From 300d9d2714164e455abc7990d52de9de6b084df1 Mon Sep 17 00:00:00 2001 From: Steve Muir Date: Thu, 18 Sep 2025 07:54:57 -0700 Subject: [PATCH] runtime: initialise debug settings much earlier in startup process This is necessary specifically to set the value of `debug.decoratemappings` sufficiently early in the startup sequence that all memory ranges allocated can be named appropriately using the new Linux-specific naming API introduced in #71546. Example output (on ARM64): https://gist.github.com/9muir/3667654b9c3f52e8be92756219371672 Fixes: #75324 Change-Id: Ic0b16233f54a45adef1660c4d0df59af2f5af86a Reviewed-on: https://go-review.googlesource.com/c/go/+/703476 Auto-Submit: Michael Knyszek LUCI-TryBot-Result: Go LUCI Reviewed-by: Michael Knyszek --- src/runtime/decoratemappings_test.go | 72 ++++++++++++++++++++++++++++ src/runtime/export_test.go | 4 ++ src/runtime/proc.go | 24 ++++++++-- src/runtime/runtime1.go | 15 +++--- src/runtime/set_vma_name_linux.go | 6 ++- src/runtime/set_vma_name_stub.go | 2 + 6 files changed, 109 insertions(+), 14 deletions(-) create mode 100644 src/runtime/decoratemappings_test.go diff --git a/src/runtime/decoratemappings_test.go b/src/runtime/decoratemappings_test.go new file mode 100644 index 0000000000..7d1121c125 --- /dev/null +++ b/src/runtime/decoratemappings_test.go @@ -0,0 +1,72 @@ +// Copyright 2025 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_test + +import ( + "os" + "regexp" + "runtime" + "testing" +) + +func validateMapLabels(t *testing.T, labels []string) { + // These are the specific region labels that need get added during the + // runtime phase. Hence they are the ones that need to be confirmed as + // present at the time the test reads its own region labels, which + // is sufficient to validate that the default `decoratemappings` value + // (enabled) was set early enough in the init process. + regions := map[string]bool{ + "allspans array": false, + "gc bits": false, + "heap": false, + "heap index": false, + "heap reservation": false, + "immortal metadata": false, + "page alloc": false, + "page alloc index": false, + "page summary": false, + "scavenge index": false, + } + for _, label := range labels { + if _, ok := regions[label]; !ok { + t.Logf("unexpected region label found: \"%s\"", label) + } + regions[label] = true + } + for label, found := range regions { + if !found { + t.Logf("region label missing: \"%s\"", label) + } + } +} + +func TestDecorateMappings(t *testing.T) { + if runtime.GOOS != "linux" { + t.Skip("decoratemappings is only supported on Linux") + // /proc/self/maps is also Linux-specific + } + + var labels []string + if rawMaps, err := os.ReadFile("/proc/self/maps"); err != nil { + t.Fatalf("failed to read /proc/self/maps: %v", err) + } else { + t.Logf("maps:%s\n", string(rawMaps)) + matches := regexp.MustCompile("[^[]+ \\[anon: Go: (.+)\\]\n").FindAllSubmatch(rawMaps, -1) + for _, match_pair := range matches { + // match_pair consists of the matching substring and the parenthesized group + labels = append(labels, string(match_pair[1])) + } + } + t.Logf("DebugDecorateMappings: %v", *runtime.DebugDecorateMappings) + if *runtime.DebugDecorateMappings != 0 && runtime.SetVMANameSupported() { + validateMapLabels(t, labels) + } else { + if len(labels) > 0 { + t.Errorf("unexpected mapping labels present: %v", labels) + } else { + t.Skip("mapping labels absent as expected") + } + } +} diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go index 2a70111568..9f2fcacc30 100644 --- a/src/runtime/export_test.go +++ b/src/runtime/export_test.go @@ -1936,3 +1936,7 @@ func (t *TraceStackTable) Reset() { func TraceStack(gp *G, tab *TraceStackTable) { traceStack(0, gp, (*traceStackTable)(tab)) } + +var DebugDecorateMappings = &debug.decoratemappings + +func SetVMANameSupported() bool { return setVMANameSupported() } diff --git