux 2.6.27. Fall back to dup2 (if
available) if dup3 returns ENOSYS.

This allows to omit the additional fcntl call to mark the dup'ed fd as
close-on-exec.

Change-Id: If318b593edd783f2aa988534c6062498e7119ddb
Reviewed-on: https://go-review.googlesource.com/c/go/+/220422
Run-TryBot: Tobias Klauser 
TryBot-Result: Gobot Gobot 
Reviewed-by: Ian Lance Taylor

syscall: use fcntl64 on 32-bit GNU/Linux systems

2019-12-30T09:34:53+00:00

Use fcntl64Syscall in forkAndExecInChild1 to get fcntl64 on 32-bit Linux
systems.

Updates #36211

Change-Id: Id0e34359256beace970e72102fdace7a987ff2b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/212598
Run-TryBot: Tobias Klauser 
TryBot-Result: Gobot Gobot 
Reviewed-by: Ian Lance Taylor

syscall: implement rawVforkSyscall for linux/arm64

2019-09-11T07:19:55+00:00

This allows the use of CLONE_VFORK and CLONE_VM for fork/exec, preventing
"fork/exec ...: cannot allocate memory" failures from occuring when attempting
to execute commands from a Go process that has a large memory footprint.
Additionally, this should reduce the latency of fork/exec on linux/arm64.

With CLONE_VM the child process shares the same memory with the parent
process. On its own this would lead to conflicting use of the same
memory, so CLONE_VFORK is used to suspend the parent process until the
child releases the memory when switching to the new program binary
via the exec syscall. When the parent process continues to run, one
has to consider the changes to memory that the child process did,
namely the return address of the syscall function needs to be restored
from a register.

exec.Command() callers can start in a faster manner, as child process who
do exec commands job can be cloned faster via vfork than via fork on arm64.

The same problem was addressed on linux/amd64 via issue #5838.

Updates #31936
Contributed by Howard Zhang  and Bin Lu 

Change-Id: Ia99d81d877f564ec60d19f17e596276836576eaf
Reviewed-on: https://go-review.googlesource.com/c/go/+/189418
Run-TryBot: Tobias Klauser 
TryBot-Result: Gobot Gobot 
Reviewed-by: Tobias Klauser 
Reviewed-by: Cherry Zhang

Revert "syscall: use Ctty before fd shuffle"

2019-06-27T16:53:02+00:00

This reverts commit 103b5b66921b351f8db4fc6e83bf147b1a0d7580.

Reason for revert: Breaks valid existing programs.

Updates #29458

Change-Id: I7ace4ae404cf2a8b0e15e646663c50115f74b758
Reviewed-on: https://go-review.googlesource.com/c/go/+/183939
Run-TryBot: Ian Lance Taylor 
TryBot-Result: Gobot Gobot 
Reviewed-by: Greg Thelen 
Reviewed-by: Ian Lance Taylor

syscall: use Ctty before fd shuffle

2019-05-30T22:02:03+00:00

On unix if exec.Command() is given both ExtraFiles and Ctty, and the
Ctty file descriptor overlaps the range of FDs intended for the child,
then cmd.Start() the ioctl(fd,TIOCSCTTY) call fails with an
"inappropriate ioctl for device" error.

When child file descriptors overlap the new child's ctty the ctty will
be closed in the fd shuffle before the TIOCSCTTY. Thus TIOCSCTTY is
used on one of the ExtraFiles rather than the intended Ctty file. Thus
the error.

exec.Command() callers can workaround this by ensuring the Ctty fd is
larger than any ExtraFiles destined for the child.

Fix this by doing the ctty ioctl before the fd shuffle.

Test for this issue by modifying TestTerminalSignal to use more
ExtraFiles. The test fails on linux and freebsd without this change's
syscall/*.go changes. Other platforms (e.g. darwin, aix, solaris) have
the same fd shuffle logic, so the same fix is applied to them. However,
I was only able to test on linux (32 and 64 bit) and freebsd (64 bit).

Manual runs of the test in https://golang.org/issue/29458 start passing
with this patch:
Before:
% /tmp/src/go/bin/go run t
successfully ran child process with ParentExtraFileFdNum=5, ChildExtraFileFd=6, ParentPtyFd=7

panic: failed to run child process with ParentExtraFileFdNum=10, ChildExtraFileFd=11, ParentPtyFd=11: fork/exec /bin/true: inappropriate ioctl for device

After:
% /tmp/src/go/bin/go run t
successfully ran child process with ParentExtraFileFdNum=5, ChildExtraFileFd=6, ParentPtyFd=7

successfully ran child process with ParentExtraFileFdNum=10, ChildExtraFileFd=11, ParentPtyFd=11

Fixes #29458
Change-Id: I99513de7b6073c7eb855f1eeb4d1f9dc0454ef8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/178919
Run-TryBot: Brad Fitzpatrick
TryBot-Result: Gobot Gobot
Reviewed-by: Ian Lance Taylor