runtime: introduce GODEBUG env var

Currently it replaces GOGCTRACE env var (GODEBUG=gctrace=1).
The plan is to extend it with other type of debug tracing,
e.g. GODEBUG=gctrace=1,schedtrace=100.

R=rsc
CC=bradfitz, daniel.morsing, gobot, golang-dev
https://golang.org/cl/10026045

src/pkg/runtime/crash_test.go

@@ -14,7 +14,7 @@ import (
 	"text/template"
 )
 
-// testEnv excludes GOGCTRACE from the environment
+// testEnv excludes GODEBUG from the environment
 // to prevent its output from breaking tests that
 // are trying to parse other command output.
 func testEnv(cmd *exec.Cmd) *exec.Cmd {
@@ -22,7 +22,7 @@ func testEnv(cmd *exec.Cmd) *exec.Cmd {
 		panic("environment already set")
 	}
 	for _, env := range os.Environ() {
-		if strings.HasPrefix(env, "GOGCTRACE=") {
+		if strings.HasPrefix(env, "GODEBUG=") {
 			continue
 		}
 		cmd.Env = append(cmd.Env, env)

src/pkg/runtime/extern.go

@@ -21,10 +21,11 @@ is GOGC=100. Setting GOGC=off disables the garbage collector entirely.
 The runtime/debug package's SetGCPercent function allows changing this
 percentage at run time. See http://golang.org/pkg/runtime/debug/#SetGCPercent.
 
-The GOGCTRACE variable controls debug output from the garbage collector.
-Setting GOGCTRACE=1 causes the garbage collector to emit a single line to standard
+The GODEBUG variable controls debug output from the runtime. GODEBUG value is
+a comma-separated list of name=val pairs. Supported names are:
+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. Setting GOGCTRACE=2 emits the same summary but also
+length of the pause. Setting gctrace=2 emits the same summary but also
 repeats each collection.
 
 The GOMAXPROCS variable limits the number of operating system threads that

src/pkg/runtime/mgc0.c

@@ -82,8 +82,6 @@ enum {
 //
 uint32 runtime·worldsema = 1;
 
-static int32 gctrace;
-
 typedef struct Obj Obj;
 struct Obj
 {
@@ -1950,7 +1948,6 @@ static FuncVal runfinqv = {runfinq};
 void
 runtime·gc(int32 force)
 {
-	byte *p;
 	struct gc_args a;
 	int32 i;
 
@@ -1978,10 +1975,6 @@ runtime·gc(int32 force)
 		if(gcpercent == GcpercentUnknown)
 			gcpercent = readgogc();
 		runtime·unlock(&runtime·mheap);
-
-		p = runtime·getenv("GOGCTRACE");
-		if(p != nil)
-			gctrace = runtime·atoi(p);
 	}
 	if(gcpercent < 0)
 		return;
@@ -2004,7 +1997,7 @@ runtime·gc(int32 force)
 	// the root set down a bit (g0 stacks are not scanned, and
 	// we don't need to scan gc's internal state).  Also an
 	// enabler for copyable stacks.
-	for(i = 0; i < (gctrace > 1 ? 2 : 1); i++) {
+	for(i = 0; i < (runtime·debug.gctrace > 1 ? 2 : 1); i++) {
 		if(g == m->g0) {
 			// already on g0
 			gc(&a);
@@ -2068,7 +2061,7 @@ gc(struct gc_args *args)
 
 	heap0 = 0;
 	obj0 = 0;
-	if(gctrace) {
+	if(runtime·debug.gctrace) {
 		updatememstats(nil);
 		heap0 = mstats.heap_alloc;
 		obj0 = mstats.nmalloc - mstats.nfree;
@@ -2131,7 +2124,7 @@ gc(struct gc_args *args)
 	if(mstats.debuggc)
 		runtime·printf("pause %D\n", t4-t0);
 
-	if(gctrace) {
+	if(runtime·debug.gctrace) {
 		updatememstats(&stats);
 		heap1 = mstats.heap_alloc;
 		obj1 = mstats.nmalloc - mstats.nfree;

src/pkg/runtime/mheap.c

@@ -441,8 +441,6 @@ runtime·MHeap_Scavenger(void)
 	uint64 tick, now, forcegc, limit;
 	uint32 k;
 	uintptr sumreleased;
-	byte *env;
-	bool trace;
 	Note note, *notep;
 
 	g->issystem = true;
@@ -459,11 +457,6 @@ runtime·MHeap_Scavenger(void)
 	else
 		tick = limit/2;
 
