Implement support for checking /proc/PID/coredump_filter

This patch, as the subject says, extends GDB so that it is able to use
the contents of the file /proc/PID/coredump_filter when generating a
corefile.  This file contains a bit mask that is a representation of
the different types of memory mappings in the Linux kernel; the user
can choose to dump or not dump a certain type of memory mapping by
enabling/disabling the respective bit in the bit mask.  Currently,
here is what is supported:

  bit 0  Dump anonymous private mappings.
  bit 1  Dump anonymous shared mappings.
  bit 2  Dump file-backed private mappings.
  bit 3  Dump file-backed shared mappings.
  bit 4 (since Linux 2.6.24)
         Dump ELF headers.
  bit 5 (since Linux 2.6.28)
         Dump private huge pages.
  bit 6 (since Linux 2.6.28)
         Dump shared huge pages.

(This table has been taken from core(5), but you can also read about it
on Documentation/filesystems/proc.txt inside the Linux kernel source
tree).

The default value for this file, used by the Linux kernel, is 0x33,
which means that bits 0, 1, 4 and 5 are enabled.  This is also the
default for GDB implemented in this patch, FWIW.

Well, reading the file is obviously trivial.  The hard part, mind you,
is how to determine the types of the memory mappings.  For that, I
extended the code of gdb/linux-tdep.c:linux_find_memory_regions_full and
made it rely *much more* on the information gathered from
/proc/<PID>/smaps.  This file contains a "verbose dump" of the
inferior's memory mappings, and we were not using as much information as
we could from it.  If you want to read more about this file, take a look
at the proc(5) manpage (I will also write a blog post soon about
everything I had to learn to get this patch done, and when I it is ready
I will post it here).

With Oleg Nesterov's help, we could improve the current algorithm for
determining whether a memory mapping is anonymous/file-backed,
private/shared.  GDB now also respects the MADV_DONTDUMP flag and does
not dump the memory mapping marked as so, and will always dump
"[vsyscall]" or "[vdso]" mappings (just like the Linux kernel).

In a nutshell, what the new code is doing is:

- If the mapping is associated to a file whose name ends with
  " (deleted)", or if the file is "/dev/zero", or if it is "/SYSV%08x"
  (shared memory), or if there is no file associated with it, or if
  the AnonHugePages: or the Anonymous: fields in the /proc/PID/smaps
  have contents, then GDB considers this mapping to be anonymous.
  There is a special case in this, though: if the memory mapping is a
  file-backed one, but *also* contains "Anonymous:" or
  "AnonHugePages:" pages, then GDB considers this mapping to be *both*
  anonymous and file-backed, just like the Linux kernel does.  What
  that means is simple: this mapping will be dumped if the user
  requested anonymous mappings *or* if the user requested file-backed
  mappings to be present in the corefile.

  It is worth mentioning that, from all those checks described above,
  the most fragile is the one to see if the file name ends with
  " (deleted)".  This does not necessarily mean that the mapping is
  anonymous, because the deleted file associated with the mapping may
  have been a hard link to another file, for example.  The Linux
  kernel checks to see if "i_nlink == 0", but GDB cannot easily do
  this check (as it has been discussed, GDB would need to run as root,
  and would need to check the contents of the /proc/PID/map_files/
  directory in order to determine whether the deleted was a hardlink
  or not).  Therefore, we made a compromise here, and we assume that
  if the file name ends with " (deleted)", then the mapping is indeed
  anonymous.  FWIW, this is something the Linux kernel could do
  better: expose this information in a more direct way.

- If we see the flag "sh" in the VmFlags: field (in /proc/PID/smaps),
  then certainly the memory mapping is shared (VM_SHARED).  If we have
  access to the VmFlags, and we don't see the "sh" there, then
  certainly the mapping is private.  However, older Linux kernels (see
  the code for more details) do not have the VmFlags field; in that
  case, we use another heuristic: if we see 'p' in the permission
  flags, then we assume that the mapping is private, even though the
  presence of the 's' flag there would mean VM_MAYSHARE, which means
  the mapping could still be private.  This should work OK enough,
  however.

