Source file src/runtime/extern.go
1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 /* 6 Package runtime contains operations that interact with Go's runtime system, 7 such as functions to control goroutines. It also includes the low-level type information 8 used by the reflect package; see reflect's documentation for the programmable 9 interface to the run-time type system. 10 11 # Environment Variables 12 13 The following environment variables ($name or %name%, depending on the host 14 operating system) control the run-time behavior of Go programs. The meanings 15 and use may change from release to release. 16 17 The GOGC variable sets the initial garbage collection target percentage. 18 A collection is triggered when the ratio of freshly allocated data to live data 19 remaining after the previous collection reaches this percentage. The default 20 is GOGC=100. Setting GOGC=off disables the garbage collector entirely. 21 [runtime/debug.SetGCPercent] allows changing this percentage at run time. 22 23 The GOMEMLIMIT variable sets a soft memory limit for the runtime. This memory limit 24 includes the Go heap and all other memory managed by the runtime, and excludes 25 external memory sources such as mappings of the binary itself, memory managed in 26 other languages, and memory held by the operating system on behalf of the Go 27 program. GOMEMLIMIT is a numeric value in bytes with an optional unit suffix. 28 The supported suffixes include B, KiB, MiB, GiB, and TiB. These suffixes 29 represent quantities of bytes as defined by the IEC 80000-13 standard. That is, 30 they are based on powers of two: KiB means 2^10 bytes, MiB means 2^20 bytes, 31 and so on. The default setting is math.MaxInt64, which effectively disables the 32 memory limit. [runtime/debug.SetMemoryLimit] allows changing this limit at run 33 time. 34 35 The GODEBUG variable controls debugging variables within the runtime. 36 It is a comma-separated list of name=val pairs setting these named variables: 37 38 allocfreetrace: setting allocfreetrace=1 causes every allocation to be 39 profiled and a stack trace printed on each object's allocation and free. 40 41 clobberfree: setting clobberfree=1 causes the garbage collector to 42 clobber the memory content of an object with bad content when it frees 43 the object. 44 45 cpu.*: cpu.all=off disables the use of all optional instruction set extensions. 46 cpu.extension=off disables use of instructions from the specified instruction set extension. 47 extension is the lower case name for the instruction set extension such as sse41 or avx 48 as listed in internal/cpu package. As an example cpu.avx=off disables runtime detection 49 and thereby use of AVX instructions. 50 51 cgocheck: setting cgocheck=0 disables all checks for packages 52 using cgo to incorrectly pass Go pointers to non-Go code. 53 Setting cgocheck=1 (the default) enables relatively cheap 54 checks that may miss some errors. A more complete, but slow, 55 cgocheck mode can be enabled using GOEXPERIMENT (which 56 requires a rebuild), see https://pkg.go.dev/internal/goexperiment for details. 57 58 dontfreezetheworld: by default, the start of a fatal panic or throw 59 "freezes the world", preempting all threads to stop all running 60 goroutines, which makes it possible to traceback all goroutines, and 61 keeps their state close to the point of panic. Setting 62 dontfreezetheworld=1 disables this preemption, allowing goroutines to 63 continue executing during panic processing. Note that goroutines that 64 naturally enter the scheduler will still stop. This can be useful when 65 debugging the runtime scheduler, as freezetheworld perturbs scheduler 66 state and thus may hide problems. 67 68 efence: setting efence=1 causes the allocator to run in a mode 69 where each object is allocated on a unique page and addresses are 70 never recycled. 71 72 gccheckmark: setting gccheckmark=1 enables verification of the 73 garbage collector's concurrent mark phase by performing a 74 second mark pass while the world is stopped. If the second 75 pass finds a reachable object that was not found by concurrent 76 mark, the garbage collector will panic. 77 78 gcpacertrace: setting gcpacertrace=1 causes the garbage collector to 79 print information about the internal state of the concurrent pacer. 