On 2/15/2018 9:36 PM, Daniel Colascione wrote:
On 02/15/2018 05:56 PM, Ken Brown wrote:
On 2/15/2018 6:36 PM, Daniel Colascione wrote:
On Feb 15, 2018 3:31 PM, Ken Brown <address@hidden> wrote:
[...]
I just tried to build on 64-bit Cygwin, and the build fails as
follows:
[...]
Dumping under the name bootstrap-emacs.pdmp
dumping fingerprint:
923050a9f611ad7ead76eea704308e4d05f152601a9134cf8d1b5ff3e0e1a986
Dump complete
Byte counts: header=80 hot=13187392 discardable=119424 cold=9086640
Reloc counts: hot=919268 discardable=5790
make -C ../lisp compile-first EMACS="../src/bootstrap-emacs.exe"
make[2]: Entering directory
'/home/kbrown/src/emacs/x86_64-pdumper/lisp'
ELC ../../pdumper/lisp/emacs-lisp/macroexp.elc
ELC ../../pdumper/lisp/emacs-lisp/cconv.elc
ELC ../../pdumper/lisp/emacs-lisp/byte-opt.elc
ELC ../../pdumper/lisp/emacs-lisp/bytecomp.elc
emacs: could not load dump file "../src/bootstrap-emacs.pdmp": out
of memory
There's probably some obvious explanation, but I don't see it at
the
moment.
I'm not entirely surprised to see Cygwin fall over here. We could
just use the Windows memory mapping functions directly, but I'd
prefer to stick with the POSIX API if we can make it work.
I agree.
Any idea where in the mmap sequence we fail?
I haven't looked at the code yet, so I don't understand the question.
If you give me some guidance, I'll try to investigate.
Thanks. I think the trouble must be in dump_mmap_contiguous. We report
all errors from this function as "out of memory". dump_mmap_contiguous
takes an array of mapping descriptors (think ELF segments or
something) and maps them all into a single contiguous region of
virtual memory. On POSIX systems, we reserve a chunk of address space
with a big PROT_NONE anonymous mapping, then carve it up into the
separate mappings that we really want. Windows doesn't support atomic
mmap replacement, so Cygwin has to emulate it, and I wouldn't be
surprised if something's going wrong in this emulation.
You're right that the problem is in dump_mmap_contiguous. I stepped
through it in gdb and found the following:
1. The call to dump_anonymous_allocate at pdumper.c:4432 succeeds.
2. We enter the loop at pdumper.c:4451 with i = 0. dump_map_file is
called, which calls dump_map_file_posix with protection =
DUMP_MEMORY_ACCESS_READWRITE.
3. This calls mmap at line 4219 with mem_prot = PROT_READ | PROT_WRITE
and mem_flags = MAP_PRIVATE | MAP_FIXED.
4. This mmap call fails.
I don't know if this is a bug in Cygwin's mmap or simply a limitation
that has to be worked around. Should I take this to the Cygwin mailing
list, or do you have other ideas as to how to proceed?