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
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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
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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
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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
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…mplementation on linux

For #51087

Change-Id: I75a1bdeb5089454595f5ca04765a9c6e45cf9bd5
Reviewed-on: https://go-review.googlesource.com/c/go/+/388475
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For #51087

Change-Id: I63e07638507328efe33dbf7dd5f8a8b78890e037
Reviewed-on: https://go-review.googlesource.com/c/go/+/388476
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For #51087

Change-Id: I9de7e85ccf137ae73662759382334bcbe7208150
Reviewed-on: https://go-review.googlesource.com/c/go/+/388477
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For #51087

Change-Id: I4a5b5cb74f12db8999c6ff0e98c3034b58af3959
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For #51087.

Change-Id: I25971760b63ec0d23d0f011521dd197d81a38976
Reviewed-on: https://go-review.googlesource.com/c/go/+/401096
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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
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This reverts CL 388478. Parent CL 388477 breaks cmd/go
TestScript/cover_pkgall_runtime.

For #51087.
For #52472.

Change-Id: Id5d5a4e138792cf130ecdcc6b996c8102d142a7e
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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
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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
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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
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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
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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
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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
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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
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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 <dmitshur@google.com>
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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 <dmitshur@google.com>
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