Finally, it is worth mentioning that I added a new command, 'set
use-coredump-filter on/off'.  When it is 'on', it will read the
coredump_filter' file (if it exists) and use its value; otherwise, it
will use the default value mentioned above (0x33) to decide which memory
mappings to dump.

gdb/ChangeLog:
2015-03-31  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Oleg Nesterov  <oleg@redhat.com>

	PR corefiles/16092
	* linux-tdep.c: Include 'gdbcmd.h' and 'gdb_regex.h'.
	New enum identifying the various options of the coredump_filter
	file.
	(struct smaps_vmflags): New struct.
	(use_coredump_filter): New variable.
	(decode_vmflags): New function.
	(mapping_is_anonymous_p): Likewise.
	(dump_mapping_p): Likewise.
	(linux_find_memory_regions_full): New variables
	'coredumpfilter_name', 'coredumpfilterdata', 'pid', 'filterflags'.
	Removed variable 'modified'.  Read /proc/<PID>/smaps file; improve
	parsing of its information.  Implement memory mapping filtering
	based on its contents.
	(show_use_coredump_filter): New function.
	(_initialize_linux_tdep): New command 'set use-coredump-filter'.
	* NEWS: Mention the possibility of using the
	'/proc/PID/coredump_filter' file when generating a corefile.
	Mention new command 'set use-coredump-filter'.

gdb/doc/ChangeLog:
2015-03-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR corefiles/16092
	* gdb.texinfo (gcore): Mention new command 'set
	use-coredump-filter'.
	(set use-coredump-filter): Document new command.

gdb/testsuite/ChangeLog:
2015-03-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR corefiles/16092
	* gdb.base/coredump-filter.c: New file.
	* gdb.base/coredump-filter.exp: Likewise.

1 files changed, 427 insertions, 28 deletions

diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index ea0d4cd..4af1d01 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -35,9 +35,61 @@
 #include "observer.h"
 #include "objfiles.h"
 #include "infcall.h"
+#include "gdbcmd.h"
+#include "gdb_regex.h"
 
 #include <ctype.h>
 
+/* This enum represents the values that the user can choose when
+   informing the Linux kernel about which memory mappings will be
+   dumped in a corefile.  They are described in the file
+   Documentation/filesystems/proc.txt, inside the Linux kernel
+   tree.  */
+
+enum
+  {
+    COREFILTER_ANON_PRIVATE = 1 << 0,
+    COREFILTER_ANON_SHARED = 1 << 1,
+    COREFILTER_MAPPED_PRIVATE = 1 << 2,
+    COREFILTER_MAPPED_SHARED = 1 << 3,
+    COREFILTER_ELF_HEADERS = 1 << 4,
+    COREFILTER_HUGETLB_PRIVATE = 1 << 5,
+    COREFILTER_HUGETLB_SHARED = 1 << 6,
+  };
+
+/* This struct is used to map flags found in the "VmFlags:" field (in
+   the /proc/<PID>/smaps file).  */
+
+struct smaps_vmflags
+  {
+    /* Zero if this structure has not been initialized yet.  It
+       probably means that the Linux kernel being used does not emit
+       the "VmFlags:" field on "/proc/PID/smaps".  */
+
+    unsigned int initialized_p : 1;
+
+    /* Memory mapped I/O area (VM_IO, "io").  */
+
+    unsigned int io_page : 1;
+
+    /* Area uses huge TLB pages (VM_HUGETLB, "ht").  */
+
+    unsigned int uses_huge_tlb : 1;
+
+    /* Do not include this memory region on the coredump (VM_DONTDUMP, "dd").  */
+
+    unsigned int exclude_coredump : 1;
+
+    /* Is this a MAP_SHARED mapping (VM_SHARED, "sh").  */
+
+    unsigned int shared_mapping : 1;
+  };
+
+/* Whether to take the /proc/PID/coredump_filter into account when
+   generating a corefile.  */
+
+static int use_coredump_filter = 1;
+
 /* This enum represents the signals' numbers on a generic architecture
    running the Linux kernel.  The definition of "generic" comes from
    the file <include/uapi/asm-generic/signal.h>, from the Linux kernel
@@ -381,6 +433,248 @@ read_mapping (const char *line,
   *filename = p;
 }
 