80 81 gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines 82 onto smaller stacks. In this mode, a goroutine's stack can only grow. 83 84 gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection, 85 making every garbage collection a stop-the-world event. Setting gcstoptheworld=2 86 also disables concurrent sweeping after the garbage collection finishes. 87 88 gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard 89 error at each collection, summarizing the amount of memory collected and the 90 length of the pause. The format of this line is subject to change. Included in 91 the explanation below is also the relevant runtime/metrics metric for each field. 92 Currently, it is: 93 gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # MB stacks, #MB globals, # P 94 where the fields are as follows: 95 gc # the GC number, incremented at each GC 96 @#s time in seconds since program start 97 #% percentage of time spent in GC since program start 98 #+...+# wall-clock/CPU times for the phases of the GC 99 #->#-># MB heap size at GC start, at GC end, and live heap, or /gc/scan/heap:bytes 100 # MB goal goal heap size, or /gc/heap/goal:bytes 101 # MB stacks estimated scannable stack size, or /gc/scan/stack:bytes 102 # MB globals scannable global size, or /gc/scan/globals:bytes 103 # P number of processors used, or /sched/gomaxprocs:threads 104 The phases are stop-the-world (STW) sweep termination, concurrent 105 mark and scan, and STW mark termination. The CPU times 106 for mark/scan are broken down in to assist time (GC performed in 107 line with allocation), background GC time, and idle GC time. 108 If the line ends with "(forced)", this GC was forced by a 109 runtime.GC() call. 110 111 harddecommit: setting harddecommit=1 causes memory that is returned to the OS to 112 also have protections removed on it. This is the only mode of operation on Windows, 113 but is helpful in debugging scavenger-related issues on other platforms. Currently, 114 only supported on Linux. 115 116 inittrace: setting inittrace=1 causes the runtime to emit a single line to standard 117 error for each package with init work, summarizing the execution time and memory 118 allocation. No information is printed for inits executed as part of plugin loading 119 and for packages without both user defined and compiler generated init work. 120 The format of this line is subject to change. Currently, it is: 121 init # @#ms, # ms clock, # bytes, # allocs 122 where the fields are as follows: 123 init # the package name 124 @# ms time in milliseconds when the init started since program start 125 # clock wall-clock time for package initialization work 126 # bytes memory allocated on the heap 127 # allocs number of heap allocations 128 129 madvdontneed: setting madvdontneed=0 will use MADV_FREE 130 instead of MADV_DONTNEED on Linux when returning memory to the 131 kernel. This is more efficient, but means RSS numbers will 132 drop only when the OS is under memory pressure. On the BSDs and 133 Illumos/Solaris, setting madvdontneed=1 will use MADV_DONTNEED instead 134 of MADV_FREE. This is less efficient, but causes RSS numbers to drop 135 more quickly. 136 137 memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate. 138 When set to 0 memory profiling is disabled. Refer to the description of 139 MemProfileRate for the default value. 140 141 pagetrace: setting pagetrace=/path/to/file will write out a trace of page events 142 that can be viewed, analyzed, and visualized using the x/debug/cmd/pagetrace tool. 143 Build your program with GOEXPERIMENT=pagetrace to enable this functionality. Do not 144 enable this functionality if your program is a setuid binary as it introduces a security 145 risk in that scenario. Currently not supported on Windows, plan9 or js/wasm. Setting this 146 option for some applications can produce large traces, so use with care. 147 148 invalidptr: invalidptr=1 (the default) causes the garbage collector and stack 149 copier to crash the program if an invalid pointer value (for example, 1) 150 is found in a pointer-typed location. Setting invalidptr=0 disables this check. 151 This should only be used as a temporary workaround to diagnose buggy code. 152 The real fix is to not store integers in pointer-typed locations. 153 154 sbrk: setting sbrk=1 replaces the memory allocator and garbage collector 155 with a trivial allocator that obtains memory from the operating system and 156 never reclaims any memory. 