runtime: clean up system call code #51087

prattmic · 2022-02-08T22:08:51Z

The code used to make system calls from the runtime is a mess and a big pain point when making OS-level changes in the runtime.

Quick summary of some of the pain points:

Completely independent implementation from package syscall.
System call stubs exist in a variety of OS- and arch-specific sys* files (57, to be precise, mostly assembly), totaling ~23k lines of code [1], which is 100% hand-written. Adding a new syscall stub often requires adding new assembly to 10+ files.
There is no generic Syscall function that can be used to make an arbitrary system call. You must add a new stub to make a new call.

Some things we could do to improve the situation:

Add generic Syscall functions, used by other stubs. And/or use code generation to generate stubs rather than doing so manually.
Move syscall code to a new package (like runtime/internal/syscall or perhaps runtime/internal/linux?) to avoid littering the runtime package itself with so many files.
Make package syscall depend on the runtime's Syscall stub so we only have a single implementation.

[1] Some of this code is things other than syscall stubs, like thread entrypoints.

cc @aclements @mknyszek @cherrymui

The text was updated successfully, but these errors were encountered:

aclements · 2022-02-08T22:13:57Z

And/or use code generation to generate stubs rather than doing so manually.

All or most of the information we would need to generate the stubs is already in the syscall package. The needs of the syscall package are of course a bit different, but the metadata should be effectively the same.

Orthogonal to code generation, given a generic runtime Syscall function (or a few of them for different numbers of arguments), would there even be any overhead to having the stubs be in Go rather than assembly? In addition to significantly reducing the amount of assembly, I think this would encourage us to do better error handling.

cherrymui · 2022-02-08T22:14:43Z

Just to add another pain point: the stubs handle errors differently. Some returns errno (negated or not?), some just crash hard (writing to an invalid address), which is difficult to debug sometimes.

gopherbot · 2022-02-08T22:17:32Z

Change https://go.dev/cl/383999 mentions this issue: runtime/internal/syscall: new package for linux

Add a generic syscall package for use by the runtime. Eventually we'd like to clean up system calls in the runtime to use more code generation and be moved out of the main runtime package. The implementations of the assembly functions are based on copies of syscall.RawSyscall6, modified slightly for more consistency between arches. e.g., renamed trap to num, always set syscall num register first. For now, this package is just the bare minimum needed for doAllThreadsSyscall to make an arbitrary syscall. For #51087. For #50113. Change-Id: Ibecb5e6303279ce15286759e1cd6a2ddc52f7c72 Reviewed-on: https://go-review.googlesource.com/c/go/+/383999 Trust: Michael Pratt <[email protected]> Run-TryBot: Michael Pratt <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Austin Clements <[email protected]>

ii64 · 2022-02-23T11:02:24Z

Seems this introduce build error, i got:
gofrontend commit 45fd14ab8baf5e86012a808426f8ef52c1d77943

cherrymui · 2022-02-23T14:58:43Z

@ii64 this issue is about a plan for the future, not what has happened. Your comment is unrelated to this issue.

Looks like you are using gollvm. What version of gollvm are you using? Try updating to the latest. If that still fail, please file a new issue. Thanks.

gopherbot · 2022-02-28T19:43:15Z

Change https://go.dev/cl/388094 mentions this issue: test: rename live_syscall.go to live_uintptrkeepalive.go

gopherbot · 2022-02-28T19:43:15Z

Change https://go.dev/cl/388477 mentions this issue: syscall: define Syscall in terms of RawSyscall

gopherbot · 2022-02-28T19:43:16Z

Change https://go.dev/cl/388475 mentions this issue: runtime/internal/syscall, syscall: replace RawSyscall6 with runtime implementation

gopherbot · 2022-02-28T19:43:17Z

Change https://go.dev/cl/388478 mentions this issue: syscall: define Syscall6 in terms of RawSyscall6

gopherbot · 2022-02-28T19:43:17Z

Change https://go.dev/cl/388095 mentions this issue: cmd/compile: add //go:uintptrkeepalive

gopherbot · 2022-02-28T19:43:18Z

Change https://go.dev/cl/388476 mentions this issue: syscall: define RawSyscall in terms of RawSyscall6

gopherbot · 2022-02-28T19:43:19Z

Change https://go.dev/cl/388479 mentions this issue: syscall: implement rawSyscallNoError in terms of RawSyscall

gopherbot · 2022-02-28T19:43:20Z

Change https://go.dev/cl/388474 mentions this issue: syscall: move Syscall declarations to OS files

gopherbot · 2022-04-19T20:32:11Z

Change https://go.dev/cl/401096 mentions this issue: runtime/internal/syscall: use ABIInternal for Syscall6 on amd64

gopherbot · 2022-04-20T18:38:04Z

Change https://go.dev/cl/401337 mentions this issue: DO NOT SUBMIT: WIP: support inlining with //go:uintptrkeepalive

