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mgc0.c
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mgc0.c
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// 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.
// Garbage collector (GC).
//
// GC is:
// - mark&sweep
// - mostly precise (with the exception of some C-allocated objects, assembly frames/arguments, etc)
// - parallel (up to MaxGcproc threads)
// - partially concurrent (mark is stop-the-world, while sweep is concurrent)
// - non-moving/non-compacting
// - full (non-partial)
//
// GC rate.
// Next GC is after we've allocated an extra amount of memory proportional to
// the amount already in use. The proportion is controlled by GOGC environment variable
// (100 by default). If GOGC=100 and we're using 4M, we'll GC again when we get to 8M
// (this mark is tracked in next_gc variable). This keeps the GC cost in linear
// proportion to the allocation cost. Adjusting GOGC just changes the linear constant
// (and also the amount of extra memory used).
//
// Concurrent sweep.
// The sweep phase proceeds concurrently with normal program execution.
// The heap is swept span-by-span both lazily (when a goroutine needs another span)
// and concurrently in a background goroutine (this helps programs that are not CPU bound).
// However, at the end of the stop-the-world GC phase we don't know the size of the live heap,
// and so next_gc calculation is tricky and happens as follows.
// At the end of the stop-the-world phase next_gc is conservatively set based on total
// heap size; all spans are marked as "needs sweeping".
// Whenever a span is swept, next_gc is decremented by GOGC*newly_freed_memory.
// The background sweeper goroutine simply sweeps spans one-by-one bringing next_gc
// closer to the target value. However, this is not enough to avoid over-allocating memory.
// Consider that a goroutine wants to allocate a new span for a large object and
// there are no free swept spans, but there are small-object unswept spans.
// If the goroutine naively allocates a new span, it can surpass the yet-unknown
// target next_gc value. In order to prevent such cases (1) when a goroutine needs
// to allocate a new small-object span, it sweeps small-object spans for the same
// object size until it frees at least one object; (2) when a goroutine needs to
// allocate large-object span from heap, it sweeps spans until it frees at least
// that many pages into heap. Together these two measures ensure that we don't surpass
// target next_gc value by a large margin. There is an exception: if a goroutine sweeps
// and frees two nonadjacent one-page spans to the heap, it will allocate a new two-page span,
// but there can still be other one-page unswept spans which could be combined into a two-page span.
// It's critical to ensure that no operations proceed on unswept spans (that would corrupt
// mark bits in GC bitmap). During GC all mcaches are flushed into the central cache,
// so they are empty. When a goroutine grabs a new span into mcache, it sweeps it.
// When a goroutine explicitly frees an object or sets a finalizer, it ensures that
// the span is swept (either by sweeping it, or by waiting for the concurrent sweep to finish).
// The finalizer goroutine is kicked off only when all spans are swept.
// When the next GC starts, it sweeps all not-yet-swept spans (if any).
#include "runtime.h"
#include "arch_GOARCH.h"
#include "malloc.h"
#include "stack.h"
#include "mgc0.h"
#include "chan.h"
#include "race.h"
#include "type.h"
#include "typekind.h"
#include "funcdata.h"
#include "../../cmd/ld/textflag.h"
enum {
Debug = 0,
CollectStats = 0,
ConcurrentSweep = 1,
WorkbufSize = 16*1024,
FinBlockSize = 4*1024,
handoffThreshold = 4,
IntermediateBufferCapacity = 64,
// Bits in type information
PRECISE = 1,
LOOP = 2,
PC_BITS = PRECISE | LOOP,
RootData = 0,
RootBss = 1,
RootFinalizers = 2,
RootSpanTypes = 3,
RootFlushCaches = 4,
RootCount = 5,
};
#define GcpercentUnknown (-2)
// Initialized from $GOGC. GOGC=off means no gc.
