gdb: silence some 'Can't open file' warnings from core file loading

diff --git a/gdb/corelow.c b/gdb/corelow.c
index 59c16677109..213b53808bd 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -540,11 +540,41 @@  core_target::build_file_mappings ()
 	  /* If ABFD was opened, but the wrong format, close it now.  */
 	  abfd = nullptr;
 
+	  /* When true, this indicates that the mapped contents of this
+	     file are available within the core file.  When false, some of
+	     the mapped contents are not available.  If the contents are
+	     available within the core file, then we don't need to warn
+	     the user if the file is no longer available.  */
+	  bool content_is_in_core_file_p = true;
+
 	  /* Record all regions for this file as unavailable.  */
 	  for (const mapped_file::region &region : file_data.regions)
-	    m_core_unavailable_mappings.emplace_back (region.start,
-						      region.end
-						      - region.start);
+	    {
+	      /* Check to see if the region is available within the core
+		 file.  */
+	      bool found_region_in_core_file = false;
+	      for (const target_section &ts : m_core_section_table)
+		{
+		  if (ts.addr <= region.start && ts.endaddr >= region.end
+		      && (ts.the_bfd_section->flags & SEC_HAS_CONTENTS) != 0)
+		    {
+		      found_region_in_core_file = true;
+		      break;
+		    }
+		}
+
+	      /* This region is not available within the core file.
+		 Without the file available to read from it is not possible
+		 for GDB to read this mapping within the inferior.  Warn
+		 the user about this case.  */
+	      if (!found_region_in_core_file)
+		content_is_in_core_file_p = false;
+
+	      /* Record the unavailable region.  */
+	      m_core_unavailable_mappings.emplace_back (region.start,
+							region.end
+							- region.start);
+	    }
 
