src/runtime/extern.go - go - Git at Google


            
            // Copyright 2009 The Go Authors. All rights reserved.

            
            // Use of this source code is governed by a BSD-style

            
            // license that can be found in the LICENSE file.


            /*

            
            Package runtime contains operations that interact with Go's runtime system,

            
            such as functions to control goroutines. It also includes the low-level type information

            
            used by the reflect package; see [reflect]'s documentation for the programmable

            
            interface to the run-time type system.


            # Environment Variables


            The following environment variables ($name or %name%, depending on the host

            
            operating system) control the run-time behavior of Go programs. The meanings

            
            and use may change from release to release.


            The GOGC variable sets the initial garbage collection target percentage.

            
            A collection is triggered when the ratio of freshly allocated data to live data

            
            remaining after the previous collection reaches this percentage. The default

            
            is GOGC=100. Setting GOGC=off disables the garbage collector entirely.

            
            [runtime/debug.SetGCPercent] allows changing this percentage at run time.


            The GOMEMLIMIT variable sets a soft memory limit for the runtime. This memory limit

            
            includes the Go heap and all other memory managed by the runtime, and excludes

            
            external memory sources such as mappings of the binary itself, memory managed in

            
            other languages, and memory held by the operating system on behalf of the Go

            
            program. GOMEMLIMIT is a numeric value in bytes with an optional unit suffix.

            
            The supported suffixes include B, KiB, MiB, GiB, and TiB. These suffixes

            
            represent quantities of bytes as defined by the IEC 80000-13 standard. That is,

            
            they are based on powers of two: KiB means 2^10 bytes, MiB means 2^20 bytes,

            
            and so on. The default setting is [math.MaxInt64], which effectively disables the

            
            memory limit. [runtime/debug.SetMemoryLimit] allows changing this limit at run

            
            time.


            The GODEBUG variable controls debugging variables within the runtime.

            
            It is a comma-separated list of name=val pairs setting these named variables:


            	clobberfree: setting clobberfree=1 causes the garbage collector to

            
            	clobber the memory content of an object with bad content when it frees

            
            	the object.


            	cpu.*: cpu.all=off disables the use of all optional instruction set extensions.

            
            	cpu.extension=off disables use of instructions from the specified instruction set extension.

            
            	extension is the lower case name for the instruction set extension such as sse41 or avx

            
            	as listed in internal/cpu package. As an example cpu.avx=off disables runtime detection

            
            	and thereby use of AVX instructions.


            	cgocheck: setting cgocheck=0 disables all checks for packages

            
            	using cgo to incorrectly pass Go pointers to non-Go code.

            
            	Setting cgocheck=1 (the default) enables relatively cheap

            
            	checks that may miss some errors. A more complete, but slow,

            
            	cgocheck mode can be enabled using GOEXPERIMENT (which

            
            	requires a rebuild), see https://pkg.go.dev/internal/goexperiment for details.


            	checkfinalizers: setting checkfinalizers=1 causes the garbage collector to run

            
            	multiple partial non-parallel stop-the-world collections to identify common issues with

            
            	finalizers and cleanups, like those listed at

            
            	https://go.dev/doc/gc-guide#Finalizers_cleanups_and_weak_pointers. If a potential issue

            
            	is found, the program will terminate with a description of all potential issues, the

            
            	associated values, and a list of those values' finalizers and cleanups, including where

            
            	they were created. It also adds tracking for tiny blocks to help diagnose issues with

            
            	those as well. The analysis performed during the partial collection is conservative.

            
            	Notably, it flags any path back to the original object from the cleanup function,

            
            	cleanup arguments, or finalizer function as a potential issue, even if that path might

            
            	be severed sometime later during execution (though this is not a recommended pattern).

            
            	This mode also produces one line of output to stderr every GC cycle with information

            
            	about the finalizer and cleanup queue lengths. Lines produced by this mode start with

            
            	"checkfinalizers:".


            	decoratemappings: controls whether the Go runtime annotates OS

            
            	anonymous memory mappings with context about their purpose. These

            
            	annotations appear in /proc/self/maps and /proc/self/smaps as

            
            	"[anon: Go: ...]". This setting is only used on Linux. For Go 1.25, it

            
            	defaults to `decoratemappings=1`, enabling annotations. Using

            
            	`decoratemappings=0` reverts to the pre-Go 1.25 behavior.


            	disablethp: setting disablethp=1 on Linux disables transparent huge pages for the heap.

