5.6 Interrupting or Killing `make'
If `make' gets a fatal signal while a command is executing, it may
delete the target file that the command was supposed to update. This is
done if the target file's last-modification time has changed since
`make' first checked it.
The purpose of deleting the target is to make sure that it is remade
from scratch when `make' is next run. Why is this? Suppose you type
`Ctrl-c' while a compiler is running, and it has begun to write an
object file `foo.o'. The `Ctrl-c' kills the compiler, resulting in an
incomplete file whose last-modification time is newer than the source
file `foo.c'. But `make' also receives the `Ctrl-c' signal and deletes
this incomplete file. If `make' did not do this, the next invocation
of `make' would think that `foo.o' did not require updating--resulting
in a strange error message from the linker when it tries to link an
object file half of which is missing.
You can prevent the deletion of a target file in this way by making
the special target `.PRECIOUS' depend on it. Before remaking a target,
`make' checks to see whether it appears on the prerequisites of
`.PRECIOUS', and thereby decides whether the target should be deleted
if a signal happens. Some reasons why you might do this are that the
target is updated in some atomic fashion, or exists only to record a
modification-time (its contents do not matter), or must exist at all
times to prevent other sorts of trouble.
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