+/* Helper function to decode the "VmFlags" field in /proc/PID/smaps.
+
+   This function was based on the documentation found on
+   <Documentation/filesystems/proc.txt>, on the Linux kernel.
+
+   Linux kernels before commit
+   834f82e2aa9a8ede94b17b656329f850c1471514 (3.10) do not have this
+   field on smaps.  */
+
+static void
+decode_vmflags (char *p, struct smaps_vmflags *v)
+{
+  char *saveptr;
+  const char *s;
+
+  v->initialized_p = 1;
+  p = skip_to_space (p);
+  p = skip_spaces (p);
+
+  for (s = strtok_r (p, " ", &saveptr);
+       s != NULL;
+       s = strtok_r (NULL, " ", &saveptr))
+    {
+      if (strcmp (s, "io") == 0)
+	v->io_page = 1;
+      else if (strcmp (s, "ht") == 0)
+	v->uses_huge_tlb = 1;
+      else if (strcmp (s, "dd") == 0)
+	v->exclude_coredump = 1;
+      else if (strcmp (s, "sh") == 0)
+	v->shared_mapping = 1;
+    }
+}
+
+/* Return 1 if the memory mapping is anonymous, 0 otherwise.
+
+   FILENAME is the name of the file present in the first line of the
+   memory mapping, in the "/proc/PID/smaps" output.  For example, if
+   the first line is:
+
+   7fd0ca877000-7fd0d0da0000 r--p 00000000 fd:02 2100770   /path/to/file
+
+   Then FILENAME will be "/path/to/file".  */
+
+static int
+mapping_is_anonymous_p (const char *filename)
+{
+  static regex_t dev_zero_regex, shmem_file_regex, file_deleted_regex;
+  static int init_regex_p = 0;
+
+  if (!init_regex_p)
+    {
+      struct cleanup *c = make_cleanup (null_cleanup, NULL);
+
+      /* Let's be pessimistic and assume there will be an error while
+	 compiling the regex'es.  */
+      init_regex_p = -1;
+
+      /* DEV_ZERO_REGEX matches "/dev/zero" filenames (with or
+	 without the "(deleted)" string in the end).  We know for
+	 sure, based on the Linux kernel code, that memory mappings
+	 whose associated filename is "/dev/zero" are guaranteed to be
+	 MAP_ANONYMOUS.  */
+      compile_rx_or_error (&dev_zero_regex, "^/dev/zero\\( (deleted)\\)\\?$",
+			   _("Could not compile regex to match /dev/zero "
+			     "filename"));
+      /* SHMEM_FILE_REGEX matches "/SYSV%08x" filenames (with or
+	 without the "(deleted)" string in the end).  These filenames
+	 refer to shared memory (shmem), and memory mappings
+	 associated with them are MAP_ANONYMOUS as well.  */
+      compile_rx_or_error (&shmem_file_regex,
+			   "^/\\?SYSV[0-9a-fA-F]\\{8\\}\\( (deleted)\\)\\?$",
+			   _("Could not compile regex to match shmem "
+			     "filenames"));
+      /* FILE_DELETED_REGEX is a heuristic we use to try to mimic the
+	 Linux kernel's 'n_link == 0' code, which is responsible to
+	 decide if it is dealing with a 'MAP_SHARED | MAP_ANONYMOUS'
+	 mapping.  In other words, if FILE_DELETED_REGEX matches, it
+	 does not necessarily mean that we are dealing with an
+	 anonymous shared mapping.  However, there is no easy way to
+	 detect this currently, so this is the best approximation we
+	 have.
+
+	 As a result, GDB will dump readonly pages of deleted
+	 executables when using the default value of coredump_filter
+	 (0x33), while the Linux kernel will not dump those pages.
