gcc name bug?

[Frederic Tessier <ftessier@physics.uottawa.ca>]

-- System Information -------------------------------------------
Debian Release: stable on Pentium III
Kernel Version: Linux 2.2.18pre21/2.2.19
gcc version: 2.95.2
----------------------------------------------------------------- 

Hi,

While trying to optimize some C code for speed, we have
encountered what we think is a very strange bug with gcc: the
execution time depends on the name of the executable (!). As an
example, here is a bares bones C code snippet which reproduces
the problem:


/* strange.c ==================================================*/

#define N 1000000000

double content()
{
    return 0;
}

int main()
{
    int    i;
    double bucket=0;

    for (i=0; i<N; i++)
        bucket += content();

    return 0;
}

/*=============================================================*/


When we compile this program (gcc strange.c) and time its
execution (time a.out) we obtain:

       real    0m23.247s
       user    0m23.240s
       sys     0m0.000s

where "user" is the time we are interested in. Upon renaming the
executable we find two widely different execution times:

       trial    name of executable		user time (s)
       ---------------------------------------------------------
       1	a				23.24
       2	aa				23.25
       3	aaa				23.24
       4	aaaa				23.24
       5	aaaaa					49.92
       6	aaaaaa					49.91
       7	aaaaaaa					49.92
       8	aaaaaaaa				49.92
       9	aaaaaaaaa				49.91
       10	aaaaaaaaaa				49.90
       11	aaaaaaaaaaa				49.90
       12	aaaaaaaaaaaa				49.94
       13	aaaaaaaaaaaaa			23.24	
       14	aaaaaaaaaaaaaa			23.21
       15	aaaaaaaaaaaaaaa			23.39
       16	aaaaaaaaaaaaaaaa		23.62
       17	aaaaaaaaaaaaaaaaa		23.79
       18	aaaaaaaaaaaaaaaaaa		23.82
       19	aaaaaaaaaaaaaaaaaaa		23.57
       20	aaaaaaaaaaaaaaaaaaaa		22.83
       21	aaaaaaaaaaaaaaaaaaaaa			48.06
       22	aaaaaaaaaaaaaaaaaaaaaa			49.02
       23	aaaaaaaaaaaaaaaaaaaaaaa			49.93
       24	aaaaaaaaaaaaaaaaaaaaaaaa		49.91
       etc.
       ---------------------------------------------------------

We are not familiar with the intricate workings of the compiler,
but this must have to do with an alignment problem when the
executable is launched, as the changes typically occur when the
name length is increased by 8 bytes. This is a serious bug since
in our simple example it more than doubles the execution time
when we choose a "bad" name!

We have reproduced the problem on Pentium III machine with gcc
2.95, with a variety of kernels, and with C and C++ codes of
varying complexity. The "time" function is not the culprit, since
we can confirm our results with a wall clock.

We would like to know:

1) Does this behavior occur on other systems?

2) Is this a known issue?

3) Can the cause of the problem be identified?

4) Is there any workaround (e.g. compiler option)?

Thanks a bunch,
Fred.