Linker emulation selection

A linker emulation is a "personality" of the linker, which gives the linker default values for the other aspects of the target system. In particular, it consists of

• the linker script
• the target
• several "hook" functions that are run at certain stages of the linking process to do special things that some targets require

The command to list valid linker emulation values is `ld -V'.

Sample values: `hp300bsd', `mipslit', `sun4'.

Ways to specify:

1. command line option: `-m' (see section `Options' in Using LD)
2. environment variable LDEMULATION
3. compiled-in DEFAULT_EMULATION from `Makefile', which comes from EMUL in `config/target.mt'