NAME¶
makepp_incompatibilities -- Incompatibilities between makepp and GNU make
DESCRIPTION¶
Makepp was designed to be as close as possible to GNU make
(<
http://www.gnu.org/software/make/manual/make.html>). GNU autotools
(<
http://www.gnu.org/software/automake/manual/automake.html>), CMake
(<
http://www.cmake.org/>), Premake
(<
http://industriousone.com/premake> and see remark below) or
handcrafted legacy build systems should be buildable with makepp. This is so
you can either migrate projects effortlessly. Or if you don't want to enjoy
all of makepp's advantages (e.g. so others can still build your project with
GNU make) while you profit from the reliability advantage for your
development.
However, because of the difference in philosophy, some of GNU make's or POSIX
make's
(<
http://pubs.opengroup.org/onlinepubs/009695399/utilities/make.html>)
features cannot be supported. A few have not been implemented because we
haven't had time. Most of the differences from GNU make are quite technical
and only rarely cause problems. Alas the workarounds for the short-comings of
traditional make are becoming more and more complex, and are giving makepp a
hard time.
In a nutshell, if it doesn't build out of the box, try:
makepp --no-warn makepp_simple_concatenation=1 makepp_percent_subdirs=1 \
--build-check=target_newer --last-chance-rules --no-remake-makefiles
If that succeeds, you can try to eliminate those arguments one by one. But if
that fails, try adding:
--traditional-recursive-make
If that also fails, the build system needs some tweaking to cooperate with
makepp. Even if some options described here make something buildable, it is
still recommended to adapt things slightly, so they become compatible out of
the box with both makes.
Forcing more POSIX or GNU make compatibility¶
Here are some command line possibilities for getting many legacy build systems
to work without modification. They cause makepp to emulate GNU make's behavior
precisely.
Compatibility via the option: "--build-check=target_newer"¶
By default, makepp will attempt to rebuild all targets if any of the
dependencies have changed since the last build, or if the command has changed
(see makepp_build_check for details). This is normally what you want.
Sometimes, however, you don't want the target to be rebuilt if it has been
modified apart from the control of makepp (e.g., by editing it, or by running
a program manually to make the file). You can force makepp to use the
traditional make algorithm, which only rebuilds if any of the targets are
newer than the dependencies, by adding this option to the command line.
Compatibility via the option: "--dont-build=config.status"¶
There are packages which try to autoconfigure themselves, or do other things,
which gmake ignores unless being asked to, like:
config.status : configure
./config.status --recheck
configure : configure.in aclocal.m4
autoconf
Most people don't even have "autoconf" installed, so conscientiously
doing everything by the rules, as makepp does, will fail. This option prevents
that, if you figure out what not to build.
Compatibility via the option: "--last-chance-rules"¶
Default rules (pattern rules with no pattern dependencies) are not normally
supported. Makepp instantiates all rules based on the existing files, so that
it is aware of every file that could be generated. Alas this way it does not
know how to instantiate a pattern rule with no pattern dependency. The
:last_chance mechanism partially remedies that. Where this is good enough for
legacy makefiles, this option allows turning it on globally.
Compatibility via the option: "--no-warn"¶
This one doesn't improve the result. Makepp will give warning messages for many
things which the traditional Unix make accepts without flinching. This is
because there are better ways to do them with makepp. If these warnings annoy
you, you can turn them off with this option.
Compatibility via the option: "--hybrid-recursive-make"¶
Recursive invocations of make are often considered to be an unsafe practice (see
"Better system for hierarchical builds" in makepp for details), but
they are extremely common in existing makefiles. Makepp supports recursive
make for backward compatibility; for new makefiles, it is much better to use
the "load_makefile" statement, or makepp's implicit makefile loading
mechanism.
In order to be able to use repositories for variant builds, and to help make
recursive invocations of make safer, makepp normally does not actually invoke
itself recursively even if you tell it to. Instead, a subprocess communicates
with the parent process, and the actual build is done by the parent process.
This works in most cases, but you may not invoke several makefiles from the same
directory, e.g., the following will not work:
target: dependencies
$(MAKE) -f other_makefile targets
In this case makepp notices it is loading a 2nd makefile and complains. With
this option instead it will fall back to the traditional way of building from
additional makefiles in a separate makepp process each.
