Initialize array in gcc, undefined reference to `memcpy'

Question

I'm coding C in Nachos3.4, Centos 6.0, compile by gcc 2.95.3,

the command line I use is gmake all

when I compile this, everything is fine

int main()
{
    char* fname[] = {"c(0)", "c(1)", "c(2)", "c(3)", "c(4)", "c(5)", "c(6)", "c(7)"};
    return 0;
}

but when I do this, it said undefined reference to 'memcpy'

int main()
{
    char* fname[] = {"c(0)", "c(1)", "c(2)", "c(3)", "c(4)", "c(5)", "c(6)", "c(7)", "c(8)"};
    return 0;
}

where is the problem and how can i fix that ?

Please show the (minimal) complete code to reproduce this, including the command line you're using to compile this. — Mat, May 07 '15 at 10:18
_gcc 2.95.3_ is quite outdated compiler, may be it has problems linking with libc shipped in _CentOS 6.0_ due to ABi incompability? — myaut, May 07 '15 at 10:32
I do try the latest gcc but it isn't compatible well with nachos3.4. — Fish, May 07 '15 at 10:36
Try checking if that ancient compiler has some form of the "no standard library" switch. — unwind, May 07 '15 at 10:38

score 2 · Accepted Answer · answered May 07 '15 at 19:52

Your initialisation of the automatic fname array involves the compiler constructing a copy of a large amount of data from a hidden static array to your array on the stack. GCC has several techniques it can use for this, one of it's favourites is to call the C library memcpy routine as this should be nice and quick whatever happens.

In your case you don't seem to have a C library so this is a problem.

You can tell GCC to always use the x86 instructions rather than calling the library like this:

gcc -mstringop-strategy=rep_byte -c -O file.c

or

gcc -mstringop-strategy=loop -c -O file.c

However, I was under the impression that GCC didn't start doing this till somewhere in the mid version 3.x.

Perhaps you're using a 'MIPS' processor, teachers like that processor, in which the required option would be -mno-memcpy.

Initialize array in gcc, undefined reference to `memcpy'

1 Answers1