Re: [patch] Fix gcore writer for -Wl,-z,relro (PR corefiles/11804)

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

a slight warning() improvement.

There was a hint
	http://sourceware.org/bugzilla/show_bug.cgi?id=11804#c12
it may not always work right but that would be just a Linux kernel bug so that
GDB part should be OK.  Also it cannot be a regression, only more pages may be
written out with this patch.


Thanks,
Jan


On Tue, 31 Aug 2010 19:28:57 +0200, Jan Kratochvil wrote:
> technical rediff due to the patch update:
> 
> On Mon, 30 Aug 2010 11:15:21 +0200, Jan Kratochvil wrote:
> Hi,
> 
> currently for -Wl,-z,relro executables GDB will not dump the DYNAMIC segment
> into the core file, failing to read shared library list later.
> 
> (gdb) info sharedlibrary 
> >From                To                  Syms Read   Shared Object Library
> 0x00007ffff7dddb20  0x00007ffff7df5c74  Yes         /lib64/ld-linux-x86-64.so.2
> 
> This is just the fallback, GDB considers the executable uninitialized with
> DT_DEBUG value zero.
> 
> Linux kernel dumps it correctly, respecting if the page got ever modified
> since being read from the disk, even if it is not (no longer) writable.
> 
> No regressions on {x86_64,x86_64-m32,i686}-fedora14snapshot-linux-gnu.
> 
> The "Shared_Dirty:" / "Private_Dirty:" / "Swap:" rule has been suggested by
> Roland McGrath and confirmed by Larry Woodman.


gdb/
2010-09-22  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix gcore writer for -Wl,-z,relro.
	* defs.h (find_memory_region_ftype): New parameter `modified'.  New
	comment.
	* fbsd-nat.c (fbsd_find_memory_regions): Pass -1 to func.
	* gcore.c (gcore_create_callback): New parameter `modified'.
	Consider segment as unmodified only if also MODIFIED is 0.  Set
	SEC_READONLY just according to WRITE.
	(objfile_find_memory_regions): Pass new values for the `modified'
	parameter.
	* gnu-nat.c (gnu_find_memory_regions): Pass -1 for the
	`modified' parameter.
	* linux-nat.c (read_mapping): New parameters mapfilename and modified.
	(linux_nat_find_memory_regions): New variable `modified'.  Try
	"/proc/%d/smaps" first.  Pass `&modified' and `mapsfilename' to
	read_mapping.  Call func with MODIFIED.
	(linux_nat_info_proc_cmd): Pass `fname1' and NULL to read_mapping.
	* procfs.c (find_memory_regions_callback): Pass -1 for the `modified'
	parameter.

gdb/testsuite/
2010-09-22  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix gcore writer for -Wl,-z,relro.
	* gdb.base/gcore-relro.exp: New file.
	* gdb.base/gcore-relro-main.c: New file.
	* gdb.base/gcore-relro-lib.c: New file.

--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -638,9 +638,10 @@ extern void init_source_path (void);
 
 /* From exec.c */
 
+/* MODIFIED has value -1 for unknown, 0 for not modified, 1 for modified.  */
 typedef int (*find_memory_region_ftype) (CORE_ADDR addr, unsigned long size,
 					 int read, int write, int exec,
-					 void *data);
+					 int modified, void *data);
 
 /* Take over the 'find_mapped_memory' vector from exec.c. */
 extern void exec_set_find_memory_regions
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -133,7 +133,7 @@ fbsd_find_memory_regions (find_memory_region_ftype func, void *obfd)
 	}
 
       /* Invoke the callback function to create the corefile segment. */
-      func (start, size, read, write, exec, obfd);
+      func (start, size, read, write, exec, -1, obfd);
     }
 
   do_cleanups (cleanup);
--- a/gdb/gcore.c
+++ b/gdb/gcore.c
@@ -378,8 +378,8 @@ make_output_phdrs (bfd *obfd, asection *osec, void *ignored)
 }
 
 static int
-gcore_create_callback (CORE_ADDR vaddr, unsigned long size,
-		       int read, int write, int exec, void *data)
+gcore_create_callback (CORE_ADDR vaddr, unsigned long size, int read,
+		       int write, int exec, int modified, void *data)
 {
   bfd *obfd = data;
   asection *osec;
@@ -388,7 +388,7 @@ gcore_create_callback (CORE_ADDR vaddr, unsigned long size,
   /* If the memory segment has no permissions set, ignore it, otherwise
      when we later try to access it for read/write, we'll get an error
      or jam the kernel.  */
-  if (read == 0 && write == 0 && exec == 0)
+  if (read == 0 && write == 0 && exec == 0 && modified == 0)
     {
       if (info_verbose)
         {
@@ -399,7 +399,7 @@ gcore_create_callback (CORE_ADDR vaddr, unsigned long size,
       return 0;
     }
 
-  if (write == 0 && !solib_keep_data_in_core (vaddr, size))
+  if (write == 0 && modified == 0 && !solib_keep_data_in_core (vaddr, size))
     {
       /* See if this region of memory lies inside a known file on disk.
 	 If so, we can avoid copying its contents by clearing SEC_LOAD.  */
@@ -431,10 +431,12 @@ gcore_create_callback (CORE_ADDR vaddr, unsigned long size,
 	    }
 	}
 
