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Lines 324-330
static void* ComputeRandomAllocationAddress() {
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// x64 CPUs have a 48-bit address space and on some platforms the OS will |
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// x64 CPUs have a 48-bit address space and on some platforms the OS will |
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// give us access to 47 bits, so to be safe we right shift by 18 to leave |
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// give us access to 47 bits, so to be safe we right shift by 18 to leave |
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// 46 bits. |
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// 46 bits. |
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# ifdef __ia64__ |
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// On ia64 virtual address space looks like one of: |
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// virt_addr_64 = [ <63..61> | <unimplemented> | L3 | L2 | L1 | offset ] |
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// virt_addr_64 = [ <63..61> | <unimplemented> | L4 | L3 | L2 | L1 | offset ] |
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// where L{1..L4} are page tables. Each page table (except top-level L3 or L4) |
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// is itself a page-size entry and can store PageSize / 8 entries. Top-level |
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// entry is 1/8 of of L1/L2 (as 3 upper bits are part of <63..61> address part). |
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// Note: that makes addressable size directly depend on page size. |
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// |
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// We conservatively assume 3 levels of page tables here. This makes the |
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// following formula: |
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// L3 = log2(PAGE / 8 / 8) = log2(PAGE / 8) - 3 |
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// L2 = log2(PAGE / 8) |
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// L1 = log2(PAGE / 8) |
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// offset = log2(PAGE) = log2(PAGE / 8) + 3 |
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// thus |
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// L3 + L2 + L1 + offset = 4 * log2(PAGE / 8) |
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// For more details see http://www.ia64-linux.org/doc/IA64linuxkernel.PDF |
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// (slide 19: "user regions"). |
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static uint64_t ia64_virt_bits = std::min<uint64_t>( |
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4 * (mozilla::FloorLog2(gc::SystemPageSize() / 8)), |
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46); |
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rand >>= (64 - ia64_virt_bits); |
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# else |
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rand >>= 18; |
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rand >>= 18; |
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# endif |
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# else |
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# else |
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// On 32-bit, right shift by 34 to leave 30 bits, range [0, 1GiB). Then add |
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// On 32-bit, right shift by 34 to leave 30 bits, range [0, 1GiB). Then add |
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// 512MiB to get range [512MiB, 1.5GiB), or [0x20000000, 0x60000000). This |
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// 512MiB to get range [512MiB, 1.5GiB), or [0x20000000, 0x60000000). This |
