Hello,
I've run into this strange warning when compiling w/ optimization:
gcc-4.3 -O2 -Werror -Wall -c -o t.o t.c
cc1: warnings being treated as errors
t.c: In function ‘foo’:
t.c:25: error: array subscript is below array bounds
gcc-4.4 gives the same warning/error, however, gcc 4.1 and 4.2 compiles
the source.
gcc-4.1 -v says:
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++
--prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.1.3 --program-suffix=-4.1
--enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug
--with-tune=generic --enable-checking=release x86_64-linux-gnu
Thread model: posix
gcc version 4.1.3 20080704 (prerelease) (Debian 4.1.2-27)
gcc-4.2 -v says:
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-mpfr --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.2.4 (Debian 4.2.4-6)
gcc-4.3 -v says:
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.3.4-2'
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--enable-shared --enable-multiarch --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-mpfr --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.3.4 (Debian 4.3.4-2)
gcc-4.4 -v says:
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.1-1'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--enable-shared --enable-multiarch --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4
--program-suffix=-4.4 --enable-nls --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --enable-objc-gc
--with-arch-32=i486 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.1 (Debian 4.4.1-1)
t.c is :
---->8---->8---->8---->8---->8---->8---->8---->8---->8---->8----
#define ASSERT(x) if (x) { } else { __asm__("int $0x03"); }
#define SIZE 5
char hnd[SIZE];
char flg[SIZE];
char crd();
int idx(char);
void set(int i, char v);
#if 1
void set(int i, char v)
{
ASSERT(i >=0 && i < SIZE);
flg[i] = v;
}
#endif
void foo()
{
char c = crd();
int i = idx(0);
ASSERT(i != -1);
hnd[i] = c; // array subscript is below array bounds
set(i, 1);
}
---->8---->8---->8---->8---->8---->8---->8---->8---->8---->8----
Suppose that idx(c) returns the position of c in an array, an the return
value of -1 means that c is not in the array. The assertion checks that.
The funny thing is, if I change the source a bit, the warning goes away:
1) set '#if 1' to '#if 0' so that only the prototype of set() is visible
2) comment out the ASSERT() int set()
3) comment out ASSERT() just before the marked line
4) comment out set(i, 1) just after the marked line
The warning is not present under -O2.
Is this warning legal?
Cheers, Peter
