Re: Segfault when initializing VLA cdata
- From: Mike Pall <mike-1503@xxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Tue, 10 Mar 2015 12:58:16 +0100
Cheyi Lin wrote:
> > Byte arrays may also be initialized with a Lua string.
> > This copies the whole string plus a terminating zero-byte.
> > The copy stops early only if the array has a known, fixed size.
>
> a) why it crashes only with a Lua string which the length is multiple of 8
> bytes?
Because the byte that's overwritten by the zero terminator is not
unused in this case.
> b) why 'local r = ffi.new("uint8_t[?]", #s, s)' is not equivalent to 'local
> r = ffi.new("uint8_t[?]", #s); ffi.copy(r, s, #s)'?
A VLA is NOT considered as having a fixed size, so the copy does
NOT stop early. It copies #s+1 bytes, including the zero
terminator, which writes beyond the end of the array.
--Mike
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