Note: Technically loading several makefiles would be no problem, but they
usually have the same phony target names. Keeping that apart would mean a
complete redesign of makepp internals. However, this will work, but it is not
equivalent:
target: dependencies
cd subdir && $(MAKE) -f other_makefile targets
Compatibility via the option: "--traditional-recursive-make"¶
Sometimes the previous option is not enough, especially if the recursive
invocations use contradictory options. Makepp uses only one set of global
options, so a submake is not allowed to modify them, as that would also
pertain to other makefiles.
Adding this option to the command line, has the following undesirable side
effects:
- •
- Recursive makes do not internally execute in parallel, even if the parent
does. Unlike gmake there is no overall coordination of the number of
processes. This will not be implemented because this way of working is not
a design goal of makepp.
- •
- Recursive make processes do not know anything about repositories.
- •
- Each recursive make process produces its own log file, in the directory it
is invoked in, instead of producing one log file for the entire
build.
- •
- Since makepp usually builds more than traditional make deems necessary,
and since many build systems provide recursive calls in all directions,
this may lead to endless recursion. Makepp will pull the brake after 50
rounds and tell you how to increase that, in case you really have such
deep nesting.
Even with the "--traditional-recursive-make" option, the environment
variables "MAKEOVERRIDES" and "MFLAGS" are not set up, and
ignored, so makefiles that depend on those will not work.
A
Premake generated
Makefile is only a funny wrapper to a sub-make
invocation in the same directory. If you have some project target
XYZ
it will have a line like
@${MAKE} --no-print-directory -C . -f XYZ.make
In this case you can avoid the "--traditional-recursive-make" option
by directly invoking makepp with that "-f
XYZ.make" option.
Compatibility without the option: "--jobs= n"¶
Legacy makefiles will sometimes not list all dependencies, relying on the order
of execution to make them in time. In this situation makepp may manage to call
a rule before its dependencies have all been made. Then results may be better
with less, or even no parallel execution.
Compatibility via the variable: "makepp_simple_concatenation=1"¶
Rc-style substitution is the default way makepp performs variable substitution
into text strings because it very rarely breaks legacy makefiles and is often
useful in new makefiles. However, it does introduce occasional
incompatibilities in the substitution of variables not surrounded by spaces.
For example,
INCLUDE_PREFIX := -I/some/include/dir -I
INCLUDES := $(INCLUDE_PREFIX)/other/include/dir
will set "INCLUDES" to
"-I/some/include/dir/other/include/dir -I/other/include/dir"
if rc-style substitution is enabled, whereas GNU make would set it to
"-I/some/include/dir -I/other/include/dir". E.g., when
compiling Redis 2.6.5 it tries to run "printfgcc". Such a funny
concatenation of two commands is a strong indication that this variable is
needed to fall back to make semantics.
There is also an incompatibility in the handling of whitespace in a variable:
null :=
T := -o $(null) # T contains -o followed by one space.
OUTFILE = $(T)outfile
will set "OUTFILE" to "-ooutfile" if rc-style substitution
is enabled, whereas GNU make would set it to "-o outfile".
Both of these incompatibilities are removed by setting the
"makepp_simple_concatenation" variable. Note, however, that even
with "makepp_simple_concatenation", makepp still treats whitespace
incompatibly in some situations:
T := -o # Don't delete this comment.
GNU make sets "T" to contain "-o" followed by a space,
whereas makepp strips out the trailing space anyway. If you want the trailing
space, you must set "makepp_simple_concatenation" and also set
"T" using the technique involving a dummy variable such as
"null", as shown above.
Workaround option "--no-remake-makefiles"¶
Typical open source requires calling "configure" to create the
makefiles. But then these makefiles can contain rules to remake the makefile,
by calling some command. Makepp will happily comply and update it according to
the rule. But sometimes this is harmful, so just skip it.
Compatibility via the variable: "makepp_percent_subdirs=1"¶
By default, "%" in a pattern rule does not match directories. This
means that a rule like this:
%.o: %.c
$(CC) $(CFLAGS) -c $(input) -o $(output)
will not be applied to files like "../shared/xyz.c". If you want it to
match files in subdirectories too, then set the variable
"makepp_percent_subdirs=1" on the command line or near the beginning
of a makefile.
