The Tor Browser: xpcom/reflect/xptcall/src/md/unix/vtable_layout

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

     1 /* This Source Code Form is subject to the terms of the Mozilla Public

     2  * License, v. 2.0. If a copy of the MPL was not distributed with this

     3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     5 /* this code contributed by Bert Driehuis <bert_driehuis@nl.compuware.com> */

     7 #include <stdio.h>

     9 // Try to determine the vtable layout generated by G++

    10 // Produces the offset at which the first vtable entry can be

    11 // found, and the factor to apply for subsequent entries on stdout.

    12 // Example output:

    13 //    #define GCC_VTABLE_START        0xc

    14 //    #define GCC_VTABLE_FACTOR       0x8

    16 class test {

    17 public:

    18       virtual int     t1(void);

    19       virtual int     t2(void);

    20       int             x;

    21 };

    23 test::test() { this->x = 0x12121212; };

    25 int test::t1(void) { return 1; }

    26 int test::t2(void) { return 2; }

    28 void die(char *x) {

    29       fprintf(stderr, "%s\n", x);

    30       exit(1);

    31 }

    33 int

    34 main()

    35 {

    36       int             i;

    37       test           *t = new test();

    38       int            *tp = (int *) t;

    39       int             off1 = -1;

    40       int             off2 = -1;

    41       int             factor;

    42       int             factorshift;

    44       if (*tp++ != 0x12121212)

    45               die("Integer element test::x not found!");

    46       tp = (int *) *tp;

    47       for (i = 0; i < 10; i++) {

    48               if (tp[i] == (int) t->t1)

    49                       off1 = i;

    50               if (tp[i] == (int) t->t2)

    51                       off2 = i;

    52       }

    53       if (off1 == -1 || off2 == -1)

    54               die("Could not determine offset into vtable!");

    55       factor = (off2 - off1) * 4;

    56       factorshift = -1;

    57       while (factor) {

    58               factorshift++;

    59               factor >>= 1;

    60       }

    61       printf("/* Automatically generated by vtable_layout_x86.cpp */\n");

    62       printf("#define GCC_VTABLE_START\t0x%x\n", off1 * 4);

    63       printf("#define GCC_VTABLE_FACTOR\t0x%x\n", (off2 - off1) * 4);

    64       printf("#define GCC_VTABLE_SHIFT\t0x%x\n", factorshift);

    65       exit(0);

    66 }

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