static int32 gcpercent = GcpercentUnknown;
static FuncVal* poolcleanup;
void
sync·runtime_registerPoolCleanup(FuncVal *f)
{
poolcleanup = f;
}
static void
clearpools(void)
{
P *p, **pp;
MCache *c;
int32 i;
// clear sync.Pool's
if(poolcleanup != nil)
reflect·call(poolcleanup, nil, 0, 0);
for(pp=runtime·allp; p=*pp; pp++) {
// clear tinyalloc pool
c = p->mcache;
if(c != nil) {
c->tiny = nil;
c->tinysize = 0;
}
// clear defer pools
for(i=0; i<nelem(p->deferpool); i++)
p->deferpool[i] = nil;
}
}
// Holding worldsema grants an M the right to try to stop the world.
// The procedure is:
//
// runtime·semacquire(&runtime·worldsema);
// m->gcing = 1;
// runtime·stoptheworld();
//
// ... do stuff ...
//
// m->gcing = 0;
// runtime·semrelease(&runtime·worldsema);
// runtime·starttheworld();
//
uint32 runtime·worldsema = 1;
typedef struct Obj Obj;
struct Obj
{
byte *p; // data pointer
uintptr n; // size of data in bytes
uintptr ti; // type info
};
typedef struct Workbuf Workbuf;
struct Workbuf
{
#define SIZE (WorkbufSize-sizeof(LFNode)-sizeof(uintptr))
LFNode node; // must be first
uintptr nobj;
Obj obj[SIZE/sizeof(Obj) - 1];
uint8 _padding[SIZE%sizeof(Obj) + sizeof(Obj)];
#undef SIZE
};
typedef struct Finalizer Finalizer;
struct Finalizer
{
FuncVal *fn;
void *arg;
uintptr nret;
Type *fint;
PtrType *ot;
};
typedef struct FinBlock FinBlock;
struct FinBlock
{
FinBlock *alllink;
FinBlock *next;
int32 cnt;
int32 cap;
Finalizer fin[1];
};
extern byte data[];
extern byte edata[];
extern byte bss[];
extern byte ebss[];
extern byte gcdata[];
extern byte gcbss[];
static Lock finlock; // protects the following variables
static FinBlock *finq; // list of finalizers that are to be executed
static FinBlock *finc; // cache of free blocks
static FinBlock *allfin; // list of all blocks
bool runtime·fingwait;
bool runtime·fingwake;
static Lock gclock;
static G* fing;
static void runfinq(void);
static void bgsweep(void);
static Workbuf* getempty(Workbuf*);
static Workbuf* getfull(Workbuf*);
static void putempty(Workbuf*);
static Workbuf* handoff(Workbuf*);
static void gchelperstart(void);
static void flushallmcaches(void);
static bool scanframe(Stkframe *frame, void *wbufp);
static void addstackroots(G *gp, Workbuf **wbufp);
static FuncVal runfinqv = {runfinq};
static FuncVal bgsweepv = {bgsweep};
static struct {
uint64 full; // lock-free list of full blocks
uint64 empty; // lock-free list of empty blocks
byte pad0[CacheLineSize]; // prevents false-sharing between full/empty and nproc/nwait
uint32 nproc;
int64 tstart;
volatile uint32 nwait;
volatile uint32 ndone;
Note alldone;
ParFor *markfor;
Lock;
byte *chunk;
uintptr nchunk;
} work;
enum {
GC_DEFAULT_PTR = GC_NUM_INSTR,
GC_CHAN,
GC_NUM_INSTR2
};
static struct {
struct {
uint64 sum;
uint64 cnt;
} ptr;
uint64 nbytes;
struct {
uint64 sum;
uint64 cnt;
uint64 notype;
uint64 typelookup;
} obj;
uint64 rescan;
uint64 rescanbytes;
uint64 instr[GC_NUM_INSTR2];
uint64 putempty;
uint64 getfull;
struct {
uint64 foundbit;
uint64 foundword;
uint64 foundspan;
} flushptrbuf;
struct {
uint64 foundbit;
uint64 foundword;
uint64 foundspan;
} markonly;
uint32 nbgsweep;
uint32 npausesweep;
} gcstats;
// markonly marks an object. It returns true if the object
// has been marked by this function, false otherwise.