-    keep:
-      flags |= SEC_READONLY;
+    keep:;
     }
 
+  if (write == 0)
+    flags |= SEC_READONLY;
+
   if (exec)
     flags |= SEC_CODE;
   else
@@ -484,6 +486,7 @@ objfile_find_memory_regions (find_memory_region_ftype func, void *obfd)
 			 1, /* All sections will be readable.  */
 			 (flags & SEC_READONLY) == 0, /* Writable.  */
 			 (flags & SEC_CODE) != 0, /* Executable.  */
+			 -1, /* Modified is unknown.  */
 			 obfd);
 	  if (ret != 0)
 	    return ret;
@@ -496,6 +499,7 @@ objfile_find_memory_regions (find_memory_region_ftype func, void *obfd)
 	     1, /* Stack section will be readable.  */
 	     1, /* Stack section will be writable.  */
 	     0, /* Stack section will not be executable.  */
+	     1, /* Stack section will be modified.  */
 	     obfd);
 
   /* Make a heap segment. */
@@ -504,6 +508,7 @@ objfile_find_memory_regions (find_memory_region_ftype func, void *obfd)
 	     1, /* Heap section will be readable.  */
 	     1, /* Heap section will be writable.  */
 	     0, /* Heap section will not be executable.  */
+	     1, /* Heap section will be modified.  */
 	     obfd);
 
   return 0;
--- a/gdb/gnu-nat.c
+++ b/gdb/gnu-nat.c
@@ -2544,7 +2544,7 @@ gnu_find_memory_regions (find_memory_region_ftype func, void *data)
 		     last_protection & VM_PROT_READ,
 		     last_protection & VM_PROT_WRITE,
 		     last_protection & VM_PROT_EXECUTE,
-		     data);
+		     -1, data);
 	  last_region_address = region_address;
 	  last_region_end = region_address += region_length;
 	  last_protection = protection;
@@ -2557,7 +2557,7 @@ gnu_find_memory_regions (find_memory_region_ftype func, void *data)
 	     last_protection & VM_PROT_READ,
 	     last_protection & VM_PROT_WRITE,
 	     last_protection & VM_PROT_EXECUTE,
-	     data);
+	     -1, data);
 
   return 0;
 }
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -4078,12 +4078,9 @@ linux_child_pid_to_exec_file (int pid)
 /* Service function for corefiles and info proc.  */
 
 static int
-read_mapping (FILE *mapfile,
-	      long long *addr,
-	      long long *endaddr,
-	      char *permissions,
-	      long long *offset,
-	      char *device, long long *inode, char *filename)
+read_mapping (FILE *mapfile, const char *mapfilename, long long *addr,
+	      long long *endaddr, char *permissions, long long *offset,
+	      char *device, long long *inode, char *filename, int *modified)
 {
   int ret = fscanf (mapfile, "%llx-%llx %s %llx %s %llx",
 		    addr, endaddr, permissions, offset, device, inode);
@@ -4101,6 +4098,41 @@ read_mapping (FILE *mapfile,
       ret += fscanf (mapfile, "%[^\n]\n", filename);
     }
 
+  if (modified != NULL)
+    {
+      *modified = -1;
+      for (;;)
+	{
+	  int ch, got;
+	  char keyword[64 + 1];
+	  unsigned long number;
+
+	  ch = fgetc (mapfile);
+	  if (ch != EOF)
+	    ungetc (ch, mapfile);
+	  if (ch < 'A' || ch > 'Z')
+	    break;
+	  got = fscanf (mapfile, "%64s%lu", keyword, &number);
+	  do
+	    ch = fgetc (mapfile);
+	  while (ch != EOF && ch != '\n');
+	  if (got != 2)
+	    {
+	      warning (_("Error parsing file %s"), mapfilename);
+	      break;
+	    }
+	  if (number != 0 && (strcmp (keyword, "Shared_Dirty:") == 0
+			      || strcmp (keyword, "Private_Dirty:") == 0
+			      || strcmp (keyword, "Swap:") == 0))
+	    *modified = 1;
+	  else if (*modified == -1)
+	    {
+	      /* A valid line proves an smaps file is being read in.  */
+	      *modified = 0;
+	    }
+	}
+    }
+
   return (ret != 0 && ret != EOF);
 }
 
@@ -4115,13 +4147,17 @@ linux_nat_find_memory_regions (find_memory_region_ftype func, void *obfd)
   FILE *mapsfile;
   long long addr, endaddr, size, offset, inode;
   char permissions[8], device[8], filename[MAXPATHLEN];
-  int read, write, exec;
+  int read, write, exec, modified;
   struct cleanup *cleanup;
 
