Andrew Pinski <pinskia at gcc dot> changed:

           What    |Removed                     |Added
             Status|UNCONFIRMED                 |RESOLVED
          Component|c                           |other
         Resolution|---                         |INVALID

--- Comment #2 from Andrew Pinski <pinskia at gcc dot> ---
You need -fno-common instead:

In C code, this option controls the placement of global variables defined
without an initializer, known as tentative definitions in the C standard.
Tentative definitions are distinct from declarations of a variable with the
extern keyword, which do not allocate storage.

Unix C compilers have traditionally allocated storage for uninitialized global
variables in a common block. This allows the linker to resolve all tentative
definitions of the same variable in different compilation units to the same
object, or to a non-tentative definition. This is the behavior specified by
-fcommon, and is the default for GCC on most targets. On the other hand, this
behavior is not required by ISO C, and on some targets may carry a speed or
code size penalty on variable references.

The -fno-common option specifies that the compiler should instead place
uninitialized global variables in the data section of the object file. This
inhibits the merging of tentative definitions by the linker so you get a
multiple-definition error if the same variable is defined in more than one
compilation unit. Compiling with -fno-common is useful on targets for which it
provides better performance, or if you wish to verify that the program will
work on other systems that always treat uninitialized variable definitions this

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