// This function doesn't append the object to any buffer.
static bool
markonly(void *obj)
{
byte *p;
uintptr *bitp, bits, shift, x, xbits, off, j;
MSpan *s;
PageID k;
// Words outside the arena cannot be pointers.
if(obj < runtime·mheap.arena_start || obj >= runtime·mheap.arena_used)
return false;
// obj may be a pointer to a live object.
// Try to find the beginning of the object.
// Round down to word boundary.
obj = (void*)((uintptr)obj & ~((uintptr)PtrSize-1));
// Find bits for this word.
off = (uintptr*)obj - (uintptr*)runtime·mheap.arena_start;
bitp = (uintptr*)runtime·mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
// Pointing at the beginning of a block?
if((bits & (bitAllocated|bitBlockBoundary)) != 0) {
if(CollectStats)
runtime·xadd64(&gcstats.markonly.foundbit, 1);
goto found;
}
// Pointing just past the beginning?
// Scan backward a little to find a block boundary.
for(j=shift; j-->0; ) {
if(((xbits>>j) & (bitAllocated|bitBlockBoundary)) != 0) {
shift = j;
bits = xbits>>shift;
if(CollectStats)
runtime·xadd64(&gcstats.markonly.foundword, 1);
goto found;
}
}
// Otherwise consult span table to find beginning.
// (Manually inlined copy of MHeap_LookupMaybe.)
k = (uintptr)obj>>PageShift;
x = k;
x -= (uintptr)runtime·mheap.arena_start>>PageShift;
s = runtime·mheap.spans[x];
if(s == nil || k < s->start || obj >= s->limit || s->state != MSpanInUse)
return false;
p = (byte*)((uintptr)s->start<<PageShift);
if(s->sizeclass == 0) {
obj = p;
} else {
uintptr size = s->elemsize;
int32 i = ((byte*)obj - p)/size;
obj = p+i*size;
}
// Now that we know the object header, reload bits.
off = (uintptr*)obj - (uintptr*)runtime·mheap.arena_start;
bitp = (uintptr*)runtime·mheap.arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
if(CollectStats)
runtime·xadd64(&gcstats.markonly.foundspan, 1);
found:
// Now we have bits, bitp, and shift correct for
// obj pointing at the base of the object.
// Only care about allocated and not marked.
if((bits & (bitAllocated|bitMarked)) != bitAllocated)
return false;
if(work.nproc == 1)
*bitp |= bitMarked<<shift;
else {
for(;;) {
x = *bitp;
if(x & (bitMarked<<shift))
return false;
if(runtime·casp((void**)bitp, (void*)x, (void*)(x|(bitMarked<<shift))))
break;
}
}
// The object is now marked
return true;
}
// PtrTarget is a structure used by intermediate buffers.
// The intermediate buffers hold GC data before it
// is moved/flushed to the work buffer (Workbuf).
// The size of an intermediate buffer is very small,
// such as 32 or 64 elements.
typedef struct PtrTarget PtrTarget;
struct PtrTarget
{
void *p;
uintptr ti;
};
typedef struct Scanbuf Scanbuf;
struct Scanbuf
{
struct {
PtrTarget *begin;
PtrTarget *end;
PtrTarget *pos;
} ptr;
struct {
Obj *begin;
Obj *end;
Obj *pos;
} obj;
Workbuf *wbuf;
Obj *wp;
uintptr nobj;
};
typedef struct BufferList BufferList;
struct BufferList
{
PtrTarget ptrtarget[IntermediateBufferCapacity];
Obj obj[IntermediateBufferCapacity];
uint32 busy;
byte pad[CacheLineSize];
};
#pragma dataflag NOPTR
static BufferList bufferList[MaxGcproc];
static Type *itabtype;
static void enqueue(Obj obj, Workbuf **_wbuf, Obj **_wp, uintptr *_nobj);
// flushptrbuf moves data from the PtrTarget buffer to the work buffer.
