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POgcc with electric fence library does not take effect
 

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  1. POgcc with electric fence library does not take effect
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    <p>I have written a snippet that has memory problems when dynamically allocating; when compiled with <code>-lefence</code> option, it seems that there is no effect. Here is the code segment:</p> <pre><code>int main(int argc, char *argv[]) { int *a = (int *)malloc(2*sizeof(int)); for(int i = 0; i &lt;=2; ++i){ a[i] = i; printf ("%d\n",a[i]); } free(a); return 0; } </code></pre> <p>And the compilation options:</p> <pre><code>gcc -g3 -Wall -std=c99 outOfBound.c -lefence </code></pre> <p>The expected result is that when <code>a.out</code> is executed there would be a core dump after <code>i</code> is assigned to 2 and <code>a[i]=i</code> is invoked.</p> <p>So Why <code>-lefence</code> has no effect?</p> <p>I have also increased the upper bound in the loop to 9, but there is still no core dump that<code>electric-fence</code> invoked. (Actually there is indeed a core dump by default, but this might due to the <code>MALLOC_CHECK_</code> env virable since when I <code>export MALLOC_CHECK_=0</code>, there would be no more core dump).</p> <p><strong>UPDATE</strong>: the whole result of <code>nm -A a.out</code> is as below:</p> <pre><code>a.out:08049f28 d _DYNAMIC a.out:08049ff4 d _GLOBAL_OFFSET_TABLE_ a.out:0804864c R _IO_stdin_used a.out: w _Jv_RegisterClasses a.out:08049f18 d __CTOR_END__ a.out:08049f14 d __CTOR_LIST__ a.out:08049f20 d __DTOR_END__ a.out:08049f1c d __DTOR_LIST__ a.out:08048718 r __FRAME_END__ a.out:08049f24 d __JCR_END__ a.out:08049f24 d __JCR_LIST__ a.out:0804a01c A __bss_start a.out:0804a014 D __data_start a.out:08048600 t __do_global_ctors_aux a.out:08048480 t __do_global_dtors_aux a.out:0804a018 d __dso_handle a.out: w __gmon_start__ a.out:080485f2 t __i686.get_pc_thunk.bx a.out:00000000 a __init_array_end a.out:00000000 a __init_array_start a.out:080485f0 T __libc_csu_fini a.out:08048580 T __libc_csu_init a.out: U __libc_start_main a.out:0804a01c A _edata a.out:0804a024 A _end a.out:0804862c T _fini a.out:08048648 R _fp_hw a.out:080483b4 T _init a.out:08048450 T _start a.out:0804a01c b completed.6159 a.out:0804a014 W data_start a.out:0804a020 b dtor_idx.6161 a.out:080484e0 t frame_dummy a.out: U free a.out:08048504 T main a.out: U malloc a.out: U printf </code></pre> <p>(I am using a debian package <code>electric-fence</code> on Ubuntu 12.04 32bit, <code>gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3</code>)</p> <h1>Update(20140801):</h1> <p>For <code>electric-fence</code> of version <code>2.2.4</code> packaged by debian(testing branch, i.e. jessie), it works. </p>
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    1. CONot sure if this helps, but for me it works as expected (i.e. generates a segfault). However, I used the source from [here](http://linux.softpedia.com/get/Programming/Debuggers/Electric-Fence-3305.shtml), built it using the Makefile, and also I had to add `-lpthread` to the linker options, otherwise it wouldn't link. Also, I am on Fedora.
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      1. USjogojapan
    2. CO@jogojapan Thanks. There is indeed a possibility that the deb is not packed well.
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      1. USHongxu Chen
 

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