157 158 scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard 159 error, roughly once per GC cycle, summarizing the amount of work done by the 160 scavenger as well as the total amount of memory returned to the operating system 161 and an estimate of physical memory utilization. The format of this line is subject 162 to change, but currently it is: 163 scav # KiB work (bg), # KiB work (eager), # KiB total, #% util 164 where the fields are as follows: 165 # KiB work (bg) the amount of memory returned to the OS in the background since 166 the last line 167 # KiB work (eager) the amount of memory returned to the OS eagerly since the last line 168 # KiB now the amount of address space currently returned to the OS 169 #% util the fraction of all unscavenged heap memory which is in-use 170 If the line ends with "(forced)", then scavenging was forced by a 171 debug.FreeOSMemory() call. 172 173 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit 174 detailed multiline info every X milliseconds, describing state of the scheduler, 175 processors, threads and goroutines. 176 177 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard 178 error every X milliseconds, summarizing the scheduler state. 179 180 tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at 181 which goroutines were created, where N limits the number of ancestor goroutines to 182 report. This also extends the information returned by runtime.Stack. Ancestor's goroutine 183 IDs will refer to the ID of the goroutine at the time of creation; it's possible for this 184 ID to be reused for another goroutine. Setting N to 0 will report no ancestry information. 185 186 tracefpunwindoff: setting tracefpunwindoff=1 forces the execution tracer to 187 use the runtime's default stack unwinder instead of frame pointer unwinding. 188 This increases tracer overhead, but could be helpful as a workaround or for 189 debugging unexpected regressions caused by frame pointer unwinding. 190 191 asyncpreemptoff: asyncpreemptoff=1 disables signal-based 192 asynchronous goroutine preemption. This makes some loops 193 non-preemptible for long periods, which may delay GC and 194 goroutine scheduling. This is useful for debugging GC issues 195 because it also disables the conservative stack scanning used 196 for asynchronously preempted goroutines. 197 198 The net and net/http packages also refer to debugging variables in GODEBUG. 199 See the documentation for those packages for details. 200 201 The GOMAXPROCS variable limits the number of operating system threads that 202 can execute user-level Go code simultaneously. There is no limit to the number of threads 203 that can be blocked in system calls on behalf of Go code; those do not count against 204 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes 205 the limit. 206 207 The GORACE variable configures the race detector, for programs built using -race. 208 See https://golang.org/doc/articles/race_detector.html for details. 209 210 The GOTRACEBACK variable controls the amount of output generated when a Go 211 program fails due to an unrecovered panic or an unexpected runtime condition. 212 By default, a failure prints a stack trace for the current goroutine, 213 eliding functions internal to the run-time system, and then exits with exit code 2. 214 The failure prints stack traces for all goroutines if there is no current goroutine 215 or the failure is internal to the run-time. 216 GOTRACEBACK=none omits the goroutine stack traces entirely. 217 GOTRACEBACK=single (the default) behaves as described above. 218 GOTRACEBACK=all adds stack traces for all user-created goroutines. 219 GOTRACEBACK=system is like “all” but adds stack frames for run-time functions 220 and shows goroutines created internally by the run-time. 221 GOTRACEBACK=crash is like “system” but crashes in an operating system-specific 222 manner instead of exiting. For example, on Unix systems, the crash raises 223 SIGABRT to trigger a core dump. 224 GOTRACEBACK=wer is like “crash” but doesn't disable Windows Error Reporting (WER). 225 For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for 226 none, all, and system, respectively. 227 The runtime/debug package's SetTraceback function allows increasing the 228 amount of output at run time, but it cannot reduce the amount below that 229 specified by the environment variable. 230 See https://golang.org/pkg/runtime/debug/#SetTraceback. 231 232 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete 233 the set of Go environment variables. They influence the building of Go programs 234 (see https://golang.org/cmd/go and https://golang.org/pkg/go/build). 