// The PtrTarget buffer contains blocks irrespective of whether the blocks have been marked or scanned,
// while the work buffer contains blocks which have been marked
// and are prepared to be scanned by the garbage collector.
//
// _wp, _wbuf, _nobj are input/output parameters and are specifying the work buffer.
//
// A simplified drawing explaining how the todo-list moves from a structure to another:
//
// scanblock
// (find pointers)
// Obj ------> PtrTarget (pointer targets)
// ↑ |
// | |
// `----------'
// flushptrbuf
// (find block start, mark and enqueue)
static void
flushptrbuf(Scanbuf *sbuf)
{
byte *p, *arena_start, *obj;
uintptr size, *bitp, bits, shift, j, x, xbits, off, nobj, ti, n;
MSpan *s;
PageID k;
Obj *wp;
Workbuf *wbuf;
PtrTarget *ptrbuf;
PtrTarget *ptrbuf_end;
arena_start = runtime·mheap.arena_start;
wp = sbuf->wp;
wbuf = sbuf->wbuf;
nobj = sbuf->nobj;
ptrbuf = sbuf->ptr.begin;
ptrbuf_end = sbuf->ptr.pos;
n = ptrbuf_end - sbuf->ptr.begin;
sbuf->ptr.pos = sbuf->ptr.begin;
if(CollectStats) {
runtime·xadd64(&gcstats.ptr.sum, n);
runtime·xadd64(&gcstats.ptr.cnt, 1);
}
// If buffer is nearly full, get a new one.
if(wbuf == nil || nobj+n >= nelem(wbuf->obj)) {
if(wbuf != nil)
wbuf->nobj = nobj;
wbuf = getempty(wbuf);
wp = wbuf->obj;
nobj = 0;
if(n >= nelem(wbuf->obj))
runtime·throw("ptrbuf has to be smaller than WorkBuf");
}
while(ptrbuf < ptrbuf_end) {
obj = ptrbuf->p;
ti = ptrbuf->ti;
ptrbuf++;
// obj belongs to interval [mheap.arena_start, mheap.arena_used).
if(Debug > 1) {
if(obj < runtime·mheap.arena_start || obj >= runtime·mheap.arena_used)
runtime·throw("object is outside of mheap");
}
// obj may be a pointer to a live object.
// Try to find the beginning of the object.
// Round down to word boundary.
if(((uintptr)obj & ((uintptr)PtrSize-1)) != 0) {
obj = (void*)((uintptr)obj & ~((uintptr)PtrSize-1));
ti = 0;
}
// Find bits for this word.
off = (uintptr*)obj - (uintptr*)arena_start;
bitp = (uintptr*)arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
// Pointing at the beginning of a block?
if((bits & (bitAllocated|bitBlockBoundary)) != 0) {
if(CollectStats)
runtime·xadd64(&gcstats.flushptrbuf.foundbit, 1);
goto found;
}
ti = 0;
// Pointing just past the beginning?
// Scan backward a little to find a block boundary.
for(j=shift; j-->0; ) {
if(((xbits>>j) & (bitAllocated|bitBlockBoundary)) != 0) {
obj = (byte*)obj - (shift-j)*PtrSize;
shift = j;
bits = xbits>>shift;
if(CollectStats)
runtime·xadd64(&gcstats.flushptrbuf.foundword, 1);
goto found;
}
}
// Otherwise consult span table to find beginning.
