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)?
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