Test ability to access unwritten-to mmap data in core file

gdb/testsuite/ChangeLog:

	PR corefiles/25631
	* gdb.base/corefile.exp (accessing anonymous, unwritten-to mmap data):
	New test.
	* gdb.base/coremaker.c (buf3): New global.
	(mmapdata): Add mmap call which uses MAP_ANONYMOUS and MAP_PRIVATE
	flags.

gdb/testsuite/ChangeLog

@@ -1,4 +1,13 @@
-2020-07-20  Kevin Buettner  <kevinb@redhat.com>
+2020-07-22  Kevin Buettner  <kevinb@redhat.com>
+
+	PR corefiles/25631
+	* gdb.base/corefile.exp (accessing anonymous, unwritten-to mmap data):
+	New test.
+	* gdb.base/coremaker.c (buf3): New global.
+	(mmapdata): Add mmap call which uses MAP_ANONYMOUS and MAP_PRIVATE
+	flags.
+
+2020-07-22  Kevin Buettner  <kevinb@redhat.com>
 
 	* gdb.base/coremaker.c (filler_ro): New global constant.
 

gdb/testsuite/gdb.base/corefile.exp

@@ -175,6 +175,15 @@ gdb_test_multiple "x/8bd buf2" "$test" {
     }
 }
 
+# Test ability to read anonymous and, more importantly, unwritten-to
+# mmap'd data.
+
+if { ![istarget *-linux*] } {
+    setup_xfail "*-*-*"
+}
+gdb_test "x/wx buf3" "$hex:\[ \t\]+0x00000000" \
+	 "accessing anonymous, unwritten-to mmap data"
+
 # test reinit_frame_cache
 
 gdb_load ${binfile}

gdb/testsuite/gdb.base/coremaker.c

@@ -38,6 +38,7 @@
 
 char *buf1;
 char *buf2;
+char *buf3;
 
 int coremaker_data = 1;	/* In Data section */
 int coremaker_bss;	/* In BSS section */
@@ -104,6 +105,15 @@ mmapdata ()
     }
   /* Touch buf2 so kernel writes it out into 'core'. */
   buf2[0] = buf1[0];
+
+  /* Create yet another region which is allocated, but not written to.  */
+  buf3 = mmap (NULL, MAPSIZE, PROT_READ | PROT_WRITE,
+               MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  if (buf3 == (char *) -1)
+    {
+      perror ("mmap failed");
+      return;
+    }
 }
 
 void