CL 388095 will change this file significantly. Move it preemptively to ensure git tracks the move properly. For #51087 Change-Id: I1408aecf8675723041b64e54cf44cdec38cc655c Reviewed-on: https://go-review.googlesource.com/c/go/+/388094 Run-TryBot: Michael Pratt <[email protected]> Reviewed-by: Matthew Dempsky <[email protected]> Reviewed-by: David Chase <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

This CL exports the existing ir.UintptrKeepAlive via the new directive //go:uintptrkeepalive. This makes the compiler insert KeepAlives for pointers converted to uintptr in calls, keeping them alive for the duration of the call. //go:uintptrkeepalive requires //go:nosplit, as stack growth can't handle these arguments (it cannot know which are pointers). We currently check this on the immediate function, but the actual restriction applies to all transitive calls. The existing //go:uintptrescapes is an extension of //go:uintptrkeepalive which forces pointers to escape to the heap, thus eliminating the stack growth issue. This pragma is limited to the standard library. For #51087 Change-Id: If9a19d484d3561b4219e5539b70c11a3cc09391e Reviewed-on: https://go-review.googlesource.com/c/go/+/388095 Run-TryBot: Michael Pratt <[email protected]> Reviewed-by: Matthew Dempsky <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

Future CLs will be changing the provenance of these functions. Move the declarations to the individual OS files now so that future CLs can change only 1 OS at a time rather than changing all at once. For #51087 Change-Id: I5e1bca71e670263d8c0faa586c1b6b4de1a114b6 Reviewed-on: https://go-review.googlesource.com/c/go/+/388474 Run-TryBot: Michael Pratt <[email protected]> Reviewed-by: Cherry Mui <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

…mplementation on linux For #51087 Change-Id: I75a1bdeb5089454595f5ca04765a9c6e45cf9bd5 Reviewed-on: https://go-review.googlesource.com/c/go/+/388475 Run-TryBot: Michael Pratt <[email protected]> Reviewed-by: Cherry Mui <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

For #51087 Change-Id: I63e07638507328efe33dbf7dd5f8a8b78890e037 Reviewed-on: https://go-review.googlesource.com/c/go/+/388476 Run-TryBot: Michael Pratt <[email protected]> Reviewed-by: Cherry Mui <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

For #51087 Change-Id: I9de7e85ccf137ae73662759382334bcbe7208150 Reviewed-on: https://go-review.googlesource.com/c/go/+/388477 Run-TryBot: Michael Pratt <[email protected]> Reviewed-by: Cherry Mui <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

This reverts CL 401096. Grandparent CL 388477 breaks cmd/go TestScript/cover_pkgall_runtime. For #51087. For #52472. Change-Id: Ie82fe5f50975f66eb91fb0d01cd8bbbd0265eb4e Reviewed-on: https://go-review.googlesource.com/c/go/+/401634 Run-TryBot: Michael Pratt <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Reviewed-by: Bryan Mills <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

This reverts CL 388478. Parent CL 388477 breaks cmd/go TestScript/cover_pkgall_runtime. For #51087. For #52472. Change-Id: Id5d5a4e138792cf130ecdcc6b996c8102d142a7e Reviewed-on: https://go-review.googlesource.com/c/go/+/401635 Run-TryBot: Michael Pratt <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Reviewed-by: Bryan Mills <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