235 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by 236 constants or functions in this package, but they do not influence the execution 237 of the run-time system. 238 239 # Security 240 241 On Unix platforms, Go's runtime system behaves slightly differently when a 242 binary is setuid/setgid or executed with setuid/setgid-like properties, in order 243 to prevent dangerous behaviors. On Linux this is determined by checking for the 244 AT_SECURE flag in the auxiliary vector, on the BSDs and Solaris/Illumos it is 245 determined by checking the issetugid syscall, and on AIX it is determined by 246 checking if the uid/gid match the effective uid/gid. 247 248 When the runtime determines the binary is setuid/setgid-like, it does three main 249 things: 250 - The standard input/output file descriptors (0, 1, 2) are checked to be open. 251 If any of them are closed, they are opened pointing at /dev/null. 252 - The value of the GOTRACEBACK environment variable is set to 'none'. 253 - When a signal is received that terminates the program, or the program 254 encounters an unrecoverable panic that would otherwise override the value 255 of GOTRACEBACK, the goroutine stack, registers, and other memory related 256 information are omitted. 257 */ 258 package runtime 259 260 import ( 261 "internal/goarch" 262 "internal/goos" 263 ) 264 265 // Caller reports file and line number information about function invocations on 266 // the calling goroutine's stack. The argument skip is the number of stack frames 267 // to ascend, with 0 identifying the caller of Caller. (For historical reasons the 268 // meaning of skip differs between Caller and Callers.) The return values report the 269 // program counter, file name, and line number within the file of the corresponding 270 // call. The boolean ok is false if it was not possible to recover the information. 271 func Caller(skip int) (pc uintptr, file string, line int, ok bool) { 272 rpc := make([]uintptr, 1) 273 n := callers(skip+1, rpc[:]) 274 if n < 1 { 275 return 276 } 277 frame, _ := CallersFrames(rpc).Next() 278 return frame.PC, frame.File, frame.Line, frame.PC != 0 279 } 280 281 // Callers fills the slice pc with the return program counters of function invocations 282 // on the calling goroutine's stack. The argument skip is the number of stack frames 283 // to skip before recording in pc, with 0 identifying the frame for Callers itself and 284 // 1 identifying the caller of Callers. 285 // It returns the number of entries written to pc. 286 // 287 // To translate these PCs into symbolic information such as function 288 // names and line numbers, use CallersFrames. CallersFrames accounts 289 // for inlined functions and adjusts the return program counters into 290 // call program counters. Iterating over the returned slice of PCs 291 // directly is discouraged, as is using FuncForPC on any of the 292 // returned PCs, since these cannot account for inlining or return 293 // program counter adjustment. 294 func Callers(skip int, pc []uintptr) int { 295 // runtime.callers uses pc.array==nil as a signal 296 // to print a stack trace. Pick off 0-length pc here 297 // so that we don't let a nil pc slice get to it. 298 if len(pc) == 0 { 299 return 0 300 } 301 return callers(skip, pc) 302 } 303 304 var defaultGOROOT string // set by cmd/link 305 306 // GOROOT returns the root of the Go tree. It uses the 307 // GOROOT environment variable, if set at process start, 308 // or else the root used during the Go build. 309 func GOROOT() string { 310 s := gogetenv("GOROOT") 311 if s != "" { 312 return s 313 } 314 return defaultGOROOT 315 } 316 317 // buildVersion is the Go tree's version string at build time. 318 // 319 // If any GOEXPERIMENTs are set to non-default values, it will include 320 // "X:<GOEXPERIMENT>". 321 // 322 // This is set by the linker. 323 // 324 // This is accessed by "go version <binary>". 325 var buildVersion string 326 327 // Version returns the Go tree's version string. 328 // It is either the commit hash and date at the time of the build or, 329 // when possible, a release tag like "go1.3". 330 func Version() string { 331 return buildVersion 332 } 333 334 // GOOS is the running program's operating system target: 335 // one of darwin, freebsd, linux, and so on. 336 // To view possible combinations of GOOS and GOARCH, run "go tool dist list". 337 const GOOS string = goos.GOOS 338 339 // GOARCH is the running program's architecture target: 340 // one of 386, amd64, arm, s390x, and so on. 341 const GOARCH string = goarch.GOARCH 342