            
            	It has no effect on other platforms. disablethp is meant for compatibility with versions

            
            	of Go before 1.21, which stopped working around a Linux kernel default that can result

            
            	in significant memory overuse. See https://go.dev/issue/64332. This setting will be

            
            	removed in a future release, so operators should tweak their Linux configuration to suit

            
            	their needs before then. See https://go.dev/doc/gc-guide#Linux_transparent_huge_pages.


            	dontfreezetheworld: by default, the start of a fatal panic or throw

            
            	"freezes the world", preempting all threads to stop all running

            
            	goroutines, which makes it possible to traceback all goroutines, and

            
            	keeps their state close to the point of panic. Setting

            
            	dontfreezetheworld=1 disables this preemption, allowing goroutines to

            
            	continue executing during panic processing. Note that goroutines that

            
            	naturally enter the scheduler will still stop. This can be useful when

            
            	debugging the runtime scheduler, as freezetheworld perturbs scheduler

            
            	state and thus may hide problems.


            	efence: setting efence=1 causes the allocator to run in a mode

            
            	where each object is allocated on a unique page and addresses are

            
            	never recycled.


            	gccheckmark: setting gccheckmark=1 enables verification of the

            
            	garbage collector's concurrent mark phase by performing a

            
            	second mark pass while the world is stopped.  If the second

            
            	pass finds a reachable object that was not found by concurrent

            
            	mark, the garbage collector will panic.


            	gcpacertrace: setting gcpacertrace=1 causes the garbage collector to

            
            	print information about the internal state of the concurrent pacer.


            	gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines

            
            	onto smaller stacks. In this mode, a goroutine's stack can only grow.


            	gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,

            
            	making every garbage collection a stop-the-world event. Setting gcstoptheworld=2

            
            	also disables concurrent sweeping after the garbage collection finishes.


            	gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard

            
            	error at each collection, summarizing the amount of memory collected and the

            
            	length of the pause. The format of this line is subject to change. Included in

            
            	the explanation below is also the relevant runtime/metrics metric for each field.

            
            	Currently, it is:

            
            		gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # MB stacks, #MB globals, # P

            
            	where the fields are as follows:

            
            		gc #         the GC number, incremented at each GC

            
            		@#s          time in seconds since program start

            
            		#%           percentage of time spent in GC since program start

            
            		#+...+#      wall-clock/CPU times for the phases of the GC

            
            		#->#-># MB   heap size at GC start, at GC end, and live heap, or /gc/scan/heap:bytes

            
            		# MB goal    goal heap size, or /gc/heap/goal:bytes

            
            		# MB stacks  estimated scannable stack size, or /gc/scan/stack:bytes

            
            		# MB globals scannable global size, or /gc/scan/globals:bytes

            
            		# P          number of processors used, or /sched/gomaxprocs:threads

            
            	The phases are stop-the-world (STW) sweep termination, concurrent

            
            	mark and scan, and STW mark termination. The CPU times

            
            	for mark/scan are broken down in to assist time (GC performed in

            
            	line with allocation), background GC time, and idle GC time.

            
            	If the line ends with "(forced)", this GC was forced by a

            
            	runtime.GC() call.


            	harddecommit: setting harddecommit=1 causes memory that is returned to the OS to

            
            	also have protections removed on it. This is the only mode of operation on Windows,

            
            	but is helpful in debugging scavenger-related issues on other platforms. Currently,

            
            	only supported on Linux.


            	inittrace: setting inittrace=1 causes the runtime to emit a single line to standard

            
            	error for each package with init work, summarizing the execution time and memory

            
            	allocation. No information is printed for inits executed as part of plugin loading

            
            	and for packages without both user defined and compiler generated init work.

            
            	The format of this line is subject to change. Currently, it is:

            
            		init # @#ms, # ms clock, # bytes, # allocs

            
            	where the fields are as follows:

            
            		init #      the package name

            
            		@# ms       time in milliseconds when the init started since program start

            
            		# clock     wall-clock time for package initialization work

            
            		# bytes     memory allocated on the heap

            
            		# allocs    number of heap allocations


            	madvdontneed: setting madvdontneed=0 will use MADV_FREE

            
            	instead of MADV_DONTNEED on Linux when returning memory to the

            
            	kernel. This is more efficient, but means RSS numbers will

            
            	drop only when the OS is under memory pressure. On the BSDs and

            
            	Illumos/Solaris, setting madvdontneed=1 will use MADV_DONTNEED instead

            
            	of MADV_FREE. This is less efficient, but causes RSS numbers to drop

            
            	more quickly.


            	memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.

            
            	When set to 0 memory profiling is disabled.  Refer to the description of

            
            	MemProfileRate for the default value.


            	profstackdepth: profstackdepth=128 (the default) will set the maximum stack

            
            	depth used by all pprof profilers except for the CPU profiler to 128 frames.