   /* Compose the filename for the /proc memory map, and open it.  */
-  sprintf (mapsfilename, "/proc/%d/maps", pid);
+  sprintf (mapsfilename, "/proc/%d/smaps", pid);
   if ((mapsfile = fopen (mapsfilename, "r")) == NULL)
-    error (_("Could not open %s."), mapsfilename);
+    {
+      sprintf (mapsfilename, "/proc/%d/maps", pid);
+      if ((mapsfile = fopen (mapsfilename, "r")) == NULL)
+	error (_("Could not open %s."), mapsfilename);
+    }
   cleanup = make_cleanup_fclose (mapsfile);
 
   if (info_verbose)
@@ -4129,8 +4165,9 @@ linux_nat_find_memory_regions (find_memory_region_ftype func, void *obfd)
 		      "Reading memory regions from %s\n", mapsfilename);
 
   /* Now iterate until end-of-file.  */
-  while (read_mapping (mapsfile, &addr, &endaddr, &permissions[0],
-		       &offset, &device[0], &inode, &filename[0]))
+  while (read_mapping (mapsfile, mapsfilename, &addr, &endaddr,
+		       &permissions[0], &offset, &device[0], &inode,
+		       &filename[0], &modified))
     {
       size = endaddr - addr;
 
@@ -4153,7 +4190,7 @@ linux_nat_find_memory_regions (find_memory_region_ftype func, void *obfd)
 
       /* Invoke the callback function to create the corefile
 	 segment.  */
-      func (addr, size, read, write, exec, obfd);
+      func (addr, size, read, write, exec, modified, obfd);
     }
   do_cleanups (cleanup);
   return 0;
@@ -4615,8 +4652,9 @@ linux_nat_info_proc_cmd (char *args, int from_tty)
 			   "      Size", "    Offset", "objfile");
 	    }
 
-	  while (read_mapping (procfile, &addr, &endaddr, &permissions[0],
-			       &offset, &device[0], &inode, &filename[0]))
+	  while (read_mapping (procfile, fname1, &addr, &endaddr,
+			       &permissions[0], &offset, &device[0], &inode,
+			       &filename[0], NULL))
 	    {
 	      size = endaddr - addr;
 
--- a/gdb/procfs.c
+++ b/gdb/procfs.c
@@ -5285,7 +5285,7 @@ find_memory_regions_callback (struct prmap *map,
 		  (map->pr_mflags & MA_READ) != 0,
 		  (map->pr_mflags & MA_WRITE) != 0,
 		  (map->pr_mflags & MA_EXEC) != 0,
-		  data);
+		  -1, data);
 }
 
 /* External interface.  Calls a callback function once for each
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gcore-relro-lib.c
@@ -0,0 +1,21 @@
+/* Copyright 2010 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/>.  */
+
+void
+lib (void)
+{
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gcore-relro-main.c
@@ -0,0 +1,25 @@
+/* Copyright 2010 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/>.  */
+
+extern void lib (void);
+
+int
+main (void)
+{
+  lib ();
+  return 0;
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gcore-relro.exp
@@ -0,0 +1,80 @@
+# Copyright 2010 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/>.
+
+if {[skip_shlib_tests]} {
+    return 0
+}
+
+set testfile "gcore-relro"
+set srcmainfile ${testfile}-main.c
+set srclibfile ${testfile}-lib.c
+set libfile ${objdir}/${subdir}/${testfile}-lib.so
+set objfile ${objdir}/${subdir}/${testfile}-main.o
+set executable ${testfile}-main
+set binfile ${objdir}/${subdir}/${executable}
+set gcorefile ${objdir}/${subdir}/${executable}.gcore
+
+if { [gdb_compile_shlib ${srcdir}/${subdir}/${srclibfile} ${libfile} {debug}] != ""
+     || [gdb_compile ${srcdir}/${subdir}/${srcmainfile} ${objfile} object {debug}] != "" } {
+     untested ${testfile}.exp
+     return -1
+}
+set opts [list debug shlib=${libfile} additional_flags=-Wl,-z,relro]
+if { [gdb_compile ${objfile} ${binfile} executable $opts] != "" } {
+     unsupported "-Wl,-z,relro compilation failed"
+     return -1
+}
+
+clean_restart $executable
+gdb_load_shlibs $libfile
+
+# Does this gdb support gcore?
+set test "help gcore"
+gdb_test_multiple $test $test {
+    -re "Undefined command: .gcore.*\r\n$gdb_prompt $" {
+	# gcore command not supported -- nothing to test here.
+	unsupported "gdb does not support gcore on this target"
+	return -1;
+    }
+    -re "Save a core file .*\r\n$gdb_prompt $" {
+	pass $test
+    }
+}
+
+if { ![runto lib] } then {
+    return -1
+}
+
+set escapedfilename [string_to_regexp ${gcorefile}]
+
+set test "save a corefile"
+gdb_test_multiple "gcore ${gcorefile}" $test {
+    -re "Saved corefile ${escapedfilename}\r\n$gdb_prompt $" {
+	pass $test
+    }
+    -re "Can't create a corefile\r\n$gdb_prompt $" {
+	unsupported $test
+	return -1
+    }
+}
+
+# Now restart gdb and load the corefile.
+
+clean_restart $executable
+gdb_load_shlibs $libfile
+
+gdb_test "core ${gcorefile}" "Core was generated by .*" "re-load generated corefile"
+
+gdb_test "frame" "#0 \[^\r\n\]* lib .*" "library got loaded"