+	 But we can live with that.  */
+      compile_rx_or_error (&file_deleted_regex, " (deleted)$",
+			   _("Could not compile regex to match "
+			     "'<file> (deleted)'"));
+      /* We will never release these regexes, so just discard the
+	 cleanups.  */
+      discard_cleanups (c);
+
+      /* If we reached this point, then everything succeeded.  */
+      init_regex_p = 1;
+    }
+
+  if (init_regex_p == -1)
+    {
+      const char deleted[] = " (deleted)";
+      size_t del_len = sizeof (deleted) - 1;
+      size_t filename_len = strlen (filename);
+
+      /* There was an error while compiling the regex'es above.  In
+	 order to try to give some reliable information to the caller,
+	 we just try to find the string " (deleted)" in the filename.
+	 If we managed to find it, then we assume the mapping is
+	 anonymous.  */
+      return (filename_len >= del_len
+	      && strcmp (filename + filename_len - del_len, deleted) == 0);
+    }
+
+  if (*filename == '\0'
+      || regexec (&dev_zero_regex, filename, 0, NULL, 0) == 0
+      || regexec (&shmem_file_regex, filename, 0, NULL, 0) == 0
+      || regexec (&file_deleted_regex, filename, 0, NULL, 0) == 0)
+    return 1;
+
+  return 0;
+}
+
+/* Return 0 if the memory mapping (which is related to FILTERFLAGS, V,
+   MAYBE_PRIVATE_P, and MAPPING_ANONYMOUS_P) should not be dumped, or
+   greater than 0 if it should.
+
+   In a nutshell, this is the logic that we follow in order to decide
+   if a mapping should be dumped or not.
+
+   - If the mapping is associated to a file whose name ends with
+     " (deleted)", or if the file is "/dev/zero", or if it is
+     "/SYSV%08x" (shared memory), or if there is no file associated
+     with it, or if the AnonHugePages: or the Anonymous: fields in the
+     /proc/PID/smaps have contents, then GDB considers this mapping to
+     be anonymous.  Otherwise, GDB considers this mapping to be a
+     file-backed mapping (because there will be a file associated with
+     it).
+ 
+     It is worth mentioning that, from all those checks described
+     above, the most fragile is the one to see if the file name ends
+     with " (deleted)".  This does not necessarily mean that the
+     mapping is anonymous, because the deleted file associated with
+     the mapping may have been a hard link to another file, for
+     example.  The Linux kernel checks to see if "i_nlink == 0", but
+     GDB cannot easily (and normally) do this check (iff running as
+     root, it could find the mapping in /proc/PID/map_files/ and
+     determine whether there still are other hard links to the
+     inode/file).  Therefore, we made a compromise here, and we assume
+     that if the file name ends with " (deleted)", then the mapping is
+     indeed anonymous.  FWIW, this is something the Linux kernel could
+     do better: expose this information in a more direct way.
+ 
+   - If we see the flag "sh" in the "VmFlags:" field (in
+     /proc/PID/smaps), then certainly the memory mapping is shared
+     (VM_SHARED).  If we have access to the VmFlags, and we don't see
