39 //
40 // A "good" base is, in this order:
41 // 1) only bits in A; this would be an address < 4KB, which is unrealistic on normal Linux boxes since
42 // the typical default for vm.mmap_min_address is 64KB. We ignore that.
43 // 2) only bits in B: a 12-bit-aligned address below 4GB. 12 bit = 4KB, but since mmap reserves at
44 // page boundaries, we can ignore the alignment.
45 // 3) only bits in C: a 4GB-aligned address that is lower than 16TB.
46 // 4) only bits in D: a 16TB-aligned address.
47
48 // First, attempt to allocate < 4GB. We do this unconditionally:
49 // - if can_optimize_for_zero_base, a <4GB mapping start would allow us to run unscaled (base = 0, shift = 0)
50 // - if !can_optimize_for_zero_base, a <4GB mapping start is still good, the resulting immediate can be encoded
51 // with one instruction (2)
52 result = reserve_address_space_for_unscaled_encoding(size, aslr);
53
54 // Failing that, attempt to reserve for base=zero shift>0
55 if (result == nullptr && optimize_for_zero_base) {
56 result = reserve_address_space_for_zerobased_encoding(size, aslr);
57 }
58
59 // Failing that, optimize for case (3) - a base with only bits set between [33-44)
60 if (result == nullptr) {
61 const uintptr_t from = nth_bit(32 + (optimize_for_zero_base ? LogKlassAlignmentInBytes : 0));
62 constexpr uintptr_t to = nth_bit(44);
63 constexpr size_t alignment = nth_bit(32);
64 result = reserve_address_space_X(from, to, size, alignment, aslr);
65 }
66
67 // Failing that, optimize for case (4) - a base with only bits set between [44-64)
68 if (result == nullptr) {
69 constexpr uintptr_t from = nth_bit(44);
70 constexpr uintptr_t to = UINT64_MAX;
71 constexpr size_t alignment = nth_bit(44);
72 result = reserve_address_space_X(from, to, size, alignment, aslr);
73 }
74
75 return result;
76 }
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39 //
40 // A "good" base is, in this order:
41 // 1) only bits in A; this would be an address < 4KB, which is unrealistic on normal Linux boxes since
42 // the typical default for vm.mmap_min_address is 64KB. We ignore that.
43 // 2) only bits in B: a 12-bit-aligned address below 4GB. 12 bit = 4KB, but since mmap reserves at
44 // page boundaries, we can ignore the alignment.
45 // 3) only bits in C: a 4GB-aligned address that is lower than 16TB.
46 // 4) only bits in D: a 16TB-aligned address.
47
48 // First, attempt to allocate < 4GB. We do this unconditionally:
49 // - if can_optimize_for_zero_base, a <4GB mapping start would allow us to run unscaled (base = 0, shift = 0)
50 // - if !can_optimize_for_zero_base, a <4GB mapping start is still good, the resulting immediate can be encoded
51 // with one instruction (2)
52 result = reserve_address_space_for_unscaled_encoding(size, aslr);
53
54 // Failing that, attempt to reserve for base=zero shift>0
55 if (result == nullptr && optimize_for_zero_base) {
56 result = reserve_address_space_for_zerobased_encoding(size, aslr);
57 }
58
59 // Failing that, optimize for case (3) - a base with only bits set between [32-44)
60 if (result == nullptr) {
61 const uintptr_t from = nth_bit(32);
62 constexpr uintptr_t to = nth_bit(44);
63 constexpr size_t alignment = nth_bit(32);
64 result = reserve_address_space_X(from, to, size, alignment, aslr);
65 }
66
67 // Failing that, optimize for case (4) - a base with only bits set between [44-64)
68 if (result == nullptr) {
69 constexpr uintptr_t from = nth_bit(44);
70 constexpr uintptr_t to = UINT64_MAX;
71 constexpr size_t alignment = nth_bit(44);
72 result = reserve_address_space_X(from, to, size, alignment, aslr);
73 }
74
75 return result;
76 }
77
78 bool CompressedKlassPointers::pd_initialize(address addr, size_t len) { return false; }
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