            
            	Stack traces that exceed this limit will be truncated to the limit starting

            
            	from the leaf frame. Setting profstackdepth to any value above 1024 will

            
            	silently default to 1024. Future versions of Go may remove this limitation

            
            	and extend profstackdepth to apply to the CPU profiler and execution tracer.


            	panicnil: setting panicnil=1 disables the runtime error when calling panic with nil

            
            	interface value or an untyped nil.


            	invalidptr: invalidptr=1 (the default) causes the garbage collector and stack

            
            	copier to crash the program if an invalid pointer value (for example, 1)

            
            	is found in a pointer-typed location. Setting invalidptr=0 disables this check.

            
            	This should only be used as a temporary workaround to diagnose buggy code.

            
            	The real fix is to not store integers in pointer-typed locations.


            	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector

            
            	with a trivial allocator that obtains memory from the operating system and

            
            	never reclaims any memory.


            	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard

            
            	error, roughly once per GC cycle, summarizing the amount of work done by the

            
            	scavenger as well as the total amount of memory returned to the operating system

            
            	and an estimate of physical memory utilization. The format of this line is subject

            
            	to change, but currently it is:

            
            		scav # KiB work (bg), # KiB work (eager), # KiB total, #% util

            
            	where the fields are as follows:

            
            		# KiB work (bg)    the amount of memory returned to the OS in the background since

            
            		                   the last line

            
            		# KiB work (eager) the amount of memory returned to the OS eagerly since the last line

            
            		# KiB now          the amount of address space currently returned to the OS

            
            		#% util            the fraction of all unscavenged heap memory which is in-use

            
            	If the line ends with "(forced)", then scavenging was forced by a

            
            	debug.FreeOSMemory() call.


            	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit

            
            	detailed multiline info every X milliseconds, describing state of the scheduler,

            
            	processors, threads and goroutines.


            	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard

            
            	error every X milliseconds, summarizing the scheduler state.


            	tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at

            
            	which goroutines were created, where N limits the number of ancestor goroutines to

            
            	report. This also extends the information returned by runtime.Stack.

            
            	Setting N to 0 will report no ancestry information.


            	tracebackcrash: setting tracebackcrash=1 causes the runtime to throw a fatal

            
            	error on any unwinding error, even for unwinds such as CPU profiling that

            
            	otherwise tolerate errors and report a truncated stack.


            	tracefpunwindoff: setting tracefpunwindoff=1 forces the execution tracer

            
            	and block and mutex profilers to use the runtime's default stack

            
            	unwinder instead of frame pointer unwinding. This increases their

            
            	overhead, but could be helpful as a workaround or for debugging

            
            	unexpected regressions caused by frame pointer unwinding.


            	traceadvanceperiod: the approximate period in nanoseconds between trace generations. Only

            
            	applies if a program is built with GOEXPERIMENT=exectracer2. Used primarily for testing

            
            	and debugging the execution tracer.


            	tracecheckstackownership: setting tracecheckstackownership=1 enables a debug check in the

            
            	execution tracer to double-check stack ownership before taking a stack trace.


            	asyncpreemptoff: asyncpreemptoff=1 disables signal-based

            
            	asynchronous goroutine preemption. This makes some loops

            
            	non-preemptible for long periods, which may delay GC and

            
            	goroutine scheduling. This is useful for debugging GC issues

            
            	because it also disables the conservative stack scanning used

            
            	for asynchronously preempted goroutines.


            The [net] and [net/http] packages also refer to debugging variables in GODEBUG.

            
            See the documentation for those packages for details.


            The GOMAXPROCS variable limits the number of operating system threads that

            
            can execute user-level Go code simultaneously. There is no limit to the number of threads

            
            that can be blocked in system calls on behalf of Go code; those do not count against

            
            the GOMAXPROCS limit. This package's [GOMAXPROCS] function queries and changes

            
            the limit.


            The GORACE variable configures the race detector, for programs built using -race.

            
            See the [Race Detector article] for details.


            The GOTRACEBACK variable controls the amount of output generated when a Go

            
            program fails due to an unrecovered panic or an unexpected runtime condition.

            
            By default, a failure prints a stack trace for the current goroutine,

            
            eliding functions internal to the run-time system, and then exits with exit code 2.

            
            The failure prints stack traces for all goroutines if there is no current goroutine

            
            or the failure is internal to the run-time.

            
            GOTRACEBACK=none omits the goroutine stack traces entirely.

