>Submitter-Id: net
>Originator: Steven Young
>Organization: n/a
>Confidential: no
>Synopsis: gcc allows negatively-sized arrays
>Severity: non-critical
>Priority: low
>Category: c
>Class: accepts-illegal
>Release: gcc (GCC) 4.1.2 (Ubuntu 4.1.2-0ubuntu4)
>Environment:
System: Linux pc1 2.6.20-15-generic #2 SMP Sun Apr 15 07:36:31 UTC 2007 i686
GNU/Linux
Architecture: i686
host: i486-pc-linux-gnu
build: i486-pc-linux-gnu
target: i486-pc-linux-gnu
configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --enable-checking=release i486-linux-gnu
>Description:
By using an integer variable as the size of an array to be
initialized on the stack, you can trick gcc into accepting
and trying to create a negatively-sized array. The assembly
it generates in such a case seems to indicate it really thinks
it has a negatively-sized array.
>How-To-Repeat:
#include <stdio.h>
int main(int argc, char **argv) {
int x = -2;
int y[x];
printf("%d\n", sizeof(y));
}
This will output -8.
>Fix:
I don't know.
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