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491c1e7e95
[This cherry-pick combines CL 527715, CL 527775, CL 527797, and CL 529216.] [This is a redo of CL 525455 with the test fixed on darwin by defining _XOPEN_SOURCE, and disabled with android, musl, and openbsd, which do not provide getcontext.] Since CL 495855, Ms are cached for C threads calling into Go, including the stack bounds of the system stack. Some C libraries (e.g., coroutine libraries) do manual stack management and may change stacks between calls to Go on the same thread. Changing the stack if there is more Go up the stack would be problematic. But if the calls are completely independent there is no particular reason for Go to care about the changing stack boundary. Thus, this CL allows the stack bounds to change in such cases. The primary downside here (besides additional complexity) is that normal systems that do not manipulate the stack may not notice unintentional stack corruption as quickly as before. Note that callbackUpdateSystemStack is written to be usable for the initial setup in needm as well as updating the stack in cgocallbackg. For #62440. For #62130. For #63209. Change-Id: I0fe0134f865932bbaff1fc0da377c35c013bd768 Reviewed-on: https://go-review.googlesource.com/c/go/+/527715 Run-TryBot: Michael Pratt <mpratt@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Auto-Submit: Michael Pratt <mpratt@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com> (cherry picked from commit4f9fe6d509) (cherry picked from commite8ba0579e2) (cherry picked from commita843991fdd) (cherry picked from commitd110d7c42d) Reviewed-on: https://go-review.googlesource.com/c/go/+/530480 Auto-Submit: Dmitri Shuralyov <dmitshur@google.com> TryBot-Bypass: Michael Pratt <mpratt@google.com>
Vendoring in std and cmd
========================
The Go command maintains copies of external packages needed by the
standard library in the src/vendor and src/cmd/vendor directories.
There are two modules, std and cmd, defined in src/go.mod and
src/cmd/go.mod. When a package outside std or cmd is imported
by a package inside std or cmd, the import path is interpreted
as if it had a "vendor/" prefix. For example, within "crypto/tls",
an import of "golang.org/x/crypto/cryptobyte" resolves to
"vendor/golang.org/x/crypto/cryptobyte". When a package with the
same path is imported from a package outside std or cmd, it will
be resolved normally. Consequently, a binary may be built with two
copies of a package at different versions if the package is
imported normally and vendored by the standard library.
Vendored packages are internally renamed with a "vendor/" prefix
to preserve the invariant that all packages have distinct paths.
This is necessary to avoid compiler and linker conflicts. Adding
a "vendor/" prefix also maintains the invariant that standard
library packages begin with a dotless path element.
The module requirements of std and cmd do not influence version
selection in other modules. They are only considered when running
module commands like 'go get' and 'go mod vendor' from a directory
in GOROOT/src.
Maintaining vendor directories
==============================
Before updating vendor directories, ensure that module mode is enabled.
Make sure that GO111MODULE is not set in the environment, or that it is
set to 'on' or 'auto'.
Requirements may be added, updated, and removed with 'go get'.
The vendor directory may be updated with 'go mod vendor'.
A typical sequence might be:
cd src
go get golang.org/x/net@master
go mod tidy
go mod vendor
Use caution when passing '-u' to 'go get'. The '-u' flag updates
modules providing all transitively imported packages, not only
the module providing the target package.
Note that 'go mod vendor' only copies packages that are transitively
imported by packages in the current module. If a new package is needed,
it should be imported before running 'go mod vendor'.