            
            GOTRACEBACK=single (the default) behaves as described above.

            
            GOTRACEBACK=all adds stack traces for all user-created goroutines.

            
            GOTRACEBACK=system is like “all” but adds stack frames for run-time functions

            
            and shows goroutines created internally by the run-time.

            
            GOTRACEBACK=crash is like “system” but crashes in an operating system-specific

            
            manner instead of exiting. For example, on Unix systems, the crash raises

            
            SIGABRT to trigger a core dump.

            
            GOTRACEBACK=wer is like “crash” but doesn't disable Windows Error Reporting (WER).

            
            For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for

            
            none, all, and system, respectively.

            
            The [runtime/debug.SetTraceback] function allows increasing the

            
            amount of output at run time, but it cannot reduce the amount below that

            
            specified by the environment variable.


            The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete

            
            the set of Go environment variables. They influence the building of Go programs

            
            (see [cmd/go] and [go/build]).

            
            GOARCH, GOOS, and GOROOT are recorded at compile time and made available by

            
            constants or functions in this package, but they do not influence the execution

            
            of the run-time system.


            # Security


            On Unix platforms, Go's runtime system behaves slightly differently when a

            
            binary is setuid/setgid or executed with setuid/setgid-like properties, in order

            
            to prevent dangerous behaviors. On Linux this is determined by checking for the

            
            AT_SECURE flag in the auxiliary vector, on the BSDs and Solaris/Illumos it is

            
            determined by checking the issetugid syscall, and on AIX it is determined by

            
            checking if the uid/gid match the effective uid/gid.


            When the runtime determines the binary is setuid/setgid-like, it does two main

            
            things:

            
              - The value of the GOTRACEBACK environment variable is set to 'none'.

            
              - When a signal is received that terminates the program, or the program

            
                encounters an unrecoverable panic that would otherwise override the value

            
                of GOTRACEBACK, the goroutine stack, registers, and other memory related

            
                information are omitted.


            Additinally on Unix platforms the Go runtime automatically checks whether

            
            the standard input/output file descriptors (0, 1, 2) are open. If any of them are

            
            closed, they are opened pointing at /dev/null.


            [Race Detector article]: https://go.dev/doc/articles/race_detector

            
            */

            
            package runtime


            import (

            
            	"internal/goarch"

            
            	"internal/goos"

            
            )


            // Caller reports file and line number information about function invocations on

            
            // the calling goroutine's stack. The argument skip is the number of stack frames

            
            // to ascend, with 0 identifying the caller of Caller. (For historical reasons the

            
            // meaning of skip differs between Caller and [Callers].) The return values report

            
            // the program counter, the file name (using forward slashes as path separator, even

            
            // on Windows), and the line number within the file of the corresponding call.

            
            // The boolean ok is false if it was not possible to recover the information.

            
            func Caller(skip int) (pc uintptr, file string, line int, ok bool) {

            
            	rpc := make([]uintptr, 1)

            
            	n := callers(skip+1, rpc)

            
            	if n < 1 {

            
            		return

            
            	}

            
            	frame, _ := CallersFrames(rpc).Next()

            
            	return frame.PC, frame.File, frame.Line, frame.PC != 0

            
            }


            // Callers fills the slice pc with the return program counters of function invocations

            
            // on the calling goroutine's stack. The argument skip is the number of stack frames

            
            // to skip before recording in pc, with 0 identifying the frame for Callers itself and

            
            // 1 identifying the caller of Callers.

            
            // It returns the number of entries written to pc.

            
            //

            
            // To translate these PCs into symbolic information such as function

            
            // names and line numbers, use [CallersFrames]. CallersFrames accounts

            
            // for inlined functions and adjusts the return program counters into

            
            // call program counters. Iterating over the returned slice of PCs

            
            // directly is discouraged, as is using [FuncForPC] on any of the

            
            // returned PCs, since these cannot account for inlining or return

            
            // program counter adjustment.

            
            func Callers(skip int, pc []uintptr) int {

            
            	// runtime.callers uses pc.array==nil as a signal

            
            	// to print a stack trace. Pick off 0-length pc here

            
            	// so that we don't let a nil pc slice get to it.

            
            	if len(pc) == 0 {

            
            		return 0

            
            	}

            
            	return callers(skip, pc)

            
            }


            var defaultGOROOT string // set by cmd/link


            // GOROOT returns the root of the Go tree. It uses the

            
            // GOROOT environment variable, if set at process start,

            
            // or else the root used during the Go build.

            
            //

            
            // Deprecated: The root used during the Go build will not be

            
            // meaningful if the binary is copied to another machine.

