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armv5 devices and older (i.e. <= arm9 generation) require addresses that are stored to and loaded from to to be 4-byte aligned. If this is not the case the lower 2 bits of the address are cleared and the load is performed in an unexpected order, including up to 3 bytes of data located prior to the address. Inlined buckets are stored after their key in a page and since there is no guarantee that the key will be of a length that is a multiple of 4, it is possible for unaligned load/stores to occur when they are cast back to bucket and page pointer types. The fix adds a new field to track whether the current architecture exhibits this issue, sets it on module load for ARM architectures, and then on bucket open, if this field is set and the address is unaligned, a byte-by-byte copy of the inlined bucket is performed. Ref: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka15414.html
29 lines
831 B
Go
29 lines
831 B
Go
package bolt
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import "unsafe"
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// maxMapSize represents the largest mmap size supported by Bolt.
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const maxMapSize = 0x7FFFFFFF // 2GB
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// maxAllocSize is the size used when creating array pointers.
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const maxAllocSize = 0xFFFFFFF
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// Are unaligned load/stores broken on this arch?
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var brokenUnaligned bool
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func init() {
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// Simple check to see whether this arch handles unaligned load/stores
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// correctly.
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// ARM9 and older devices require load/stores to be from/to aligned
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// addresses. If not, the lower 2 bits are cleared and that address is
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// read in a jumbled up order.
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// See http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka15414.html
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raw := [6]byte{0xfe, 0xef, 0x11, 0x22, 0x22, 0x11}
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val := *(*uint32)(unsafe.Pointer(uintptr(unsafe.Pointer(&raw)) + 2))
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brokenUnaligned = val != 0x11222211
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}
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