-	trace = false;
-	env = runtime·getenv("GOGCTRACE");
-	if(env != nil)
-		trace = runtime·atoi(env) > 0;
-
 	h = &runtime·mheap;
 	for(k=0;; k++) {
 		runtime·noteclear(&note);
@@ -484,7 +477,7 @@ runtime·MHeap_Scavenger(void)
 			runtime·entersyscallblock();
 			runtime·notesleep(&note);
 			runtime·exitsyscall();
-			if(trace)
+			if(runtime·debug.gctrace > 0)
 				runtime·printf("scvg%d: GC forced\n", k);
 			runtime·lock(h);
 			now = runtime·nanotime();
@@ -492,7 +485,7 @@ runtime·MHeap_Scavenger(void)
 		sumreleased = scavenge(now, limit);
 		runtime·unlock(h);
 
-		if(trace) {
+		if(runtime·debug.gctrace > 0) {
 			if(sumreleased > 0)
 				runtime·printf("scvg%d: %p MB released\n", k, sumreleased>>20);
 			runtime·printf("scvg%d: inuse: %D, idle: %D, sys: %D, released: %D, consumed: %D (MB)\n",

src/pkg/runtime/proc.c

@@ -132,6 +132,7 @@ runtime·schedinit(void)
 
 	runtime·goargs();
 	runtime·goenvs();
+	runtime·parsedebugvars();
 
 	// Allocate internal symbol table representation now, we need it for GC anyway.
 	runtime·symtabinit();

src/pkg/runtime/race/race_test.go

@@ -147,7 +147,7 @@ func runTests() ([]byte, error) {
 	// It is required because the tests contain a lot of data races on the same addresses
 	// (the tests are simple and the memory is constantly reused).
 	for _, env := range os.Environ() {
-		if strings.HasPrefix(env, "GOMAXPROCS=") || strings.HasPrefix(env, "GOGCTRACE=") {
+		if strings.HasPrefix(env, "GOMAXPROCS=") || strings.HasPrefix(env, "GODEBUG=") {
 			continue
 		}
 		cmd.Env = append(cmd.Env, env)

src/pkg/runtime/runtime.c

@@ -365,3 +365,34 @@ runtime∕pprof·runtime_cyclesPerSecond(int64 res)
 	res = runtime·tickspersecond();
 	FLUSH(&res);
 }
+
+DebugVars	runtime·debug;
+
+static struct {
+	int8*	name;
+	int32*	value;
+} dbgvar[] = {
+	{"gctrace", &runtime·debug.gctrace},
+};
+
+void
+runtime·parsedebugvars(void)
+{
+	byte *p;
+	int32 i, n;
+
+	p = runtime·getenv("GODEBUG");
+	if(p == nil)
+		return;
+	for(;;) {
+		for(i=0; i<nelem(dbgvar); i++) {
+			n = runtime·findnull((byte*)dbgvar[i].name);
+			if(runtime·mcmp(p, (byte*)dbgvar[i].name, n) == 0 && p[n] == '=')
+				*dbgvar[i].value = runtime·atoi(p+n+1);
+		}
+		p = runtime·strstr(p, (byte*)",");
+		if(p == nil)
+			break;
+		p++;
+	}
+}

src/pkg/runtime/runtime.h

@@ -86,6 +86,7 @@ typedef	struct	ParFor		ParFor;
 typedef	struct	ParForThread	ParForThread;
 typedef	struct	CgoMal		CgoMal;
 typedef	struct	PollDesc	PollDesc;
+typedef	struct	DebugVars	DebugVars;
 
 /*
  * Per-CPU declaration.
@@ -525,6 +526,12 @@ struct CgoMal
 	void	*alloc;
 };
 
+// Holds variables parsed from GODEBUG env var.
+struct DebugVars
+{
+	int32	gctrace;
+};
+
 /*
  * defined macros
  *    you need super-gopher-guru privilege
@@ -702,6 +709,7 @@ extern	uint32	runtime·maxstring;
 extern	uint32	runtime·Hchansize;
 extern	uint32	runtime·cpuid_ecx;
 extern	uint32	runtime·cpuid_edx;
+extern	DebugVars	runtime·debug;
 
 /*
  * common functions and data
@@ -841,6 +849,7 @@ int32	runtime·netpollopen(uintptr, PollDesc*);
 int32   runtime·netpollclose(uintptr);
 void	runtime·netpollready(G**, PollDesc*, int32);
 void	runtime·crash(void);
+void	runtime·parsedebugvars(void);
 void	_rt0_go(void);
 
 #pragma	varargck	argpos	runtime·printf	1