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During a cgocallback, the runtime calls needm to get an m.
The calls made during needm cannot themselves assume that
there is an m or a g (which is attached to the m).
In the old days of making direct system calls, the only thing
you had to do for such functions was mark them //go:nosplit,
to avoid the use of g in the stack split prologue.
But now, on operating systems that make system calls through
shared libraries and use code that saves state in the g or m
before doing so, it's not safe to assume g exists. In fact, it is
not even safe to call getg(), because it might fault deferencing
the TLS storage to find the g pointer (that storage may not be
initialized yet, at least on Windows, and perhaps on other systems
in the future).
The specific routines that are problematic are usleep and osyield,
which are called during lock contention in lockextra, called
from needm.
All this is rather subtle and hidden, so in addition to fixing the
problem on Windows, this CL makes the fact of not running on
a g much clearer by introducing variants usleep_no_g and
osyield_no_g whose names should make clear that there is no g.
And then we can remove the various sketchy getg() == nil checks
in the existing routines.
As part of this cleanup, this CL also deletes onosstack on Windows.
onosstack is from back when the runtime was implemented in C.
It predates systemstack but does essentially the same thing.
Instead of having two different copies of this code, we can use
systemstack consistently. This way we need not port onosstack
to each architecture.
This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.
This CL is, however, not windows/arm64-specific.
It is cleanup meant to make the port (and future ports) easier.
Change-Id: I3352de1fd0a3c26267c6e209063e6e86abd26187
Reviewed-on: https://go-review.googlesource.com/c/go/+/288793
Trust: Russ Cox <rsc@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Working toward making the tree vet-safe instead of having
so many exceptions in cmd/vet/all/whitelist.
This CL makes "GOOS=linux GOARCH=amd64 go vet -unsafeptr=false runtime" happy,
while keeping "GO_BUILDER_NAME=misc-vetall go tool dist test" happy too.
For #31916.
Change-Id: I4ca1acb02f4666b102d25fcc55fac96b8f80379a
Reviewed-on: https://go-review.googlesource.com/c/go/+/176100
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
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Working toward making the tree vet-safe instead of having
so many exceptions in cmd/vet/all/whitelist.
This CL makes "GOOS=linux GOARCH=386 go vet -unsafeptr=false runtime" happy,
while keeping "GO_BUILDER_NAME=misc-vetall go tool dist test" happy too.
For #31916.
Change-Id: I3e5586a7ff6e359357350d0602c2259493280ded
Reviewed-on: https://go-review.googlesource.com/c/go/+/176099
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
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There are three cases where we don't currently have the visibility to
get the ABIs of runtime symbols right, which this CL fixes:
1. For Go functions referenced from non-Go code in other packages.
This is runtime.morestackc (which is referenced from function
prologues) and a few syscall symbols. For these we need to generate
ABI0 wrappers, so this CL adds dummy calls in the assembly code to
force wrapper generation. There are many other cross-package
references to runtime and runtime/internal/atomic, but these are
handled specially by cmd/go.
2. For calls generated by the compiler to runtime Go functions, there
are a few symbols that aren't declared in builtins.go because we've
never needed their type information before. Now we at least need
their ABI information, so these are added to builtins.go.
3. For calls generated by the compiler to runtime assembly functions,
the compiler is going to assume the internal ABI is available, so
we add Go stubs to the runtime to trigger wrapper generation. For
these we're probably going to want to provide internal ABI
definitions directly in the assembly for performance, but for now
the ABIs are the same so it doesn't matter.
For #27539.
Change-Id: I9c224e7408d2ef4dd9b0e4c9d7e962ddfe111245
Reviewed-on: https://go-review.googlesource.com/c/146822
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
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