// (Manually inlined copy of MHeap_LookupMaybe.)
k = (uintptr)obj>>PageShift;
x = k;
x -= (uintptr)arena_start>>PageShift;
s = runtime·mheap.spans[x];
if(s == nil || k < s->start || obj >= s->limit || s->state != MSpanInUse)
continue;
p = (byte*)((uintptr)s->start<<PageShift);
if(s->sizeclass == 0) {
obj = p;
} else {
size = s->elemsize;
int32 i = ((byte*)obj - p)/size;
obj = p+i*size;
}
// Now that we know the object header, reload bits.
off = (uintptr*)obj - (uintptr*)arena_start;
bitp = (uintptr*)arena_start - off/wordsPerBitmapWord - 1;
shift = off % wordsPerBitmapWord;
xbits = *bitp;
bits = xbits >> shift;
if(CollectStats)
runtime·xadd64(&gcstats.flushptrbuf.foundspan, 1);
found:
// Now we have bits, bitp, and shift correct for
// obj pointing at the base of the object.
// Only care about allocated and not marked.
if((bits & (bitAllocated|bitMarked)) != bitAllocated)
continue;
if(work.nproc == 1)
*bitp |= bitMarked<<shift;
else {
for(;;) {
x = *bitp;
if(x & (bitMarked<<shift))
goto continue_obj;
if(runtime·casp((void**)bitp, (void*)x, (void*)(x|(bitMarked<<shift))))
break;
}
}
// If object has no pointers, don't need to scan further.
if((bits & bitScan) == 0)
continue;
// Ask span about size class.
// (Manually inlined copy of MHeap_Lookup.)
x = (uintptr)obj >> PageShift;
x -= (uintptr)arena_start>>PageShift;
s = runtime·mheap.spans[x];
PREFETCH(obj);
*wp = (Obj){obj, s->elemsize, ti};
wp++;
nobj++;
continue_obj:;
}
// If another proc wants a pointer, give it some.
if(work.nwait > 0 && nobj > handoffThreshold && work.full == 0) {
wbuf->nobj = nobj;
wbuf = handoff(wbuf);
nobj = wbuf->nobj;
wp = wbuf->obj + nobj;
}
sbuf->wp = wp;
sbuf->wbuf = wbuf;
sbuf->nobj = nobj;
}
static void
flushobjbuf(Scanbuf *sbuf)
{
uintptr nobj, off;
Obj *wp, obj;
Workbuf *wbuf;
Obj *objbuf;
Obj *objbuf_end;
wp = sbuf->wp;
wbuf = sbuf->wbuf;
nobj = sbuf->nobj;
objbuf = sbuf->obj.begin;
objbuf_end = sbuf->obj.pos;
sbuf->obj.pos = sbuf->obj.begin;
while(objbuf < objbuf_end) {
obj = *objbuf++;
// Align obj.b to a word boundary.
off = (uintptr)obj.p & (PtrSize-1);
if(off != 0) {
obj.p += PtrSize - off;
obj.n -= PtrSize - off;
obj.ti = 0;
}
if(obj.p == nil || obj.n == 0)
continue;
// If buffer is full, get a new one.
if(wbuf == nil || nobj >= nelem(wbuf->obj)) {
if(wbuf != nil)
wbuf->nobj = nobj;
wbuf = getempty(wbuf);
wp = wbuf->obj;
nobj = 0;
}
*wp = obj;
wp++;
nobj++;
}
// If another proc wants a pointer, give it some.
if(work.nwait > 0 && nobj > handoffThreshold && work.full == 0) {
wbuf->nobj = nobj;
wbuf = handoff(wbuf);
nobj = wbuf->nobj;
wp = wbuf->obj + nobj;
}
sbuf->wp = wp;
sbuf->wbuf = wbuf;
sbuf->nobj = nobj;
}
// Program that scans the whole block and treats every block element as a potential pointer
static uintptr defaultProg[2] = {PtrSize, GC_DEFAULT_PTR};
// Hchan program
static uintptr chanProg[2] = {0, GC_CHAN};
// Local variables of a program fragment or loop
typedef struct Frame Frame;
struct Frame {
uintptr count, elemsize, b;
uintptr *loop_or_ret;
};
// Sanity check for the derived type info objti.