This reverts CL 388477, which breaks cmd/go TestScript/cover_pkgall_runtime. For #51087. For #52472. Change-Id: Id58af419a889281f15df2471c58fece011fcffbc Reviewed-on: https://go-review.googlesource.com/c/go/+/401636 Run-TryBot: Michael Pratt <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Reviewed-by: Bryan Mills <[email protected]> TryBot-Result: Gopher Robot <[email protected]>

gopherbot · 2022-04-21T20:14:03Z

Change https://go.dev/cl/401654 mentions this issue: syscall: define Syscall in terms of RawSyscall on linux

gopherbot · 2022-04-21T20:14:05Z

Change https://go.dev/cl/401656 mentions this issue: runtime/internal/syscall: use ABIInternal for Syscall6 on amd64

gopherbot · 2022-04-21T20:14:06Z

Change https://go.dev/cl/401655 mentions this issue: syscall: define Syscall6 in terms of RawSyscall6 on linux

This is a re-do of CL 388477, fixing #52472. It is unsafe to call syscall.RawSyscall from syscall.Syscall with -coverpkg=all and -race. This is because: 1. Coverage adds a sync/atomic call in RawSyscall to increment the coverage counter. 2. Race mode instruments sync/atomic calls with TSAN runtime calls. TSAN eventually calls runtime.racecallbackfunc, which expects getg().m.p != 0, which is no longer true after entersyscall(). cmd/go actually avoids adding coverage instrumention to package runtime in race mode entirely to avoid these kinds of problems. Rather than also excluding all of syscall for this one function, work around by calling RawSyscall6 instead, which avoids coverage instrumention both by being written in assembly and in package runtime/*. For #51087 Fixes #52472 Change-Id: Iaffd27df03753020c4716059a455d6ca7b62f347 Reviewed-on: https://go-review.googlesource.com/c/go/+/401654 Run-TryBot: Michael Pratt <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Reviewed-by: Cherry Mui <[email protected]>

This is an exact copy of CL 388478 after fixing #52472 in CL 401654. For #51087 For #52472 Change-Id: I6c6bd7ddcab1512c682e6b44f61c7bcde97f5c58 Reviewed-on: https://go-review.googlesource.com/c/go/+/401655 Run-TryBot: Michael Pratt <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Cherry Mui <[email protected]>

prattmic · 2022-04-22T19:54:06Z

Everything I expect to get into 1.19 is in. Moving future work to 1.20.

This is an exact copy of CL 401096 after fixing #52472 in CL 401654. For #51087 For #52472 Change-Id: Ib3c914949a15517aacdca2d72e69e1c7b217e430 Reviewed-on: https://go-review.googlesource.com/c/go/+/401656 Run-TryBot: Michael Pratt <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Cherry Mui <[email protected]>

gopherbot · 2022-04-28T15:46:53Z

Change https://go.dev/cl/402914 mentions this issue: syscall: add //go:norace to RawSyscall

RawSyscall is used in a variety of rather unsafe conditions, such as after fork in forkAndExecInChild1. Disable race instrumentation to avoid calling TSAN in unsafe conditions. For #51087 Change-Id: I47c35e6f0768c77ddab99010ea0404c45ad2f1da Reviewed-on: https://go-review.googlesource.com/c/go/+/402914 TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Cherry Mui <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Run-TryBot: Michael Pratt <[email protected]>

gopherbot · 2022-08-08T13:30:22Z

Change https://go.dev/cl/421994 mentions this issue: runtime: move epoll syscalls to runtime/internal/syscall

This change moves Linux epoll's syscalls implementation to the "runtime/internal/syscall" package. The intention in this CL was to minimise behavioural changes but make the code more generalised. This also will allow adding new syscalls (like epoll_pwait2) without the need to implement assembly stubs for each arch. It also drops epoll_create as not all architectures provide this call. epoll_create1 was added to the kernel in version 2.6.27 and Go requires Linux kernel version 2.6.32 or later since Go 1.18. So it is safe to always use epoll_create1. For #53824 For #51087 Change-Id: I9a6a26b7f2075a38e041de1bab4691da0ecb94fc Reviewed-on: https://go-review.googlesource.com/c/go/+/421994 Reviewed-by: Michael Pratt <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Dmitri Shuralyov <[email protected]> Run-TryBot: Michael Pratt <[email protected]> Auto-Submit: Michael Pratt <[email protected]>

gopherbot · 2022-09-30T18:52:55Z

Change https://go.dev/cl/437295 mentions this issue: Revert "runtime: move epoll syscalls to runtime/internal/syscall"