            
            // Use the system path to locate the “go” binary, and use

            
            // “go env GOROOT” to find its GOROOT.

            
            func GOROOT() string {

            
            	s := gogetenv("GOROOT")

            
            	if s != "" {

            
            		return s

            
            	}

            
            	return defaultGOROOT

            
            }


            // buildVersion is the Go tree's version string at build time.

            
            //

            
            // If any GOEXPERIMENTs are set to non-default values, it will include

            
            // "X:<GOEXPERIMENT>".

            
            //

            
            // This is set by the linker.

            
            //

            
            // This is accessed by "go version <binary>".

            
            var buildVersion string


            // Version returns the Go tree's version string.

            
            // It is either the commit hash and date at the time of the build or,

            
            // when possible, a release tag like "go1.3".

            
            func Version() string {

            
            	return buildVersion

            
            }


            // GOOS is the running program's operating system target:

            
            // one of darwin, freebsd, linux, and so on.

            
            // To view possible combinations of GOOS and GOARCH, run "go tool dist list".

            
            const GOOS string = goos.GOOS


            // GOARCH is the running program's architecture target:

            
            // one of 386, amd64, arm, s390x, and so on.

            
            const GOARCH string = goarch.GOARCH
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	/*
	Package runtime contains operations that interact with Go's runtime system,
	such as functions to control goroutines. It also includes the low-level type information
	used by the reflect package; see [reflect]'s documentation for the programmable
	interface to the run-time type system.

	# Environment Variables

	The following environment variables ($name or %name%, depending on the host
	operating system) control the run-time behavior of Go programs. The meanings
	and use may change from release to release.

	The GOGC variable sets the initial garbage collection target percentage.
	A collection is triggered when the ratio of freshly allocated data to live data
	remaining after the previous collection reaches this percentage. The default
	is GOGC=100. Setting GOGC=off disables the garbage collector entirely.
	[runtime/debug.SetGCPercent] allows changing this percentage at run time.

	The GOMEMLIMIT variable sets a soft memory limit for the runtime. This memory limit
	includes the Go heap and all other memory managed by the runtime, and excludes
	external memory sources such as mappings of the binary itself, memory managed in
	other languages, and memory held by the operating system on behalf of the Go
	program. GOMEMLIMIT is a numeric value in bytes with an optional unit suffix.
	The supported suffixes include B, KiB, MiB, GiB, and TiB. These suffixes
	represent quantities of bytes as defined by the IEC 80000-13 standard. That is,
	they are based on powers of two: KiB means 2^10 bytes, MiB means 2^20 bytes,
	and so on. The default setting is [math.MaxInt64], which effectively disables the
	memory limit. [runtime/debug.SetMemoryLimit] allows changing this limit at run
	time.

	The GODEBUG variable controls debugging variables within the runtime.
	It is a comma-separated list of name=val pairs setting these named variables:

	clobberfree: setting clobberfree=1 causes the garbage collector to
	clobber the memory content of an object with bad content when it frees
	the object.

	cpu.*: cpu.all=off disables the use of all optional instruction set extensions.
	cpu.extension=off disables use of instructions from the specified instruction set extension.
	extension is the lower case name for the instruction set extension such as sse41 or avx
	as listed in internal/cpu package. As an example cpu.avx=off disables runtime detection
	and thereby use of AVX instructions.

	cgocheck: setting cgocheck=0 disables all checks for packages
	using cgo to incorrectly pass Go pointers to non-Go code.
	Setting cgocheck=1 (the default) enables relatively cheap
	checks that may miss some errors. A more complete, but slow,
	cgocheck mode can be enabled using GOEXPERIMENT (which
	requires a rebuild), see https://pkg.go.dev/internal/goexperiment for details.

	checkfinalizers: setting checkfinalizers=1 causes the garbage collector to run
	multiple partial non-parallel stop-the-world collections to identify common issues with
	finalizers and cleanups, like those listed at
	https://go.dev/doc/gc-guide#Finalizers_cleanups_and_weak_pointers. If a potential issue
	is found, the program will terminate with a description of all potential issues, the
	associated values, and a list of those values' finalizers and cleanups, including where
	they were created. It also adds tracking for tiny blocks to help diagnose issues with
	those as well. The analysis performed during the partial collection is conservative.
	Notably, it flags any path back to the original object from the cleanup function,
	cleanup arguments, or finalizer function as a potential issue, even if that path might
	be severed sometime later during execution (though this is not a recommended pattern).
	This mode also produces one line of output to stderr every GC cycle with information
	about the finalizer and cleanup queue lengths. Lines produced by this mode start with
	"checkfinalizers:".

