[patch] watchpoint for babl

babl-malloc_f-watchpoint.patch (text/plain), 4.34 KB, created by Martin von Gagern on 2011-02-28 19:38:41 UTC

diff --git a/babl/babl-memory.c b/babl/babl-memory.c
index 6ceca90..154dd21 100644
--- a/babl/babl-memory.c
+++ b/babl/babl-memory.c
@@ -16,6 +16,8 @@
  * <http://www.gnu.org/licenses/>.
  */
 
+#define _GNU_SOURCE 1
+
 #include "config.h"
 #include <stdint.h>
 #include <stdlib.h>
@@ -23,6 +25,17 @@
 #include <string.h>
 #include "babl-internal.h"
 
+#include <sys/types.h>
+#include <unistd.h>
+#include <sys/ptrace.h>
+#include <linux/ptrace.h>
+#include <sys/user.h>
+#include <sys/debugreg.h>
+#include <assert.h>
+#include <unistd.h>
+#include <errno.h>
+#include <signal.h>
+
 static BablMallocFunc malloc_f = malloc;
 static BablFreeFunc   free_f   = free;
 
@@ -32,12 +45,24 @@ static void *first_free_used   = NULL;
 void
 babl_set_malloc (BablMallocFunc malloc_function)
 {
+  fprintf (stderr,
+           "babl_set_malloc:\n"
+           " first_malloc_used: %p\n"
+           " old malloc_f:      %p\n"
+           " malloc_function:   %p\n",
+           first_malloc_used, malloc_f, malloc_function);
   malloc_f = malloc_function;
 }
 
 void
 babl_set_free (BablFreeFunc free_function)
 {
+  fprintf (stderr,
+           "babl_set_free:\n"
+           " first_free_used:   %p\n"
+           " old free_f:        %p\n"
+           " free_function:     %p\n",
+           first_free_used, free_f, free_function);
   free_f = free_function;
 }
 
@@ -78,6 +103,68 @@ mem_stats (void)
 
 #endif
 
+static void set_watchpoint(void* addr) {
+  /* Thanks to jankratochvil in #gdb@freenode who pointed this out:
+     http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/tests/ptrace-tests/tests/watchpoint.c?cvsroot=systemtap
+  */
+
+  pid_t child;
+  int status;
+  unsigned long dr7;
+  long l;
+
+  child = fork ();
+  switch (child)
+    {
+    case -1:
+      assert (0);
+    case 0:
+      assert (ptrace (PTRACE_TRACEME, 0, NULL, NULL) == 0);
+      assert (raise (SIGTRAP) == 0);
+
+      return;
+    default:
+      break;
+    }
+
+  assert (waitpid (child, &status, 0) == child);
+  assert (WIFSTOPPED (status));
+  assert (WSTOPSIG (status) == SIGTRAP);
+
+  errno = 0;
+  l = ptrace (PTRACE_POKEUSER, child,
+	      offsetof (struct user, u_debugreg[0]), (unsigned long) addr);
+  assert_perror (errno);
+  assert (l == 0);
+
+  dr7 = (DR_RW_WRITE << DR_CONTROL_SHIFT);
+
+#ifdef DR_LEN_8
+  /*
+   * For a 32-bit build, DR_LEN_8 might be defined by the header.
+   * On a 64-bit kernel, we might even be able to use it.
+   * But we can't tell, and we don't really need it, so just use DR_LEN_4.
+   */
+  if (sizeof (long) > 4)
+    dr7 |= (DR_LEN_8 << DR_CONTROL_SHIFT);
+  else
+#endif
+    dr7 |= (DR_LEN_4 << DR_CONTROL_SHIFT);
+  dr7 |= (1UL << DR_LOCAL_ENABLE_SHIFT);
+  dr7 |= (1UL << DR_GLOBAL_ENABLE_SHIFT);
+
+  l = ptrace (PTRACE_POKEUSER, child, offsetof (struct user, u_debugreg[7]), dr7);
+  assert_perror (errno);
+  assert (l == 0);
+
+  errno = 0;
+  l = ptrace (PTRACE_CONT, child, 0l, 0l);
+  assert_perror (errno);
+  assert (l == 0);
+
+  exit(0);
+}
+
 static void
 functions_sanity (void)
 {
@@ -86,11 +173,36 @@ functions_sanity (void)
     {
       if (first_malloc_used == NULL)
         {
+          fprintf (stderr,
+                   "First use of malloc:\n"
+                   " first_malloc_used: %p\n"
+                   " malloc_f:          %p\n"
+                   " first_free_used:   %p\n"
+                   " free_f:            %p\n",
+                   first_malloc_used, malloc_f, first_free_used, free_f);
+          /*
+          fprintf (stderr, "Please attach debugger to pid %lu and press enter",
+                   (unsigned long)getpid());
+          {
+            char buf[30];
+            fgets(buf, sizeof(buf), stdin);
+          }
+          */
           first_malloc_used = malloc_f;
           first_free_used   = free_f;
+          fprintf (stderr, "Watching for writes to %p\n", &malloc_f);
+          set_watchpoint(&malloc_f);
         }
       else
         {
+          fprintf (stderr,
+                   "babl memory function(s) attempted switched on the fly:\n"
+                   " first_malloc_used: %p\n"
+                   " malloc_f:          %p\n"
+                   " first_free_used:   %p\n"
+                   " free_f:            %p\n",
+                   first_malloc_used, malloc_f, first_free_used, free_f);
+          abort ();
           babl_fatal ("babl memory function(s) attempted switched on the fly");
         }
     }