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* doc/autoconf.texi (Invoking autom4te): End the option table,

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fixing a bug introduced by the previous patch.
(Limitations of Make): Add a 'target lookup' subentry in the
'VPATH' entry.  Rewrite all `make' occurences as `@command{make}'.
This commit is contained in:
Alexandre Duret-Lutz 2002-07-31 07:09:11 +00:00
parent a4865e2e2e
commit 738c678f2a
2 changed files with 162 additions and 55 deletions
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@ -1,3 +1,10 @@
2002-07-31 Alexandre Duret-Lutz <duret_g@epita.fr>
* doc/autoconf.texi (Invoking autom4te): End the option table,
fixing a bug introduced by the previous patch.
(Limitations of Make): Add a 'target lookup' subentry in the
'VPATH' entry. Rewrite all `make' occurences as `@command{make}'.
2002-07-29 Mark D. Roth <roth@feep.net>
* bin/autom4te.in: Remove --include-envvar and --site-macro-subdir
@ -29,7 +36,7 @@
* autoconf.texi (Limitations of Make, Making testsuite Scripts):
Untabify, since tabs are not enjoyed by texi2dvi and makeinfo.
2002-07-23 Paul Eggert <eggert@twinsun.com>
* lib/m4sugar/m4sh.m4 (_AS_PATH_SEPARATOR_PREPARE):

208
doc/autoconf.texi
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@ -7405,6 +7405,8 @@ create Autoconf executable configure scripts.
Prepend directory @var{dir} to the search path. This is used to include
the language-specific files before any third-party macros.
@end table
@cindex @file{autom4te.cfg}
As an example, if Autoconf is installed in its default location,
@file{/usr/local}, running @samp{autom4te -l m4sugar foo.m4} is
@ -10219,20 +10221,20 @@ on SunOS 4.1.3 when the empty file is on an @sc{nfs}-mounted 4.2 volume.
@node Limitations of Make
@section Limitations of Make
Make itself suffers a great number of limitations, only a few of which
being listed here. First of all, remember that since commands are
executed by the shell, all its weaknesses are inherited@enddots{}
@command{make} itself suffers a great number of limitations, only a few
of which being listed here. First of all, remember that since commands
are executed by the shell, all its weaknesses are inherited@enddots{}
@table @asis
@item @code{$<}
@sc{posix} says that the @samp{$<} construct in makefiles can be used
only in inference rules and in the @samp{.DEFAULT} rule; its meaning in
ordinary rules is unspecified. Solaris 8's Make for instance
ordinary rules is unspecified. Solaris 8's @command{make} for instance
will replace it with the argument.
@item Leading underscore in macro names
Some Makes don't support leading underscores in macro names, such as on
NEWS-OS 4.2R.
Some @command{make}s don't support leading underscores in macro names,
such as on NEWS-OS 4.2R.
@example
$ @kbd{cat Makefile}
@ -10264,13 +10266,14 @@ test:
@end example
@noindent
shows @code{FOO} equal to @code{one BAR = two}. Other Makes sensibly
let a backslash continue only to the immediately following line.
shows @code{FOO} equal to @code{one BAR = two}. Other @command{make}s
sensibly let a backslash continue only to the immediately following
line.
@item Escaped newline in comments
According to @sc{posix}, Makefile comments start with @code{#} and
continue until an unescaped newline is reached.
According to @sc{posix}, @file{Makefile} comments start with @code{#}
and continue until an unescaped newline is reached.
@example
% @kbd{cat Makefile}
@ -10308,10 +10311,10 @@ line with @code{#}, not only the first.
@item @code{make macro=value} and sub-@command{make}s.
A command-line variable definition such as @code{foo=bar} overrides any
definition of @code{foo} in the @file{Makefile}. Some Make
implementations (such as @sc{gnu} Make) will propagate this override to
sub-invocations of @command{make}, this is allowed but not required by
@sc{posix}.
definition of @code{foo} in the @file{Makefile}. Some @command{make}
implementations (such as @sc{gnu} @command{make}) will propagate this
override to sub-invocations of @command{make}, this is allowed but not
required by @sc{posix}.
@example
% @kbd{cat Makefile}
@ -10368,29 +10371,30 @@ You need to foresee all macros that a user might want to override if
you do that.
@item The @code{SHELL} macro
@cindex @code{SHELL} and Make
@cindex Make and @code{SHELL}
@cindex @code{SHELL} and @command{make}
@cindex @command{make} and @code{SHELL}
POSIX Makes internally use the @code{$(SHELL)} macro to spawn shell
processes and execute @file{Makefile} rules. This is a built-in
macro supplied by Make, but it can be modified from the Makefile or a
command-line argument.
@sc{posix}-compliant @command{make}s internally use the @code{$(SHELL)}
macro to spawn shell processes and execute @file{Makefile} rules. This
is a built-in macro supplied by @command{make}, but it can be modified
from the @file{Makefile} or a command-line argument.