	decoratemappings: controls whether the Go runtime annotates OS
	anonymous memory mappings with context about their purpose. These
	annotations appear in /proc/self/maps and /proc/self/smaps as
	"[anon: Go: ...]". This setting is only used on Linux. For Go 1.25, it
	defaults to `decoratemappings=1`, enabling annotations. Using
	`decoratemappings=0` reverts to the pre-Go 1.25 behavior.

	disablethp: setting disablethp=1 on Linux disables transparent huge pages for the heap.
	It has no effect on other platforms. disablethp is meant for compatibility with versions
	of Go before 1.21, which stopped working around a Linux kernel default that can result
	in significant memory overuse. See https://go.dev/issue/64332. This setting will be
	removed in a future release, so operators should tweak their Linux configuration to suit
	their needs before then. See https://go.dev/doc/gc-guide#Linux_transparent_huge_pages.

	dontfreezetheworld: by default, the start of a fatal panic or throw
	"freezes the world", preempting all threads to stop all running
	goroutines, which makes it possible to traceback all goroutines, and
	keeps their state close to the point of panic. Setting
	dontfreezetheworld=1 disables this preemption, allowing goroutines to
	continue executing during panic processing. Note that goroutines that
	naturally enter the scheduler will still stop. This can be useful when
	debugging the runtime scheduler, as freezetheworld perturbs scheduler
	state and thus may hide problems.

	efence: setting efence=1 causes the allocator to run in a mode
	where each object is allocated on a unique page and addresses are
	never recycled.

	gccheckmark: setting gccheckmark=1 enables verification of the
	garbage collector's concurrent mark phase by performing a
	second mark pass while the world is stopped. If the second
	pass finds a reachable object that was not found by concurrent
	mark, the garbage collector will panic.

	gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
	print information about the internal state of the concurrent pacer.

	gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
	onto smaller stacks. In this mode, a goroutine's stack can only grow.

	gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
	making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
	also disables concurrent sweeping after the garbage collection finishes.

	gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard
	error at each collection, summarizing the amount of memory collected and the
	length of the pause. The format of this line is subject to change. Included in
	the explanation below is also the relevant runtime/metrics metric for each field.
	Currently, it is:
	gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # MB stacks, #MB globals, # P
	where the fields are as follows:
	gc # the GC number, incremented at each GC
	@#s time in seconds since program start
	#% percentage of time spent in GC since program start
	#+...+# wall-clock/CPU times for the phases of the GC
	#->#-># MB heap size at GC start, at GC end, and live heap, or /gc/scan/heap:bytes
	# MB goal goal heap size, or /gc/heap/goal:bytes
	# MB stacks estimated scannable stack size, or /gc/scan/stack:bytes
	# MB globals scannable global size, or /gc/scan/globals:bytes
	# P number of processors used, or /sched/gomaxprocs:threads
	The phases are stop-the-world (STW) sweep termination, concurrent
	mark and scan, and STW mark termination. The CPU times
	for mark/scan are broken down in to assist time (GC performed in
	line with allocation), background GC time, and idle GC time.
	If the line ends with "(forced)", this GC was forced by a
	runtime.GC() call.

	harddecommit: setting harddecommit=1 causes memory that is returned to the OS to
	also have protections removed on it. This is the only mode of operation on Windows,
	but is helpful in debugging scavenger-related issues on other platforms. Currently,
	only supported on Linux.

	inittrace: setting inittrace=1 causes the runtime to emit a single line to standard
	error for each package with init work, summarizing the execution time and memory
	allocation. No information is printed for inits executed as part of plugin loading
	and for packages without both user defined and compiler generated init work.
	The format of this line is subject to change. Currently, it is:
	init # @#ms, # ms clock, # bytes, # allocs
	where the fields are as follows:
	init # the package name
	@# ms time in milliseconds when the init started since program start
	# clock wall-clock time for package initialization work
	# bytes memory allocated on the heap
	# allocs number of heap allocations

	madvdontneed: setting madvdontneed=0 will use MADV_FREE
	instead of MADV_DONTNEED on Linux when returning memory to the
	kernel. This is more efficient, but means RSS numbers will
	drop only when the OS is under memory pressure. On the BSDs and
	Illumos/Solaris, setting madvdontneed=1 will use MADV_DONTNEED instead
	of MADV_FREE. This is less efficient, but causes RSS numbers to drop
	more quickly.

	memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
	When set to 0 memory profiling is disabled. Refer to the description of
	MemProfileRate for the default value.

