Word - Using as
Description: Using as

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### 7.122 `.word` expressions

This directive expects zero or more expressions, of any section, separated by commas.

The size of the number emitted, and its byte order, depend on what target computer the assembly is for.

> Warning: Special Treatment to support Compilers

Machines with a 32-bit address space, but that do less than 32-bit addressing, require the following special treatment. If the machine of interest to you does 32-bit addressing (or doesn't require it; see Machine Dependencies), you can ignore this issue.

In order to assemble compiler output into something that works, `as` occasionally does strange things to ‘`.word`’ directives. Directives of the form ‘`.word sym1-sym2`’ are often emitted by compilers as part of jump tables. Therefore, when `as` assembles a directive of the form ‘`.word sym1-sym2`’, and the difference between `sym1` and `sym2` does not fit in 16 bits, `as` creates a secondary jump table, immediately before the next label. This secondary jump table is preceded by a short-jump to the first byte after the secondary table. This short-jump prevents the flow of control from accidentally falling into the new table. Inside the table is a long-jump to `sym2`. The original ‘`.word`’ contains `sym1` minus the address of the long-jump to `sym2`.

If there were several occurrences of ‘`.word sym1-sym2`’ before the secondary jump table, all of them are adjusted. If there was a ‘`.word sym3-sym4`’, that also did not fit in sixteen bits, a long-jump to `sym4` is included in the secondary jump table, and the `.word` directives are adjusted to contain `sym3` minus the address of the long-jump to `sym4`; and so on, for as many entries in the original jump table as necessary.