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(as.info)bss

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bss Section
===========

   The bss section is used for local common variable storage.  You may
allocate address space in the bss section, but you may not dictate data
to load into it before your program executes.  When your program starts
running, all the contents of the bss section are zeroed bytes.

   The `.lcomm' pseudo-op defines a symbol in the bss section; see
Note: `.lcomm'.

   The `.comm' pseudo-op may be used to declare a common symbol, which
is another form of uninitialized symbol; see Note: `.comm'.

   When assembling for a target which supports multiple sections, such
as ELF or COFF, you may switch into the `.bss' section and define
symbols as usual; see Note: `.section'.  You may only assemble
zero values into the section.  Typically the section will only contain
symbol definitions and `.skip' directives (Note: `.skip'.).