 	  /* And give the user an appropriate warning.  */
 	  if (build_id_mismatch)
@@ -564,7 +594,7 @@  core_target::build_file_mappings ()
 			 styled_string (file_name_style.style (),
 					expanded_fname.get ()));
 	    }
-	  else
+	  else if (!content_is_in_core_file_p)
 	    {
 	      if (expanded_fname == nullptr
 		  || filename == expanded_fname.get ())
diff --git a/gdb/testsuite/gdb.base/corefile3.c b/gdb/testsuite/gdb.base/corefile3.c
new file mode 100644
index 00000000000..16030dd017c
--- /dev/null
+++ b/gdb/testsuite/gdb.base/corefile3.c
@@ -0,0 +1,118 @@ 
+/* Copyright 1992-2025 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* This file is based on coremaker.c.  */
+
+#include <stdio.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <assert.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+
+#define MAPSIZE (8 * 1024)
+
+/* Global pointers so it's easier to access them from GDB.  */
+
+char *rw_mapping = NULL;
+char *malloc_buffer = NULL;
+char *anon_mapping = NULL;
+char *shm_mapping = NULL;
+
+/* Create mappings within this process.  */
+
+void
+mmapdata ()
+{
+  /* Allocate and initialize a buffer that will be used to write the file
+     that is later mapped in.  */
+
+  malloc_buffer = (char *) malloc (MAPSIZE);
+  for (int j = 0; j < MAPSIZE; ++j)
+    malloc_buffer[j] = j;
+
+  /* Write the file to map in.  */
+
+  int fd = open ("coremmap.data", O_CREAT | O_RDWR, 0666);
+  assert (fd != -1);
+  write (fd, malloc_buffer, MAPSIZE);
+
+  /* Now map the file into our address space as RW_MAPPING.  */
+
+  rw_mapping
+    = (char *) mmap (0, MAPSIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+  assert (rw_mapping != (char *) MAP_FAILED);
+
+  /* Verify that the original data and the mapped data are identical.  If
+     not, we'd rather fail now than when trying to access the mapped data
+     from the core file. */
+
+  for (int j = 0; j < MAPSIZE; ++j)
+    assert (malloc_buffer[j] == rw_mapping[j]);
+
+  /* Touch RW_MAPPING so the kernel writes it out into 'core'.  */
+  rw_mapping[0] = malloc_buffer[0];
+
+  /* Create yet another region which is allocated, but not written to.  */
+  anon_mapping = mmap (NULL, MAPSIZE, PROT_READ | PROT_WRITE,
+		       MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  assert (anon_mapping != MAP_FAILED);
+
+  /* Create a shared memory mapping.  */
+  int sid = shmget (IPC_PRIVATE, MAPSIZE, IPC_CREAT | IPC_EXCL | 0777);
+  assert (sid != -1);
+  shm_mapping = (char *) shmat (sid, NULL, 0);
+  int res = shmctl (sid, IPC_RMID, NULL);
+  assert (res == 0);
+  assert (shm_mapping != MAP_FAILED);
+}
+
+void
+func2 ()
+{
+#ifdef SA_FULLDUMP
+  /* Force a corefile that includes the data section for AIX.  */
+  {
+    struct sigaction sa;
+
+    sigaction (SIGABRT, (struct sigaction *)0, &sa);
+    sa.sa_flags |= SA_FULLDUMP;
+    sigaction (SIGABRT, &sa, (struct sigaction *)0);
+  }
+#endif
+
+  abort ();
+}
+
+void
+func1 ()
+{
+  func2 ();
+}
+
+int
+main (void)
+{
+  mmapdata ();
+  func1 ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/corefile3.exp b/gdb/testsuite/gdb.base/corefile3.exp
new file mode 100644
index 00000000000..08e417eec10
--- /dev/null
+++ b/gdb/testsuite/gdb.base/corefile3.exp
@@ -0,0 +1,73 @@ 
+# Copyright 2025 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Create a core file with some mapped regions, but ensure that the
+# types region mean that the kernel should write the region into the
+# core file (e.g. r/w file backed mapping).
+#
+# We then delete the file that backed the mapping and load the core
+# file into GDB.
+#
+# GDB shouldn't warn about the file being missing.  It doesn't matter;
+# the file contents can all be found in the core file itself.
+
+require isnative
+require {!is_remote host}
+
+standard_testfile
+
+if {[build_executable $testfile.exp $testfile $srcfile] == -1} {
+    return
+}
+
+# Do not delete coremap.data when calling core_find.  This file is
+# required for GDB to find mmap'd data in the "accessing read-only
+# mmapped data in core file" test.
+set corefile [core_find $binfile {}]
+if {$corefile == ""} {
+    return
+}
+
+# Move coremap.data file out of the way, so it cannot be found when we
+# later load the core file into GDB.
+set data_filename \
+    [standard_output_file coredir.[getpid]/coremmap.data]
+set backup_filename \
+    [standard_output_file coredir.[getpid]/coremmap.data.backup]
+remote_exec host "mv ${data_filename} ${backup_filename}"
+
+clean_restart $binfile
+
+# Load the core file.  The 'coremap.data' file cannot be found by GDB,
+# but all the mappings for that file are r/w and should be present in
+# the core file, so we shouldn't get any warnings from GDB about it.
+set warnings_seen 0
+gdb_test_multiple "core-file $corefile" "core-file command" {
+    -re "^warning: Can't open file \[^\r\n\]+ during file-backed mapping note processing\r\n" {
+	incr warnings_seen
+	exp_continue
+    }
+    -re "^$gdb_prompt $" {
+	gdb_assert { $warnings_seen == 0 } $gdb_test_name
+    }
+    -re "^\[^\r\n\]*\r\n" {
+	exp_continue
+    }
+}
+
+# Check the mappings are all readable.
+foreach label { rw_mapping malloc_buffer anon_mapping shm_mapping } {
+    gdb_test "x/1wd $label" "^$hex:\\s+$decimal"
+}