This is because even on x64, V8-internal pointers are 32-bit and objects are 4 byte aligned, due to pointer compression (https://v8.dev/blog/pointer-compression)
On Monday, December 4, 2023 at 4:17:02 PM UTC-8 thisis...@gmail.com wrote: > Hi, all! > > By reading the document (https://v8.dev/blog/pointer-compression), it is > saying that "V8 always allocates objects in the heap at word-aligned > addresses, which allows it to use the 2 (or 3, depending on the machine > word size) least significant bits for tagging." > > Since V8 already uses the last 2 lsbs, for the x64 machine, I think I can > use the 3rd lsb to store other pointer information (as on x64 machine, the > object address should be 8 bytes aligned). > > However, I found that even on an x64 machine, the object allocated on the > heap is not necessarily 8-byte aligned as the third lsb bit is not always > zero. For example, > > let e = function () { return "Hello World!"; }; %DebugPrint(e); > DebugPrint: 0x2bba0024aa7d: [Function] - map: 0x2bba0010439d > <Map[32](HOLEY_ELEMENTS)> [FastProperties] - prototype: 0x2bba001042c5 > <JSFunction (sfi = 0x2bba000c9405)> - elements: 0x2bba000006a5 > <FixedArray[0]> [HOLEY_ELEMENTS] - function prototype: - initial_map: - > shared_info: 0x2bba00119ced <SharedFunctionInfo e> - name: 0x2bba000029e9 > <String[1]: #e> - builtin: CompileLazy - formal_parameter_count: 0 - kind: > NormalFunction - context: 0x2bba00119dcd <ScriptContext[3]> - code: > 0x2bba0030efdd <Code BUILTIN CompileLazy> - source code: () { return "Hello > World!"; } > > The address ends with 0xd (1101), indicating the heap chunk's address ends > with 0xC. I wonder why the object address is not 8-bytes aligned (should > always end with 0x0 or 0x8)? > -- -- v8-users mailing list v8-users@googlegroups.com http://groups.google.com/group/v8-users --- You received this message because you are subscribed to the Google Groups "v8-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to v8-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/v8-users/77fe0783-87fe-45df-8bdd-ee9b7943c7e6n%40googlegroups.com.