Not all Makes will define this @code{SHELL} macro. OSF/Tru64 Make is
an example; this implementation will always use @code{/bin/sh}. So it's
a good idea to always define @code{SHELL} in your @file{Makefile}s. If
you use Autoconf, do
Not all @command{make}s will define this @code{SHELL} macro. OSF/Tru64
@command{make} is an example; this implementation will always use
@code{/bin/sh}. So it's a good idea to always define @code{SHELL} in
your @file{Makefile}s. If you use Autoconf, do
@example
SHELL = @@SHELL@@
@end example
@sc{posix}-compliant makes should never acquire the value of $(SHELL)
from the environment, even when @code{make -e} is used (otherwise, think
about what would happen to your rules if @code{SHELL=/bin/tcsh}).
@sc{posix}-compliant @command{make}s should never acquire the value of
$(SHELL) from the environment, even when @code{make -e} is used
(otherwise, think about what would happen to your rules if
@code{SHELL=/bin/tcsh}).
However not all Make implementations will make this exception.
For instance it's not surprising that OSF/Tru64 Make doesn't
However not all @command{make} implementations will make this exception.
For instance it's not surprising that OSF/Tru64 @command{make} doesn't
protect @code{SHELL}, since it doesn't use it.
@example
@ -10414,9 +10418,9 @@ bar
Never put comments in a rule.
Some Makes treat anything starting with a tab as a command for the
current rule, even if the tab is immediately followed by a @code{#}.
The Make from Tru64 Unix V5.1 is one of them. The following
Some @command{make} treat anything starting with a tab as a command for
the current rule, even if the tab is immediately followed by a @code{#}.
The @command{make} from Tru64 Unix V5.1 is one of them. The following
@file{Makefile} will run @code{# foo} through the shell.
@example
@ -10426,12 +10430,12 @@ all:
@item The @file{obj/} subdirectory.
@cindex @file{obj/}, subdirectory
@cindex BSD make and @file{obj/}
@cindex BSD @command{make} and @file{obj/}
Never name one of your subdirectories @file{obj/} if you don't like
surprises.
If an @file{obj/} directory exists, BSD make will enter it
If an @file{obj/} directory exists, BSD @command{make} will enter it
before reading @file{Makefile}. Hence the @file{Makefile} in the
current directory will not be read.
@ -10474,14 +10478,14 @@ exit status: 0
@item @code{VPATH}
@cindex @code{VPATH}
There is no @code{VPATH} support specified in @sc{posix}. Many Makes
have a form of @code{VPATH} support, but its implementation is not
consistent amongst Makes.
There is no @code{VPATH} support specified in @sc{posix}. Many
@command{make}s have a form of @code{VPATH} support, but its
implementation is not consistent amongst @command{make}s.
Maybe the best suggestion to give to people who need the @code{VPATH}
feature is to choose a Make implementation and stick to it. Since the
resulting @file{Makefile}s are not portable anyway, better choose a
portable Make (hint, hint).
feature is to choose a @command{make} implementation and stick to it.
Since the resulting @file{Makefile}s are not portable anyway, better
choose a portable @command{make} (hint, hint).
Here are a couple of known issues with some @code{VPATH}
implementations.
@ -10491,16 +10495,17 @@ implementations.
@item @code{VPATH} and double-colon rules
@cindex @code{VPATH} and double-colon rules
@cindex double-colon rules and @code{VPATH}
Any assignment to @code{VPATH} causes Sun Make to only execute the first
set of double-colon rules. (This comment has been here since 1994 and
the context has been lost. It's probably about SunOS 4. If you can
reproduce this, please send us a test case for illustration.)
Any assignment to @code{VPATH} causes Sun @command{make} to only execute
the first set of double-colon rules. (This comment has been here since
1994 and the context has been lost. It's probably about SunOS 4. If
you can reproduce this, please send us a test case for illustration.)
@item @code{$<} in inference rules:
@cindex suffix rules, @code{$<}, and @code{VPATH}
@cindex @code{$<}, inference rules, and @code{VPATH}
@cindex @code{VPATH}, inference rules, and @code{$<}
An implementation of make would not prefix @code{$<} if this
An implementation of @command{make} would not prefix @code{$<} if this
prerequisite has been found in a @code{VPATH} dir. This means that
@example
@ -10522,8 +10527,8 @@ VPATH = ../src
@end example
This kludge was introduced in Automake in 2000, but the exact context
have been lost. If you know which make implementation is involved here,
please drop us a note.
have been lost. If you know which @command{make} implementation is
involved here, please drop us a note.
@item @code{$<} not supported in explicit rules
@ -10546,9 +10551,9 @@ foo.o: foo.c
@cindex @code{VPATH} and automatic rule rewriting
@cindex automatic rule rewriting and @code{VPATH}
Some Make implementations, such as SunOS Make, will
search prerequisites in @code{VPATH} and rewrite all their occurrences in
the rule appropriately.
