Next: Statics, Previous: Register Variables, Up: Variables

### 4.4 Common Blocks

A common block is a statically allocated section of memory which can be referred to by several source files. It may contain several variables. I believe Fortran is the only language with this feature.

A `N_BCOMM` stab begins a common block and an `N_ECOMM` stab ends it. The only field that is significant in these two stabs is the string, which names a normal (non-debugging) symbol that gives the address of the common block. According to IBM documentation, only the `N_BCOMM` has the name of the common block (even though their compiler actually puts it both places).

The stabs for the members of the common block are between the `N_BCOMM` and the `N_ECOMM`; the value of each stab is the offset within the common block of that variable. IBM uses the `C_ECOML` stab type, and there is a corresponding `N_ECOML` stab type, but Sun's Fortran compiler uses `N_GSYM` instead. The variables within a common block use the ‘`V`’ symbol descriptor (I believe this is true of all Fortran variables). Other stabs (at least type declarations using `C_DECL`) can also be between the `N_BCOMM` and the `N_ECOMM`.