1 files changed, 66 insertions, 0 deletions
diff --git a/xpcom/reflect/xptcall/md/unix/vtable_layout_x86.cpp b/xpcom/reflect/xptcall/md/unix/vtable_layout_x86.cpp
new file mode 100644
index 0000000000..9139d4b2aa
--- /dev/null
+++ b/xpcom/reflect/xptcall/md/unix/vtable_layout_x86.cpp
@@ -0,0 +1,66 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* this code contributed by Bert Driehuis <bert_driehuis@nl.compuware.com> */
+
+#include <stdio.h>
+
+// Try to determine the vtable layout generated by G++
+// Produces the offset at which the first vtable entry can be
+// found, and the factor to apply for subsequent entries on stdout.
+// Example output:
+//    #define GCC_VTABLE_START        0xc
+//    #define GCC_VTABLE_FACTOR       0x8
+
+class test {
+public:
+      virtual int     t1(void);
+      virtual int     t2(void);
+      int             x;
+};
+
+test::test() { this->x = 0x12121212; };
+
+int test::t1(void) { return 1; }
+int test::t2(void) { return 2; }
+
+void die(char *x) {
+      fprintf(stderr, "%s\n", x);
+      exit(1);
+}
+
+int
+main()
+{
+      int             i;
+      test           *t = new test();
+      int            *tp = (int *) t;
+      int             off1 = -1;
+      int             off2 = -1;
+      int             factor;
+      int             factorshift;
+
+      if (*tp++ != 0x12121212)
+              die("Integer element test::x not found!");
+      tp = (int *) *tp;
+      for (i = 0; i < 10; i++) {
+              if (tp[i] == (int) t->t1)
+                      off1 = i;
+              if (tp[i] == (int) t->t2)
+                      off2 = i;
+      }
+      if (off1 == -1 || off2 == -1)
+              die("Could not determine offset into vtable!");
+      factor = (off2 - off1) * 4;
+      factorshift = -1;
+      while (factor) {
+              factorshift++;
+              factor >>= 1;
+      }
+      printf("/* Automatically generated by vtable_layout_x86.cpp */\n");
+      printf("#define GCC_VTABLE_START\t0x%x\n", off1 * 4);
+      printf("#define GCC_VTABLE_FACTOR\t0x%x\n", (off2 - off1) * 4);
+      printf("#define GCC_VTABLE_SHIFT\t0x%x\n", factorshift);
+      exit(0);
+}