	profstackdepth: profstackdepth=128 (the default) will set the maximum stack
	depth used by all pprof profilers except for the CPU profiler to 128 frames.
	Stack traces that exceed this limit will be truncated to the limit starting
	from the leaf frame. Setting profstackdepth to any value above 1024 will
	silently default to 1024. Future versions of Go may remove this limitation
	and extend profstackdepth to apply to the CPU profiler and execution tracer.

	panicnil: setting panicnil=1 disables the runtime error when calling panic with nil
	interface value or an untyped nil.

	invalidptr: invalidptr=1 (the default) causes the garbage collector and stack
	copier to crash the program if an invalid pointer value (for example, 1)
	is found in a pointer-typed location. Setting invalidptr=0 disables this check.
	This should only be used as a temporary workaround to diagnose buggy code.
	The real fix is to not store integers in pointer-typed locations.

	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
	with a trivial allocator that obtains memory from the operating system and
	never reclaims any memory.

	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
	error, roughly once per GC cycle, summarizing the amount of work done by the
	scavenger as well as the total amount of memory returned to the operating system
	and an estimate of physical memory utilization. The format of this line is subject
	to change, but currently it is:
	scav # KiB work (bg), # KiB work (eager), # KiB total, #% util
	where the fields are as follows:
	# KiB work (bg) the amount of memory returned to the OS in the background since
	the last line
	# KiB work (eager) the amount of memory returned to the OS eagerly since the last line
	# KiB now the amount of address space currently returned to the OS
	#% util the fraction of all unscavenged heap memory which is in-use
	If the line ends with "(forced)", then scavenging was forced by a
	debug.FreeOSMemory() call.

	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
	detailed multiline info every X milliseconds, describing state of the scheduler,
	processors, threads and goroutines.

	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
	error every X milliseconds, summarizing the scheduler state.

	tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
	which goroutines were created, where N limits the number of ancestor goroutines to
	report. This also extends the information returned by runtime.Stack.
	Setting N to 0 will report no ancestry information.

	tracebackcrash: setting tracebackcrash=1 causes the runtime to throw a fatal
	error on any unwinding error, even for unwinds such as CPU profiling that
	otherwise tolerate errors and report a truncated stack.

	tracefpunwindoff: setting tracefpunwindoff=1 forces the execution tracer
	and block and mutex profilers to use the runtime's default stack
	unwinder instead of frame pointer unwinding. This increases their
	overhead, but could be helpful as a workaround or for debugging
	unexpected regressions caused by frame pointer unwinding.

	traceadvanceperiod: the approximate period in nanoseconds between trace generations. Only
	applies if a program is built with GOEXPERIMENT=exectracer2. Used primarily for testing
	and debugging the execution tracer.

	tracecheckstackownership: setting tracecheckstackownership=1 enables a debug check in the
	execution tracer to double-check stack ownership before taking a stack trace.

	asyncpreemptoff: asyncpreemptoff=1 disables signal-based
	asynchronous goroutine preemption. This makes some loops
	non-preemptible for long periods, which may delay GC and
	goroutine scheduling. This is useful for debugging GC issues
	because it also disables the conservative stack scanning used
	for asynchronously preempted goroutines.

	The [net] and [net/http] packages also refer to debugging variables in GODEBUG.
	See the documentation for those packages for details.

	The GOMAXPROCS variable limits the number of operating system threads that
	can execute user-level Go code simultaneously. There is no limit to the number of threads
	that can be blocked in system calls on behalf of Go code; those do not count against
	the GOMAXPROCS limit. This package's [GOMAXPROCS] function queries and changes
	the limit.

	The GORACE variable configures the race detector, for programs built using -race.
	See the [Race Detector article] for details.

	The GOTRACEBACK variable controls the amount of output generated when a Go
	program fails due to an unrecovered panic or an unexpected runtime condition.
	By default, a failure prints a stack trace for the current goroutine,
	eliding functions internal to the run-time system, and then exits with exit code 2.
	The failure prints stack traces for all goroutines if there is no current goroutine
	or the failure is internal to the run-time.
	GOTRACEBACK=none omits the goroutine stack traces entirely.
	GOTRACEBACK=single (the default) behaves as described above.
	GOTRACEBACK=all adds stack traces for all user-created goroutines.
	GOTRACEBACK=system is like “all” but adds stack frames for run-time functions
	and shows goroutines created internally by the run-time.
	GOTRACEBACK=crash is like “system” but crashes in an operating system-specific
	manner instead of exiting. For example, on Unix systems, the crash raises
	SIGABRT to trigger a core dump.
	GOTRACEBACK=wer is like “crash” but doesn't disable Windows Error Reporting (WER).
	For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
	none, all, and system, respectively.
	The [runtime/debug.SetTraceback] function allows increasing the
	amount of output at run time, but it cannot reduce the amount below that
	specified by the environment variable.