static void
checkptr(void *obj, uintptr objti)
{
uintptr *pc1, *pc2, type, tisize, i, j, x;
byte *objstart;
Type *t;
MSpan *s;
if(!Debug)
runtime·throw("checkptr is debug only");
if(obj < runtime·mheap.arena_start || obj >= runtime·mheap.arena_used)
return;
type = runtime·gettype(obj);
t = (Type*)(type & ~(uintptr)(PtrSize-1));
if(t == nil)
return;
x = (uintptr)obj >> PageShift;
x -= (uintptr)(runtime·mheap.arena_start)>>PageShift;
s = runtime·mheap.spans[x];
objstart = (byte*)((uintptr)s->start<<PageShift);
if(s->sizeclass != 0) {
i = ((byte*)obj - objstart)/s->elemsize;
objstart += i*s->elemsize;
}
tisize = *(uintptr*)objti;
// Sanity check for object size: it should fit into the memory block.
if((byte*)obj + tisize > objstart + s->elemsize) {
runtime·printf("object of type '%S' at %p/%p does not fit in block %p/%p\n",
*t->string, obj, tisize, objstart, s->elemsize);
runtime·throw("invalid gc type info");
}
if(obj != objstart)
return;
// If obj points to the beginning of the memory block,
// check type info as well.
if(t->string == nil ||
// Gob allocates unsafe pointers for indirection.
(runtime·strcmp(t->string->str, (byte*)"unsafe.Pointer") &&
// Runtime and gc think differently about closures.
runtime·strstr(t->string->str, (byte*)"struct { F uintptr") != t->string->str)) {
pc1 = (uintptr*)objti;
pc2 = (uintptr*)t->gc;
// A simple best-effort check until first GC_END.
for(j = 1; pc1[j] != GC_END && pc2[j] != GC_END; j++) {
if(pc1[j] != pc2[j]) {
runtime·printf("invalid gc type info for '%s', type info %p [%d]=%p, block info %p [%d]=%p\n",
t->string ? (int8*)t->string->str : (int8*)"?", pc1, (int32)j, pc1[j], pc2, (int32)j, pc2[j]);
runtime·throw("invalid gc type info");
}
}
}
}
// scanblock scans a block of n bytes starting at pointer b for references
// to other objects, scanning any it finds recursively until there are no
// unscanned objects left. Instead of using an explicit recursion, it keeps
// a work list in the Workbuf* structures and loops in the main function
// body. Keeping an explicit work list is easier on the stack allocator and
// more efficient.
static void
scanblock(Workbuf *wbuf, bool keepworking)
{
byte *b, *arena_start, *arena_used;
uintptr n, i, end_b, elemsize, size, ti, objti, count, type, nobj;
uintptr *pc, precise_type, nominal_size;
uintptr *chan_ret, chancap;
void *obj;
Type *t, *et;
Slice *sliceptr;
String *stringptr;
Frame *stack_ptr, stack_top, stack[GC_STACK_CAPACITY+4];
BufferList *scanbuffers;
Scanbuf sbuf;
Eface *eface;
Iface *iface;
Hchan *chan;
ChanType *chantype;
Obj *wp;
if(sizeof(Workbuf) % WorkbufSize != 0)
runtime·throw("scanblock: size of Workbuf is suboptimal");
// Memory arena parameters.
arena_start = runtime·mheap.arena_start;
arena_used = runtime·mheap.arena_used;
stack_ptr = stack+nelem(stack)-1;
precise_type = false;
nominal_size = 0;
if(wbuf) {
nobj = wbuf->nobj;
wp = &wbuf->obj[nobj];
} else {
nobj = 0;
wp = nil;
}
// Initialize sbuf
scanbuffers = &bufferList[m->helpgc];
sbuf.ptr.begin = sbuf.ptr.pos = &scanbuffers->ptrtarget[0];
sbuf.ptr.end = sbuf.ptr.begin + nelem(scanbuffers->ptrtarget);
sbuf.obj.begin = sbuf.obj.pos = &scanbuffers->obj[0];
sbuf.obj.end = sbuf.obj.begin + nelem(scanbuffers->obj);
sbuf.wbuf = wbuf;
sbuf.wp = wp;
sbuf.nobj = nobj;
// (Silence the compiler)
chan = nil;
chantype = nil;
chan_ret = nil;
goto next_block;
for(;;) {
// Each iteration scans the block b of length n, queueing pointers in
// the work buffer.
