runtime: fix 32-bit malloc for pointers >= 0x80000000

The spans array is allocated in runtime·mallocinit.  On a
32-bit system the number of entries in the spans array is
MaxArena32 / PageSize, which (2U << 30) / (1 << 12) == (1 << 19).
So we are allocating an array that can hold 19 bits for an
index that can hold 20 bits.  According to the comment in the
function, this is intentional: we only allocate enough spans
(and bitmaps) for a 2G arena, because allocating more would
probably be wasteful.

But since the span index is simply the upper 20 bits of the
memory address, this scheme only works if memory addresses are
limited to the low 2G of memory.  That would be OK if we were
careful to enforce it, but we're not.  What we are careful to
enforce, in functions like runtime·MHeap_SysAlloc, is that we
always return addresses between the heap's arena_start and
arena_start + MaxArena32.

We generally get away with it because we start allocating just
after the program end, so we only run into trouble with
programs that allocate a lot of memory, enough to get past
address 0x80000000.

This changes the code that computes a span index to subtract
arena_start on 32-bit systems just as we currently do on
64-bit systems.

R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/49460043

diff --git a/src/pkg/runtime/malloc.goc b/src/pkg/runtime/malloc.goc
index 9a25029586d6ed127bd64412632db69feab3079e..f83e498293f24b91ae2a3be3a6e6c45f977c0b2e 100644 (file)
--- a/src/pkg/runtime/malloc.goc
+++ b/src/pkg/runtime/malloc.goc
@@ -593,8 +593,7 @@ runtime·settype_flush(M *mp)
 
                // (Manually inlined copy of runtime·MHeap_Lookup)
                p = (uintptr)v>>PageShift;
-               if(sizeof(void*) == 8)
-                       p -= (uintptr)runtime·mheap.arena_start >> PageShift;
+               p -= (uintptr)runtime·mheap.arena_start >> PageShift;
                s = runtime·mheap.spans[p];
 
                if(s->sizeclass == 0) {

diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 8014fe4689390303351f7f81b6f2ccdbbeb3d2bd..9b7d013700399ccc17db5846feed23ffa5bab217 100644 (file)
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -292,8 +292,7 @@ markonly(void *obj)
        // (Manually inlined copy of MHeap_LookupMaybe.)
        k = (uintptr)obj>>PageShift;
        x = k;
-       if(sizeof(void*) == 8)
-               x -= (uintptr)runtime·mheap.arena_start>>PageShift;
+       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;
@@ -492,8 +491,7 @@ flushptrbuf(Scanbuf *sbuf)
                // (Manually inlined copy of MHeap_LookupMaybe.)
                k = (uintptr)obj>>PageShift;
                x = k;
-               if(sizeof(void*) == 8)
-                       x -= (uintptr)arena_start>>PageShift;
+               x -= (uintptr)arena_start>>PageShift;
                s = runtime·mheap.spans[x];
                if(s == nil || k < s->start || obj >= s->limit || s->state != MSpanInUse)
                        continue;
@@ -540,8 +538,7 @@ flushptrbuf(Scanbuf *sbuf)
                // Ask span about size class.
                // (Manually inlined copy of MHeap_Lookup.)
                x = (uintptr)obj >> PageShift;
-               if(sizeof(void*) == 8)
-                       x -= (uintptr)arena_start>>PageShift;
+               x -= (uintptr)arena_start>>PageShift;
                s = runtime·mheap.spans[x];
 