Compatibility via the environment variable: $MAKEPP_IGNORE_OPTS¶
Sometimes legacy recursive invocations pass options that makepp doesn't
understand. Hopefully the option is not important, but it prevents makepp from
running. With this environment variable you can ask makepp to silently ignore
certain options. The value shall be a space separated list of options, which
can come in 4 variants:
- --long=x
- A long option that expects an argument. This fact must be declared through
the equals sign, though the actual use may also separated by whitespace,
either "--long=bla" or "--long bla".
- --long
- A long option without an argument.
- -sx
- A short option that expects an argument. This fact must be declared by
adding something directly after the option, though the actual use may also
separated by whitespace, either "-sbla" or "-s
bla".
- -s
- A short option without an argument.
E.g. override makepp's -R option by one without an argument and accept gmake's
debug option with an argument:
export MAKEPP_IGNORE_OPTS='-R --debug=x'
Incompatibilities that require Makefile changes¶
- •
- Makefiles that explicitly call make prevent makepp from building
everything itself. Alas Perl's own "ExtUtils::MakeMaker" commits
the second of the following two forms of this mistake up to version 6.56
(Perl 5.12.1):
subdir:
cd subdir; make
MAKE = make
- •
- Setting the "VPATH" variable to some value implicitly calls
"vpath % value". "vpath" statements are emulated with
the repository mechanism. So, where gmake substitutes the path to the file
found in the vpath, makepp will instead link it symbolically to where it
is needed. Thus makepp will provide an unmodified string, which is usually
not a problem.
Targets in a vpath are not supported. (Gmake considers them if they are
newer than their dependencies, but if not, the target will be recreated in
the current directory -- rather inconsistent.) Unsetting vpaths is not
supported.
- •
- A pattern rule present later in a makefile overrides one that is present
earlier. This is backwards from GNU make.
- •
- The set of builtin implicit rules is somewhat different from those for GNU
make, though the variable names are largely compatible. The builtin rules
should successfully compile C/C++/Fortran programs, and in fact may be
able to guess the proper libraries in some cases too. Support for Modula-2
and RatFor and other rare languages is deliberately not present, because I
kept running into problems with GNU make's rules when I accidentally
reused the extensions for those languages.
- •
- An action prefix of "+" is silently ignored.
- •
- Archive members are not supported, and neither are the associated
automatic variables $%, "$(%D)", and "$(%F)".
- •
- There is no SCCS support.
- •
- Leading and trailing whitespace in variable assignments is ignored (even
if the whitespace is followed by a comment). For more details on
whitespace handling incompatibilities, see "Whitespace in
variables" in makepp_variables.
- •
- Makepp does not attempt to rebuild files included with the
"include" statement unless the makefile contains a rule for
building them before the include statement is seen. (It will attempt to
rebuild the makefile itself, however.) This is normally used for handling
include file dependencies, and is not as useful with makepp since you
don't need to do that anyway.
- •
- The "SHELL" variable is currently partially ignored. Makepp
always uses /bin/sh unless /usr/xpg4/bin/sh or
/sbin/xpg4/sh is found or unless you export the "SHELL"
variable in your makefile. But if you do, the command parser might not
fully understand what your shell command does. On Windows Strawberry or
ActiveState Perl you must instead set your SHELL variable before
calling makepp.
- •
- Dependencies of anything on the Makefile still work, but are usually
unnecessary. This is usually used to force a rebuild when compilation
options change. Makepp knows when build commands have changed without
anything special in the makefile; it stores this on a file-by-file basis.
If you change the makefile, it knows exactly which files need
recompilation.
- •
- Intermediate files are not deleted. (Because makepp insists on having all
of the file dates be the same as they were on the last build, intermediate
files must all be present or else rebuilds will occur.) There is no
special status accorded to intermediate files.
- •
- The only special target that is supported is ".PHONY" and
partially ".SUFFIXES". The remaining are simply ingored.
Specifically, GNU make has the following special targets:
- .SUFFIXES
- Makepp ignores ".SUFFIXES" except for the special case of
".SUFFIXES" with no dependencies, like this:
.SUFFIXES:
which tells it not to load any of its default rules.
- .INTERMEDIATE, .SECONDARY, .PRECIOUS
- No special status is accorded to intermediate files and so these targets
are not meaningful.
- .IGNORE
- This target is ignored. If you want to ignore errors, put the word
"ignore_error" (or a minus sign) in front of the command whose
exit status is to be ignored.