+     the "sh" there, then certainly the mapping is private.  However,
+     Linux kernels before commit
+     834f82e2aa9a8ede94b17b656329f850c1471514 (3.10) do not have the
+     "VmFlags:" field; in that case, we use another heuristic: if we
+     see 'p' in the permission flags, then we assume that the mapping
+     is private, even though the presence of the 's' flag there would
+     mean VM_MAYSHARE, which means the mapping could still be private.
+     This should work OK enough, however.  */
+
+static int
+dump_mapping_p (unsigned int filterflags, const struct smaps_vmflags *v,
+		int maybe_private_p, int mapping_anon_p, int mapping_file_p,
+		const char *filename)
+{
+  /* Initially, we trust in what we received from our caller.  This
+     value may not be very precise (i.e., it was probably gathered
+     from the permission line in the /proc/PID/smaps list, which
+     actually refers to VM_MAYSHARE, and not VM_SHARED), but it is
+     what we have until we take a look at the "VmFlags:" field
+     (assuming that the version of the Linux kernel being used
+     supports it, of course).  */
+  int private_p = maybe_private_p;
+
+  /* We always dump vDSO and vsyscall mappings, because it's likely that
+     there'll be no file to read the contents from at core load time.
+     The kernel does the same.  */
+  if (strcmp ("[vdso]", filename) == 0
+      || strcmp ("[vsyscall]", filename) == 0)
+    return 1;
+
+  if (v->initialized_p)
+    {
+      /* We never dump I/O mappings.  */
+      if (v->io_page)
+	return 0;
+
+      /* Check if we should exclude this mapping.  */
+      if (v->exclude_coredump)
+	return 0;
+
+      /* Update our notion of whether this mapping is shared or
+	 private based on a trustworthy value.  */
+      private_p = !v->shared_mapping;
+
+      /* HugeTLB checking.  */
+      if (v->uses_huge_tlb)
+	{
+	  if ((private_p && (filterflags & COREFILTER_HUGETLB_PRIVATE))
+	      || (!private_p && (filterflags & COREFILTER_HUGETLB_SHARED)))
+	    return 1;
+
+	  return 0;
+	}
+    }
+
+  if (private_p)
+    {
+      if (mapping_anon_p && mapping_file_p)
+	{
+	  /* This is a special situation.  It can happen when we see a
+	     mapping that is file-backed, but that contains anonymous
+	     pages.  */
+	  return ((filterflags & COREFILTER_ANON_PRIVATE) != 0
+		  || (filterflags & COREFILTER_MAPPED_PRIVATE) != 0);
+	}
+      else if (mapping_anon_p)
+	return (filterflags & COREFILTER_ANON_PRIVATE) != 0;
+      else
+	return (filterflags & COREFILTER_MAPPED_PRIVATE) != 0;
+    }
+  else
+    {
+      if (mapping_anon_p && mapping_file_p)
+	{
+	  /* This is a special situation.  It can happen when we see a
+	     mapping that is file-backed, but that contains anonymous
+	     pages.  */
+	  return ((filterflags & COREFILTER_ANON_SHARED) != 0
+		  || (filterflags & COREFILTER_MAPPED_SHARED) != 0);
+	}
+      else if (mapping_anon_p)
+	return (filterflags & COREFILTER_ANON_SHARED) != 0;
+      else
+	return (filterflags & COREFILTER_MAPPED_SHARED) != 0;
+    }
+}
+
 /* Implement the "info proc" command.  */
 