This reverts CL 421994. Reason for revert: breaks runtime.TestCheckPtr2 For #53824 For #51087 Change-Id: I044ea4d6efdffe0a4b7fb0d2bb3717d9f391fc59 Reviewed-on: https://go-review.googlesource.com/c/go/+/437295 TryBot-Result: Gopher Robot <[email protected]> Run-TryBot: Michael Pratt <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Reviewed-by: Bryan Mills <[email protected]>

gopherbot · 2022-10-07T10:28:22Z

Change https://go.dev/cl/440115 mentions this issue: runtime: move epoll syscalls to runtime/internal/syscall

This change moves Linux epoll's syscalls implementation to the "runtime/internal/syscall" package. The intention in this CL was to minimise behavioural changes but make the code more generalised. This also will allow adding new syscalls (like epoll_pwait2) without the need to implement assembly stubs for each arch. It also drops epoll_create as not all architectures provide this call. epoll_create1 was added to the kernel in version 2.6.27 and Go requires Linux kernel version 2.6.32 or later since Go 1.18. So it is safe to always use epoll_create1. This is a resubmit as the previous CL 421994 was reverted due to test failures after the merge with the master. The issue was fixed in CL 438615 For #53824 For #51087 Change-Id: I1bd0f23a85b4f9b80178c5dd36fd3e95ff4f9648 Reviewed-on: https://go-review.googlesource.com/c/go/+/440115 Reviewed-by: Dmitri Shuralyov <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Reviewed-by: Michael Pratt <[email protected]> Run-TryBot: Michael Pratt <[email protected]>

This change moves Linux epoll's syscalls implementation to the "runtime/internal/syscall" package. The intention in this CL was to minimise behavioural changes but make the code more generalised. This also will allow adding new syscalls (like epoll_pwait2) without the need to implement assembly stubs for each arch. It also drops epoll_create as not all architectures provide this call. epoll_create1 was added to the kernel in version 2.6.27 and Go requires Linux kernel version 2.6.32 or later since Go 1.18. So it is safe to always use epoll_create1. This is a resubmit as the previous CL 421994 was reverted due to test failures after the merge with the master. The issue was fixed in CL 438615 For golang#53824 For golang#51087 Change-Id: I1bd0f23a85b4f9b80178c5dd36fd3e95ff4f9648 Reviewed-on: https://go-review.googlesource.com/c/go/+/440115 Reviewed-by: Dmitri Shuralyov <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Auto-Submit: Michael Pratt <[email protected]> Reviewed-by: Michael Pratt <[email protected]> Run-TryBot: Michael Pratt <[email protected]>

Add Getrandom to internal/runtime/syscall. Use Getrandom instead of reading /dev/urandom to simplify the code. Since Go 1.24 needs Linux kernel >= 3.2, and getrandom(2) was introduced by Linux kernel 3.17, Getrandom could return ENOSYS. This doesn't matter because the Linux kernel always sets startupRand, so readRandom is usually not reachable. We also have a time-based fallback even if readRandom fails. Updates golang#51087 Fixes golang#68278

gopherbot · 2024-09-12T14:24:47Z

Change https://go.dev/cl/612715 mentions this issue: runtime: use getrandom(2) for readRandom on Linux

prattmic added this to the Backlog milestone Feb 8, 2022

cherrymui added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Feb 8, 2022

prattmic added this to Go Compiler / Runtime Feb 24, 2022

prattmic moved this to Todo in Go Compiler / Runtime Feb 24, 2022

prattmic modified the milestones: Backlog, Go1.19 Feb 24, 2022

prattmic mentioned this issue Feb 24, 2022

syscall: add PidFD, CgroupFD, and UseCgroupFD options for Linux clone to SysProcAttr #51246

Closed

prattmic self-assigned this Feb 28, 2022

prattmic moved this from Todo to In Progress in Go Compiler / Runtime Apr 22, 2022

prattmic modified the milestones: Go1.19, Go1.20 Apr 22, 2022

gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 7, 2022

dAdAbird mentioned this issue Jul 29, 2022

runtime: use epoll_pwait2 where available for sub-millisecond timeout precision on Linux #53824

Open

prattmic modified the milestones: Go1.20, Backlog Jan 11, 2023

prattmic mentioned this issue Jan 29, 2024

runtime: move internals to internal/runtime #65355

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apocelipes mentioned this issue Sep 12, 2024

runtime: use getrandom(2) for readRandom on Linux #69421

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runtime: clean up system call code #51087

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runtime: clean up system call code #51087

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