                PREFETCH(obj);
@@ -658,8 +655,7 @@ checkptr(void *obj, uintptr objti)
        if(t == nil)
                return;
        x = (uintptr)obj >> PageShift;
-       if(sizeof(void*) == 8)
-               x -= (uintptr)(runtime·mheap.arena_start)>>PageShift;
+       x -= (uintptr)(runtime·mheap.arena_start)>>PageShift;
        s = runtime·mheap.spans[x];
        objstart = (byte*)((uintptr)s->start<<PageShift);
        if(s->sizeclass != 0) {

diff --git a/src/pkg/runtime/mheap.c b/src/pkg/runtime/mheap.c
index 1a926a413b3efa0c2e924101af4dce355df2e982..c77772afbe5c6e0d3dbd140ea8f9bf6171d65984 100644 (file)
--- a/src/pkg/runtime/mheap.c
+++ b/src/pkg/runtime/mheap.c
@@ -74,8 +74,7 @@ runtime·MHeap_MapSpans(MHeap *h)
 
        // Map spans array, PageSize at a time.
        n = (uintptr)h->arena_used;
-       if(sizeof(void*) == 8)
-               n -= (uintptr)h->arena_start;
+       n -= (uintptr)h->arena_start;
        n = n / PageSize * sizeof(h->spans[0]);
        n = ROUND(n, PageSize);
        if(h->spans_mapped >= n)
@@ -169,8 +168,7 @@ HaveSpan:
                runtime·MSpan_Init(t, s->start + npage, s->npages - npage);
                s->npages = npage;
                p = t->start;
-               if(sizeof(void*) == 8)
-                       p -= ((uintptr)h->arena_start>>PageShift);
+               p -= ((uintptr)h->arena_start>>PageShift);
                if(p > 0)
                        h->spans[p-1] = s;
                h->spans[p] = t;
@@ -188,8 +186,7 @@ HaveSpan:
        s->elemsize = (sizeclass==0 ? s->npages<<PageShift : runtime·class_to_size[sizeclass]);
        s->types.compression = MTypes_Empty;
        p = s->start;
-       if(sizeof(void*) == 8)
-               p -= ((uintptr)h->arena_start>>PageShift);
+       p -= ((uintptr)h->arena_start>>PageShift);
        for(n=0; n<npage; n++)
                h->spans[p+n] = s;
        return s;
@@ -257,8 +254,7 @@ MHeap_Grow(MHeap *h, uintptr npage)
        s = runtime·FixAlloc_Alloc(&h->spanalloc);
        runtime·MSpan_Init(s, (uintptr)v>>PageShift, ask>>PageShift);
        p = s->start;
-       if(sizeof(void*) == 8)
-               p -= ((uintptr)h->arena_start>>PageShift);
+       p -= ((uintptr)h->arena_start>>PageShift);
        h->spans[p] = s;
        h->spans[p + s->npages - 1] = s;
        s->state = MSpanInUse;
@@ -275,8 +271,7 @@ runtime·MHeap_Lookup(MHeap *h, void *v)
        uintptr p;
        
        p = (uintptr)v;
-       if(sizeof(void*) == 8)
-               p -= (uintptr)h->arena_start;
+       p -= (uintptr)h->arena_start;
        return h->spans[p >> PageShift];
 }
 
@@ -297,8 +292,7 @@ runtime·MHeap_LookupMaybe(MHeap *h, void *v)
                return nil;
        p = (uintptr)v>>PageShift;
        q = p;
-       if(sizeof(void*) == 8)
-               q -= (uintptr)h->arena_start >> PageShift;
+       q -= (uintptr)h->arena_start >> PageShift;
        s = h->spans[q];
        if(s == nil || p < s->start || v >= s->limit || s->state != MSpanInUse)
                return nil;
@@ -345,8 +339,7 @@ MHeap_FreeLocked(MHeap *h, MSpan *s)
 
        // Coalesce with earlier, later spans.
        p = s->start;
-       if(sizeof(void*) == 8)
-               p -= (uintptr)h->arena_start >> PageShift;
+       p -= (uintptr)h->arena_start >> PageShift;
        if(p > 0 && (t = h->spans[p-1]) != nil && t->state != MSpanInUse) {
                if(t->npreleased == 0) {  // cant't touch this otherwise
                        tp = (uintptr*)(t->start<<PageShift);