 static void
@@ -819,48 +1113,97 @@ linux_find_memory_regions_full (struct gdbarch *gdbarch,
 				void *obfd)
 {
   char mapsfilename[100];
-  char *data;
+  char coredumpfilter_name[100];
+  char *data, *coredumpfilterdata;
+  pid_t pid;
+  /* Default dump behavior of coredump_filter (0x33), according to
+     Documentation/filesystems/proc.txt from the Linux kernel
+     tree.  */
+  unsigned int filterflags = (COREFILTER_ANON_PRIVATE
+			      | COREFILTER_ANON_SHARED
+			      | COREFILTER_ELF_HEADERS
+			      | COREFILTER_HUGETLB_PRIVATE);
 
   /* We need to know the real target PID to access /proc.  */
   if (current_inferior ()->fake_pid_p)
     return 1;
 
-  xsnprintf (mapsfilename, sizeof mapsfilename,
-	     "/proc/%d/smaps", current_inferior ()->pid);
+  pid = current_inferior ()->pid;
+
+  if (use_coredump_filter)
+    {
+      xsnprintf (coredumpfilter_name, sizeof (coredumpfilter_name),
+		 "/proc/%d/coredump_filter", pid);
+      coredumpfilterdata = target_fileio_read_stralloc (coredumpfilter_name);
+      if (coredumpfilterdata != NULL)
+	{
+	  sscanf (coredumpfilterdata, "%x", &filterflags);
+	  xfree (coredumpfilterdata);
+	}
+    }
+
+  xsnprintf (mapsfilename, sizeof mapsfilename, "/proc/%d/smaps", pid);
   data = target_fileio_read_stralloc (mapsfilename);
   if (data == NULL)
     {
       /* Older Linux kernels did not support /proc/PID/smaps.  */
-      xsnprintf (mapsfilename, sizeof mapsfilename,
-		 "/proc/%d/maps", current_inferior ()->pid);
+      xsnprintf (mapsfilename, sizeof mapsfilename, "/proc/%d/maps", pid);
       data = target_fileio_read_stralloc (mapsfilename);
     }
-  if (data)
+
+  if (data != NULL)
     {
       struct cleanup *cleanup = make_cleanup (xfree, data);
-      char *line;
+      char *line, *t;
 
-      line = strtok (data, "\n");
-      while (line)
+      line = strtok_r (data, "\n", &t);
+      while (line != NULL)
 	{
 	  ULONGEST addr, endaddr, offset, inode;
 	  const char *permissions, *device, *filename;
+	  struct smaps_vmflags v;
 	  size_t permissions_len, device_len;
-	  int read, write, exec;
-	  int modified = 0, has_anonymous = 0;
+	  int read, write, exec, private;
+	  int has_anonymous = 0;
+	  int should_dump_p = 0;
+	  int mapping_anon_p;
+	  int mapping_file_p;
 
+	  memset (&v, 0, sizeof (v));
 	  read_mapping (line, &addr, &endaddr, &permissions, &permissions_len,
 			&offset, &device, &device_len, &inode, &filename);
+	  mapping_anon_p = mapping_is_anonymous_p (filename);
+	  /* If the mapping is not anonymous, then we can consider it
+	     to be file-backed.  These two states (anonymous or
+	     file-backed) seem to be exclusive, but they can actually
+	     coexist.  For example, if a file-backed mapping has
+	     "Anonymous:" pages (see more below), then the Linux
+	     kernel will dump this mapping when the user specified
+	     that she only wants anonymous mappings in the corefile
+	     (*even* when she explicitly disabled the dumping of
+	     file-backed mappings).  */
+	  mapping_file_p = !mapping_anon_p;
 
 	  /* Decode permissions.  */
 	  read = (memchr (permissions, 'r', permissions_len) != 0);
 	  write = (memchr (permissions, 'w', permissions_len) != 0);
 	  exec = (memchr (permissions, 'x', permissions_len) != 0);
-
-	  /* Try to detect if region was modified by parsing smaps counters.  */
-	  for (line = strtok (NULL, "\n");
-	       line && line[0] >= 'A' && line[0] <= 'Z';
-	       line = strtok (NULL, "\n"))
+	  /* 'private' here actually means VM_MAYSHARE, and not
+	     VM_SHARED.  In order to know if a mapping is really
+	     private or not, we must check the flag "sh" in the
+	     VmFlags field.  This is done by decode_vmflags.  However,
+	     if we are using a Linux kernel released before the commit
+	     834f82e2aa9a8ede94b17b656329f850c1471514 (3.10), we will
+	     not have the VmFlags there.  In this case, there is
+	     really no way to know if we are dealing with VM_SHARED,
+	     so we just assume that VM_MAYSHARE is enough.  */
+	  private = memchr (permissions, 'p', permissions_len) != 0;
+
+	  /* Try to detect if region should be dumped by parsing smaps
+	     counters.  */
+	  for (line = strtok_r (NULL, "\n", &t);
+	       line != NULL && line[0] >= 'A' && line[0] <= 'Z';
+	       line = strtok_r (NULL, "\n", &t))
 	    {
 	      char keyword[64 + 1];
 