a/src/runtime/proc.go b/src/runtime/proc.go index 2c42cad6c1..4b1ab1af6a 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -789,7 +789,9 @@ func cpuinit(env string) { // getGodebugEarly extracts the environment variable GODEBUG from the environment on // Unix-like operating systems and returns it. This function exists to extract GODEBUG // early before much of the runtime is initialized. -func getGodebugEarly() string { +// +// Returns nil, false if OS doesn't provide env vars early in the init sequence. +func getGodebugEarly() (string, bool) { const prefix = "GODEBUG=" var env string switch GOOS { @@ -807,12 +809,16 @@ func getGodebugEarly() string { s := unsafe.String(p, findnull(p)) if stringslite.HasPrefix(s, prefix) { - env = gostring(p)[len(prefix):] + env = gostringnocopy(p)[len(prefix):] break } } + break + + default: + return "", false } - return env + return env, true } // The bootstrap sequence is: @@ -859,12 +865,15 @@ func schedinit() { // The world starts stopped. worldStopped() + godebug, parsedGodebug := getGodebugEarly() + if parsedGodebug { + parseRuntimeDebugVars(godebug) + } ticks.init() // run as early as possible moduledataverify() stackinit() randinit() // must run before mallocinit, alginit, mcommoninit mallocinit() - godebug := getGodebugEarly() cpuinit(godebug) // must run before alginit alginit() // maps, hash, rand must not be used before this call mcommoninit(gp.m, -1) @@ -880,7 +889,12 @@ func schedinit() { goenvs() secure() checkfds() - parsedebugvars() + if !parsedGodebug { + // Some platforms, e.g., Windows, didn't make env vars available "early", + // so try again now. + parseRuntimeDebugVars(gogetenv("GODEBUG")) + } + finishDebugVarsSetup() gcinit() // Allocate stack space that can be used when crashing due to bad stack diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go index 424745d235..15b546783b 100644 --- a/src/runtime/runtime1.go +++ b/src/runtime/runtime1.go @@ -402,7 +402,7 @@ var dbgvars = []*dbgVar{ {name: "updatemaxprocs", value: &debug.updatemaxprocs, def: 1}, } -func parsedebugvars() { +func parseRuntimeDebugVars(godebug string) { // defaults debug.cgocheck = 1 debug.invalidptr = 1 @@ -420,12 +420,6 @@ func parsedebugvars() { } debug.traceadvanceperiod = defaultTraceAdvancePeriod - godebug := gogetenv("GODEBUG") - - p := new(string) - *p = godebug - godebugEnv.Store(p) - // apply runtime defaults, if any for _, v := range dbgvars { if v.def != 0 { @@ -437,7 +431,6 @@ func parsedebugvars() { } } } - // apply compile-time GODEBUG settings parsegodebug(godebugDefault, nil) @@ -463,6 +456,12 @@ func parsedebugvars() { if debug.gccheckmark > 0 { debug.asyncpreemptoff = 1 } +} + +func finishDebugVarsSetup() { + p := new(string) + *p = gogetenv("GODEBUG") + godebugEnv.Store(p) setTraceback(gogetenv("GOTRACEBACK")) traceback_env = traceback_cache diff --git a/src/runtime/set_vma_name_linux.go b/src/runtime/set_vma_name_linux.go index 9b6654f332..03c7739c34 100644 --- a/src/runtime/set_vma_name_linux.go +++ b/src/runtime/set_vma_name_linux.go @@ -14,9 +14,13 @@ import ( var prSetVMAUnsupported atomic.Bool +func setVMANameSupported() bool { + return !prSetVMAUnsupported.Load() +} + // setVMAName calls prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, name) func setVMAName(start unsafe.Pointer, length uintptr, name string) { - if debug.decoratemappings == 0 || prSetVMAUnsupported.Load() { + if debug.decoratemappings == 0 || !setVMANameSupported() { return } diff --git a/src/runtime/set_vma_name_stub.go b/src/runtime/set_vma_name_stub.go index 38f65fd592..6cb01ebf50 100644 --- a/src/runtime/set_vma_name_stub.go +++ b/src/runtime/set_vma_name_stub.go @@ -10,3 +10,5 @@ import "unsafe" // setVMAName isn’t implemented func setVMAName(start unsafe.Pointer, len uintptr, name string) {} + +func setVMANameSupported() bool { return false }