abd471378c
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. From-SVN: r206501 |
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| boehm-gc | ||
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