if(CollectStats) {
runtime·xadd64(&gcstats.nbytes, n);
runtime·xadd64(&gcstats.obj.sum, sbuf.nobj);
runtime·xadd64(&gcstats.obj.cnt, 1);
}
if(ti != 0) {
if(Debug > 1) {
runtime·printf("scanblock %p %D ti %p\n", b, (int64)n, ti);
}
pc = (uintptr*)(ti & ~(uintptr)PC_BITS);
precise_type = (ti & PRECISE);
stack_top.elemsize = pc[0];
if(!precise_type)
nominal_size = pc[0];
if(ti & LOOP) {
stack_top.count = 0; // 0 means an infinite number of iterations
stack_top.loop_or_ret = pc+1;
} else {
stack_top.count = 1;
}
if(Debug) {
// Simple sanity check for provided type info ti:
// The declared size of the object must be not larger than the actual size
// (it can be smaller due to inferior pointers).
// It's difficult to make a comprehensive check due to inferior pointers,
// reflection, gob, etc.
if(pc[0] > n) {
runtime·printf("invalid gc type info: type info size %p, block size %p\n", pc[0], n);
runtime·throw("invalid gc type info");
}
}
} else if(UseSpanType) {
if(CollectStats)
runtime·xadd64(&gcstats.obj.notype, 1);
type = runtime·gettype(b);
if(type != 0) {
if(CollectStats)
runtime·xadd64(&gcstats.obj.typelookup, 1);
t = (Type*)(type & ~(uintptr)(PtrSize-1));
switch(type & (PtrSize-1)) {
case TypeInfo_SingleObject:
pc = (uintptr*)t->gc;
precise_type = true; // type information about 'b' is precise
stack_top.count = 1;
stack_top.elemsize = pc[0];
break;
case TypeInfo_Array:
pc = (uintptr*)t->gc;
if(pc[0] == 0)
goto next_block;
precise_type = true; // type information about 'b' is precise
stack_top.count = 0; // 0 means an infinite number of iterations
stack_top.elemsize = pc[0];
stack_top.loop_or_ret = pc+1;
break;
case TypeInfo_Chan:
chan = (Hchan*)b;
chantype = (ChanType*)t;
chan_ret = nil;
pc = chanProg;
break;
default:
if(Debug > 1)
runtime·printf("scanblock %p %D type %p %S\n", b, (int64)n, type, *t->string);
runtime·throw("scanblock: invalid type");
return;
}
if(Debug > 1)
runtime·printf("scanblock %p %D type %p %S pc=%p\n", b, (int64)n, type, *t->string, pc);
} else {
pc = defaultProg;
if(Debug > 1)
runtime·printf("scanblock %p %D unknown type\n", b, (int64)n);
}
} else {
pc = defaultProg;
if(Debug > 1)
runtime·printf("scanblock %p %D no span types\n", b, (int64)n);
}
if(IgnorePreciseGC)
pc = defaultProg;
pc++;
stack_top.b = (uintptr)b;
end_b = (uintptr)b + n - PtrSize;
for(;;) {
if(CollectStats)
runtime·xadd64(&gcstats.instr[pc[0]], 1);
obj = nil;
objti = 0;
switch(pc[0]) {
case GC_PTR:
obj = *(void**)(stack_top.b + pc[1]);
objti = pc[2];
if(Debug > 2)
runtime·printf("gc_ptr @%p: %p ti=%p\n", stack_top.b+pc[1], obj, objti);
pc += 3;
if(Debug)
checkptr(obj, objti);
break;
case GC_SLICE:
sliceptr = (Slice*)(stack_top.b + pc[1]);
if(Debug > 2)
runtime·printf("gc_slice @%p: %p/%D/%D\n", sliceptr, sliceptr->array, (int64)sliceptr->len, (int64)sliceptr->cap);
if(sliceptr->cap != 0) {
obj = sliceptr->array;
// Can't use slice element type for scanning,
// because if it points to an array embedded
// in the beginning of a struct,
// we will scan the whole struct as the slice.