Some @command{make} implementations, such as SunOS @command{make}, will
search prerequisites in @code{VPATH} and rewrite all their occurrences
in the rule appropriately.
For instance
@ -10562,7 +10567,7 @@ foo.o: foo.c
would execute @code{cc -c ../src/foo.c -o foo.o} if @file{foo.c} was
found in @file{../src}. That sounds great.
However, for the sake of other Make implementations, we can't
However, for the sake of other @command{make} implementations, we can't
rely on this, and we have to search @code{VPATH} manually:
@example
@ -10573,7 +10578,7 @@ foo.o: foo.c
@noindent
However the "prerequisite rewriting" still applies here. So if
@file{foo.c} is in @file{../src}, SunOS Make will execute
@file{foo.c} is in @file{../src}, SunOS @command{make} will execute
@example
@code{cc -c `test -f ../src/foo.c || echo ../src/`foo.c -o foo.o}
@ -10675,12 +10680,12 @@ install-HEADERS: $(HEADERS)
@end example
@item OSF/Tru64 make creates prerequisite directories magically
@item OSF/Tru64 @command{make} creates prerequisite directories magically
@cindex @code{VPATH} and prerequisite directories
@cindex prerequisite directories and @code{VPATH}
When a prerequisite is a sub-directory of @code{VPATH}, Tru64
Make will create it in the current directory.
@command{make} will create it in the current directory.
@example
% @kbd{mkdir -p foo/bar build}
@ -10706,6 +10711,101 @@ all : foo/bar
The above @command{command} will be run on the empty @file{foo/bar}
directory that was created in the current directory.
@item target lookup
@cindex @code{VPATH}, resolving target pathnames
GNU @command{make} uses a rather complex algorithm to decide when it
should use files found via a @code{VPATH} search. @xref{Search
Algorithm,, How Directory Searches are Performed, make, The GNU Make
Manual}.
If a target needs to be rebuilt, GNU @command{make} discards the
filename found during the @code{VPATH} search for this target, and
builds the file locally using the filename given in the @file{Makefile}.
If a target does not need to be rebuilt, GNU @command{make} uses the
filename found during the @code{VPATH} search.
Other @command{make} implementations, like BSD @command{make}, are
easier to describe: the filename found during the @code{VPATH} search
will be used whether the target needs to be rebuilt or not. Therefore
new files are created locally, but existing files are updated at their
@code{VPATH} location.
When attempting a @code{VPATH} build for an autoconfiscated package
(e.g, @code{mkdir build; ../configure}), this means the GNU
@command{make} will build everything locally in the @file{build}
directory, while BSD @command{make} will build new files locally and
update existing files in the source directory.
@example
% @kbd{cat Makefile}
VPATH = ..
all: foo.x bar.x
foo.x bar.x: newer.x
@@echo Building $@@
% @kbd{touch ../bar.x}
% @kbd{touch ../newer.x}
% @kbd{make} # GNU make
Building foo.x
Building bar.x
% @kbd{pmake} # BSD make
Building foo.x
Building ../bar.x
@end example
Another point worth mentioning is that once GNU @command{make} has
decided to ignore a @code{VPATH} filename (e.g. it ignored
@file{../bar.x} in the above example) it will continue to ignore it when
the target occurs as a prerequisite of another rule.
The following example shows that GNU @command{make} does not look up
@file{bar.x} in @code{VPATH} before performing the @code{.x.y} rule,
because it ignored the @code{VPATH} result of @file{bar.x} while running
the @code{bar.x: newer.x} rule.
@example
% @kbd{cat Makefile}
VPATH = ..
all: bar.y
bar.x: newer.x
@@echo Building $@@
.SUFFIXES: .x .y
.x.y:
cp $< $@@
% @kbd{touch ../bar.x}
% @kbd{touch ../newer.x}
% @kbd{make} # GNU make
Building bar.x
cp bar.x bar.y
cp: cannot stat `bar.x': No such file or directory
make: *** [bar.y] Error 1
% @kbd{pmake} # BSD make
Building ../bar.x
cp ../bar.x bar.y
@end example
Note that if you drop away the command from the @code{bar.x: newer.x}
rule, things will magically start to work: GNU @command{make} knows that
@code{bar.x} hasn't been updated, therefore it doesn't discard the
result from @code{VPATH} (@file{../bar.x}) in succeeding uses.
@example
% @kbd{cat Makefile}
VPATH = ..
all: bar.y
bar.x: newer.x
.SUFFIXES: .x .y
.x.y:
cp $< $@@
% @kbd{touch ../bar.x}
% @kbd{touch ../newer.x}
% @kbd{make} # GNU make
cp ../bar.x bar.y
% @kbd{rm bar.y}
% @kbd{pmake} # BSD make
cp ../bar.x bar.y
@end example
@end table
@end table