programs into the system C compiler and interpreting the generated
error messages, debug information, and object files. In practice,
parsing these is significantly less work and more robust than parsing
C source.

Cgo first invokes gcc -E -dM on the preamble, in order to find out
about simple #defines for constants and the like. These are recorded
for later use.

Go <code>const</code> declarations defined in the current package.
Go assembly should avoid making assumptions about the layout of Go
types and instead use these constants.
This improves the readability of assembly code, and keeps it robust to
changes in data layout either in the Go type definitions or in the
layout rules used by the Go compiler.
</p>

<p>
Constants are of the form <code>const_<i>name</i></code>.