On 07/19/2017 06:51 PM, Andreas Schwab wrote:
>> emacs25 currently fails to build from source on m68k because the struct
>> Lisp_Object in src/lisp.h has incorrect alignment which results in the
>> tagged pointers used by the Lisp VM being corrupted. This happens because
>> the native alignment on m68k is 16-bit such that the total size of
>> List_Object
>> is not dividable by 8.
>
> That cannot be the source of the problem since Lisp_Object is not 8-byte
> aligned on any 32-bit platform.
Quoting Michael Karcher who tracked down the issue:
"sizeof(struct Lisp_Symbol) is 22 bytes on m68k, but the code expects the
size of the object to be dividable by 8."
And from src/lisp.h:
/***** Select the tagging scheme. *****/
/* The following option controls the tagging scheme:
- USE_LSB_TAG means that we can assume the least 3 bits of pointers are
always 0, and we can thus use them to hold tag bits, without
restricting our addressing space.
If ! USE_LSB_TAG, then use the top 3 bits for tagging, thus
restricting our possible address range.
USE_LSB_TAG not only requires the least 3 bits of pointers returned by
malloc to be 0 but also needs to be able to impose a mult-of-8 alignment
on the few static Lisp_Objects used: lispsym, all the defsubr, and
the two special buffers buffer_defaults and buffer_local_symbols. */
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaub...@debian.org
`. `' Freie Universitaet Berlin - glaub...@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
