emacs-27 888ffd9: Fix unexec failure on macOS 10.15.4

[YAMAMOTO Mitsuharu]

branch: emacs-27
commit 888ffd960c06d56a409a7ff15b1d930d25c56089
Author: YAMAMOTO Mitsuharu <address@hidden>
Commit: YAMAMOTO Mitsuharu <address@hidden>

    Fix unexec failure on macOS 10.15.4
    
    * src/unexmacosx.c (unexec_regions_merge): Align region start addresses to
    page boundaries and then merge regions.
---
 src/unexmacosx.c | 47 ++++++++++++++++++++++++-----------------------
 1 file changed, 24 insertions(+), 23 deletions(-)

diff --git a/src/unexmacosx.c b/src/unexmacosx.c
index 8d13241..59cbe3c 100644
--- a/src/unexmacosx.c
+++ b/src/unexmacosx.c
@@ -503,22 +503,34 @@ unexec_regions_sort_compare (const void *a, const void *b)
 static void
 unexec_regions_merge (void)
 {
-  int i, n;
-  unexec_region_info r;
-  vm_size_t padsize;
-
   qsort (unexec_regions, num_unexec_regions, sizeof (unexec_regions[0]),
         &unexec_regions_sort_compare);
-  n = 0;
-  r = unexec_regions[0];
-  padsize = r.range.address & (pagesize - 1);
-  if (padsize)
+
+  /* Align each region start address to a page boundary.  */
+  for (unexec_region_info *cur = unexec_regions;
+       cur < unexec_regions + num_unexec_regions; cur++)
     {
-      r.range.address -= padsize;
-      r.range.size += padsize;
-      r.filesize += padsize;
+      vm_size_t padsize = cur->range.address & (pagesize - 1);
+      if (padsize)
+       {
+         cur->range.address -= padsize;
+         cur->range.size += padsize;
+         cur->filesize += padsize;
+
+         unexec_region_info *prev = cur == unexec_regions ? NULL : cur - 1;
+         if (prev
+             && prev->range.address + prev->range.size > cur->range.address)
+           {
+             prev->range.size = cur->range.address - prev->range.address;
+             if (prev->filesize > prev->range.size)
+               prev->filesize = prev->range.size;
+           }
+       }
     }
-  for (i = 1; i < num_unexec_regions; i++)
+
+  int n = 0;
+  unexec_region_info r = unexec_regions[0];
+  for (int i = 1; i < num_unexec_regions; i++)
     {
       if (r.range.address + r.range.size == unexec_regions[i].range.address
          && r.range.size - r.filesize < 2 * pagesize)
@@ -530,17 +542,6 @@ unexec_regions_merge (void)
        {
          unexec_regions[n++] = r;
          r = unexec_regions[i];
-         padsize = r.range.address & (pagesize - 1);
-         if (padsize)
-           {
-             if ((unexec_regions[n-1].range.address
-                  + unexec_regions[n-1].range.size) == r.range.address)
-               unexec_regions[n-1].range.size -= padsize;
-
-             r.range.address -= padsize;
-             r.range.size += padsize;
-             r.filesize += padsize;
-           }
        }
     }
   unexec_regions[n++] = r;