	The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
	the set of Go environment variables. They influence the building of Go programs
	(see [cmd/go] and [go/build]).
	GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
	constants or functions in this package, but they do not influence the execution
	of the run-time system.

	# Security

	On Unix platforms, Go's runtime system behaves slightly differently when a
	binary is setuid/setgid or executed with setuid/setgid-like properties, in order
	to prevent dangerous behaviors. On Linux this is determined by checking for the
	AT_SECURE flag in the auxiliary vector, on the BSDs and Solaris/Illumos it is
	determined by checking the issetugid syscall, and on AIX it is determined by
	checking if the uid/gid match the effective uid/gid.

	When the runtime determines the binary is setuid/setgid-like, it does two main
	things:
	- The value of the GOTRACEBACK environment variable is set to 'none'.
	- When a signal is received that terminates the program, or the program
	encounters an unrecoverable panic that would otherwise override the value
	of GOTRACEBACK, the goroutine stack, registers, and other memory related
	information are omitted.

	Additinally on Unix platforms the Go runtime automatically checks whether
	the standard input/output file descriptors (0, 1, 2) are open. If any of them are
	closed, they are opened pointing at /dev/null.

	[Race Detector article]: https://go.dev/doc/articles/race_detector
	*/
	package runtime

	import (
	"internal/goarch"
	"internal/goos"
	)

	// Caller reports file and line number information about function invocations on
	// the calling goroutine's stack. The argument skip is the number of stack frames
	// to ascend, with 0 identifying the caller of Caller. (For historical reasons the
	// meaning of skip differs between Caller and [Callers].) The return values report
	// the program counter, the file name (using forward slashes as path separator, even
	// on Windows), and the line number within the file of the corresponding call.
	// The boolean ok is false if it was not possible to recover the information.
	func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
	rpc := make([]uintptr, 1)
	n := callers(skip+1, rpc)
	if n < 1 {
	return
	}
	frame, _ := CallersFrames(rpc).Next()
	return frame.PC, frame.File, frame.Line, frame.PC != 0
	}

	// Callers fills the slice pc with the return program counters of function invocations
	// on the calling goroutine's stack. The argument skip is the number of stack frames
	// to skip before recording in pc, with 0 identifying the frame for Callers itself and
	// 1 identifying the caller of Callers.
	// It returns the number of entries written to pc.
	//
	// To translate these PCs into symbolic information such as function
	// names and line numbers, use [CallersFrames]. CallersFrames accounts
	// for inlined functions and adjusts the return program counters into
	// call program counters. Iterating over the returned slice of PCs
	// directly is discouraged, as is using [FuncForPC] on any of the
	// returned PCs, since these cannot account for inlining or return
	// program counter adjustment.
	func Callers(skip int, pc []uintptr) int {
	// runtime.callers uses pc.array==nil as a signal
	// to print a stack trace. Pick off 0-length pc here
	// so that we don't let a nil pc slice get to it.
	if len(pc) == 0 {
	return 0
	}
	return callers(skip, pc)
	}

	var defaultGOROOT string // set by cmd/link

	// GOROOT returns the root of the Go tree. It uses the
	// GOROOT environment variable, if set at process start,
	// or else the root used during the Go build.
	//
	// Deprecated: The root used during the Go build will not be
	// meaningful if the binary is copied to another machine.
	// Use the system path to locate the “go” binary, and use
	// “go env GOROOT” to find its GOROOT.
	func GOROOT() string {
	s := gogetenv("GOROOT")
	if s != "" {
	return s
	}
	return defaultGOROOT
	}

	// buildVersion is the Go tree's version string at build time.
	//
	// If any GOEXPERIMENTs are set to non-default values, it will include
	// "X:<GOEXPERIMENT>".
	//
	// This is set by the linker.
	//
	// This is accessed by "go version <binary>".
	var buildVersion string

	// Version returns the Go tree's version string.
	// It is either the commit hash and date at the time of the build or,
	// when possible, a release tag like "go1.3".
	func Version() string {
	return buildVersion
	}

	// GOOS is the running program's operating system target:
	// one of darwin, freebsd, linux, and so on.
	// To view possible combinations of GOOS and GOARCH, run "go tool dist list".
	const GOOS string = goos.GOOS

	// GOARCH is the running program's architecture target:
	// one of 386, amd64, arm, s390x, and so on.
	const GOARCH string = goarch.GOARCH