@@ -869,11 +1212,17 @@ linux_find_memory_regions_full (struct gdbarch *gdbarch,
 		  warning (_("Error parsing {s,}maps file '%s'"), mapsfilename);
 		  break;
 		}
+
 	      if (strcmp (keyword, "Anonymous:") == 0)
-		has_anonymous = 1;
-	      if (strcmp (keyword, "Shared_Dirty:") == 0
-		  || strcmp (keyword, "Private_Dirty:") == 0
-		  || strcmp (keyword, "Swap:") == 0
+		{
+		  /* Older Linux kernels did not support the
+		     "Anonymous:" counter.  Check it here.  */
+		  has_anonymous = 1;
+		}
+	      else if (strcmp (keyword, "VmFlags:") == 0)
+		decode_vmflags (line, &v);
+
+	      if (strcmp (keyword, "AnonHugePages:") == 0
 		  || strcmp (keyword, "Anonymous:") == 0)
 		{
 		  unsigned long number;
@@ -884,19 +1233,46 @@ linux_find_memory_regions_full (struct gdbarch *gdbarch,
 			       mapsfilename);
 		      break;
 		    }
-		  if (number != 0)
-		    modified = 1;
+		  if (number > 0)
+		    {
+		      /* Even if we are dealing with a file-backed
+			 mapping, if it contains anonymous pages we
+			 consider it to be *also* an anonymous
+			 mapping, because this is what the Linux
+			 kernel does:
+
+			 // Dump segments that have been written to.
+			 if (vma->anon_vma && FILTER(ANON_PRIVATE))
+			 	goto whole;
+
+			 Note that if the mapping is already marked as
+			 file-backed (i.e., mapping_file_p is
+			 non-zero), then this is a special case, and
+			 this mapping will be dumped either when the
+			 user wants to dump file-backed *or* anonymous
+			 mappings.  */
+		      mapping_anon_p = 1;
+		    }
 		}
 	    }
 
-	  /* Older Linux kernels did not support the "Anonymous:" counter.
-	     If it is missing, we can't be sure - dump all the pages.  */
-	  if (!has_anonymous)
-	    modified = 1;
+	  if (has_anonymous)
+	    should_dump_p = dump_mapping_p (filterflags, &v, private,
+					    mapping_anon_p, mapping_file_p,
+					    filename);
+	  else
+	    {
+	      /* Older Linux kernels did not support the "Anonymous:" counter.
+		 If it is missing, we can't be sure - dump all the pages.  */
+	      should_dump_p = 1;
+	    }
 
 	  /* Invoke the callback function to create the corefile segment.  */
-	  func (addr, endaddr - addr, offset, inode,
-		read, write, exec, modified, filename, obfd);
+	  if (should_dump_p)
+	    func (addr, endaddr - addr, offset, inode,
+		  read, write, exec, 1, /* MODIFIED is true because we
+					   want to dump the mapping.  */
+		  filename, obfd);
 	}
 
       do_cleanups (cleanup);
@@ -1972,6 +2348,17 @@ linux_infcall_mmap (CORE_ADDR size, unsigned prot)
   return retval;
 }
 
+/* Display whether the gcore command is using the
+   /proc/PID/coredump_filter file.  */
+
+static void
+show_use_coredump_filter (struct ui_file *file, int from_tty,
+			  struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Use of /proc/PID/coredump_filter file to generate"
+			    " corefiles is %s.\n"), value);
+}
+
 /* To be called from the various GDB_OSABI_LINUX handlers for the
    various GNU/Linux architectures and machine types.  */
 
@@ -2008,4 +2395,16 @@ _initialize_linux_tdep (void)
   /* Observers used to invalidate the cache when needed.  */
   observer_attach_inferior_exit (invalidate_linux_cache_inf);
   observer_attach_inferior_appeared (invalidate_linux_cache_inf);
+
+  add_setshow_boolean_cmd ("use-coredump-filter", class_files,
+			   &use_coredump_filter, _("\
+Set whether gcore should consider /proc/PID/coredump_filter."),
+			   _("\
+Show whether gcore should consider /proc/PID/coredump_filter."),
+			   _("\
+Use this command to set whether gcore should consider the contents\n\
+of /proc/PID/coredump_filter when generating the corefile.  For more information\n\
+about this file, refer to the manpage of core(5)."),
+			   NULL, show_use_coredump_filter,
+			   &setlist, &showlist);
 }