// So just obtain type info from heap.
}
pc += 3;
break;
case GC_APTR:
obj = *(void**)(stack_top.b + pc[1]);
if(Debug > 2)
runtime·printf("gc_aptr @%p: %p\n", stack_top.b+pc[1], obj);
pc += 2;
break;
case GC_STRING:
stringptr = (String*)(stack_top.b + pc[1]);
if(Debug > 2)
runtime·printf("gc_string @%p: %p/%D\n", stack_top.b+pc[1], stringptr->str, (int64)stringptr->len);
if(stringptr->len != 0)
markonly(stringptr->str);
pc += 2;
continue;
case GC_EFACE:
eface = (Eface*)(stack_top.b + pc[1]);
pc += 2;
if(Debug > 2)
runtime·printf("gc_eface @%p: %p %p\n", stack_top.b+pc[1], eface->type, eface->data);
if(eface->type == nil)
continue;
// eface->type
t = eface->type;
if((void*)t >= arena_start && (void*)t < arena_used) {
*sbuf.ptr.pos++ = (PtrTarget){t, 0};
if(sbuf.ptr.pos == sbuf.ptr.end)
flushptrbuf(&sbuf);
}
// eface->data
if(eface->data >= arena_start && eface->data < arena_used) {
if(t->size <= sizeof(void*)) {
if((t->kind & KindNoPointers))
continue;
obj = eface->data;
if((t->kind & ~KindNoPointers) == KindPtr) {
// Only use type information if it is a pointer-containing type.
// This matches the GC programs written by cmd/gc/reflect.c's
// dgcsym1 in case TPTR32/case TPTR64. See rationale there.
et = ((PtrType*)t)->elem;
if(!(et->kind & KindNoPointers))
objti = (uintptr)((PtrType*)t)->elem->gc;
}
} else {
obj = eface->data;
objti = (uintptr)t->gc;
}
}
break;
case GC_IFACE:
iface = (Iface*)(stack_top.b + pc[1]);
pc += 2;
if(Debug > 2)
runtime·printf("gc_iface @%p: %p/%p %p\n", stack_top.b+pc[1], iface->tab, nil, iface->data);
if(iface->tab == nil)
continue;
// iface->tab
if((void*)iface->tab >= arena_start && (void*)iface->tab < arena_used) {
*sbuf.ptr.pos++ = (PtrTarget){iface->tab, (uintptr)itabtype->gc};
if(sbuf.ptr.pos == sbuf.ptr.end)
flushptrbuf(&sbuf);
}
// iface->data
if(iface->data >= arena_start && iface->data < arena_used) {
t = iface->tab->type;
if(t->size <= sizeof(void*)) {
if((t->kind & KindNoPointers))
continue;
obj = iface->data;
if((t->kind & ~KindNoPointers) == KindPtr) {
// Only use type information if it is a pointer-containing type.
// This matches the GC programs written by cmd/gc/reflect.c's
// dgcsym1 in case TPTR32/case TPTR64. See rationale there.
et = ((PtrType*)t)->elem;
if(!(et->kind & KindNoPointers))
objti = (uintptr)((PtrType*)t)->elem->gc;
}
} else {
obj = iface->data;
objti = (uintptr)t->gc;
}
}
break;
case GC_DEFAULT_PTR:
while(stack_top.b <= end_b) {
obj = *(byte**)stack_top.b;
if(Debug > 2)