bug#50453: 27.2; Portable dumper broken on MSW

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: 50453@debbugs.gnu.org
> Date: Sat, 11 Sep 2021 10:57:12 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Please try the patch below.
> 
> Thanks.  Emacs correctly loads the dump file with that patch in place.

Great, thanks for testing.

Daniel, any comments to that patch (copied below for your
convenience)?

And while at that, can you tell why we request
DUMP_MEMORY_ACCESS_READWRITE and not DUMP_MEMORY_ACCESS_READ when
loading from the pdumper file?  Do we expect the need to change values
loaded from the file?

Here's the patch I was talking about, it is needed for supporting
FILE_MAP_COPY flag in the MapViewOfFileEx call on Windows 9X:

diff --git a/src/pdumper.c b/src/pdumper.c
index 7730ea3..2291fce 100644
--- a/src/pdumper.c
+++ b/src/pdumper.c
@@ -4537,15 +4537,28 @@ dump_map_file_w32 (void *base, int fd, off_t offset, 
size_t size,
   uint32_t offset_low = (uint32_t) (full_offset & 0xffffffff);
 
   int error;
+  DWORD protect;
   DWORD map_access;
 
   file = (HANDLE) _get_osfhandle (fd);
   if (file == INVALID_HANDLE_VALUE)
     goto out;
 
+  switch (protection)
+    {
+    case DUMP_MEMORY_ACCESS_READWRITE:
+      protect = PAGE_WRITECOPY;        /* for Windows 9X */
+      break;
+    default:
+    case DUMP_MEMORY_ACCESS_NONE:
+    case DUMP_MEMORY_ACCESS_READ:
+      protect = PAGE_READONLY;
+      break;
+    }
+
   section = CreateFileMapping (file,
                               /*lpAttributes=*/NULL,
-                              PAGE_READONLY,
+                              protect,
                               /*dwMaximumSizeHigh=*/0,
                               /*dwMaximumSizeLow=*/0,
                               /*lpName=*/NULL);