- .SILENT
- This target is ignored. If you want commands not to echo, put the word
"noecho" (or the "@" character) in front of the
command which is not supposed to be echoed, or use the
"--silent" option to makepp.
- .DELETE_ON_ERROR
- .EXPORT_ALL_VARIABLES
- .NOEXPORT
- .POSIX
- .DEFAULT
- These targets are not supported and are simply ignored.
- •
- The GNU make functions "eval", "flavor" and
"value" are not currently supported. You can achieve the same
thing as eval in a more straight-forward way with "$[...]"
variable or function expansion.
- •
- Double colon rules are not fully supported. (They cannot be: in makepp's
paradigm, there cannot be more than one way to update a target.)
Currently, each successive double colon rule for a given target simply
appends its command string and dependency list to the command string and
dependency list for this target. For example, if you write this:
a :: b
&cat b -o a
# Later in your makefile:
a :: c
&cat c -o >>a
it is exactly the same as if you had written
a : b c
&cat b -o a
&cat c -o >>a
This is certainly not what double colon rules are intended for, and it will
not always work, but it does work for targets like "clean" or
for all the stuff that ExtUtils::MakeMaker puts into its makefiles. Don't
count on it for anything other than legacy makefiles.
- •
- The "$(wildcard )" function matches not only files which
exist, but also files which do not yet exist, but which have a rule which
makepp has seen at the time the "$(wildcard )" function
is evaluated.
- •
- The "define" statement is supported, but handling of
"@" preceding it is done differently. Currently in makepp,
"@" in front of a variable which has a multi-line value will
only suppress echoing of the first line. For example,
define echo-lines
&echo line1 -o $@
&echo line2 -o>>$@
endef
x:
@$(echo-lines)
will not suppress printing of "&echo line2" as it does
in GNU make; it will only suppress printing of
"&echo line1".
- •
- Makepp does not support the following environment variables (it does not
set them up, and it just ignores them):
Incompatibilities in order of expression expansion¶
- •
- In makepp, rule actions are expanded before all of the dependencies are
guaranteed to have been built. You can work around this by changing rules
such as this:
foo: bar
genfoo < $(shell cat bar)
to this:
foo: bar
genfoo < `cat bar`
or this, which will make the file during the expansion:
foo: bar
genfoo < $(&cat $(make bar))
This is preferable here, because the file listed in bar is also a
dependency of this rule, and makepp can now catch it when lexically
analyzing the redirection.
- •
- Though I have not seen this used, GNU make allows the following:
colon = :
a$(colon) b
echo $^
Makepp expands "$(colon)" too late for this to work. However it
offers the alternative "$[colon]" syntax, which can do much more
than GNU make, because it is expanded very early.
"$(MAKE)" may include spaces¶
In an uninstalled makepp or if the platform doesn't seem to support starting a
Perl script by magic number or with "--traditional-recursive-make"
this variable will include at least one space. That is not a problem when
using it as a command. But when passing it as an unquoted parameter to a
script (as the Perl 5.14.0 build system does), it will tear it apart into
separate parameters, leading to confusion. So as a parameter it is safer to
quote it as '$(MAKE)'. which doesn't break backward compatibility.
Target-specific assignments don't propagate¶
Makepp's target-specific variables are slightly different from GNU make's in
that they only apply to the rule for the one file mentioned, and not to any of
its predecessors; see Target-specific assignments.
Parentheses or braces don't nest¶
Makepp ends expressions at the first matching parenthesis or brace. Instead of
this
$(somefunction ... ( ) ...) # GNU make style
you must use either of these
${somefunction ... ( ) ...} # GNU make compatible
$((somefunction ... ( ) ...)) # Makepp extension
This will probably be fixed in version 2.1, maybe optionally.
Minor points¶
- Pattern dependencies don't match phony targets
-
%.a: %.b; ...
$(phony x.b): ; ... # does not provide a way to build x.a
- Comments don't have continuation lines
-
# This is \
NOT a 2-line comment
Command line incompatibilities¶
Makepp supports a few of make's more useful command line options. The following,
however, are not supported:
- -d or --debug
- -f -
- Makepp's internal makefile objects are linked to file objects, so it can't
handle stdin.
- -i
- -l or --load-average or --max-load
- -m
- Makepp's "-m" option has to do with signature method selection,
whereas GNU make ignores -m.
- -p or --print-data-base
- -q or --question
- -R or --no-builtin-variables
- Makepp's "-R" option actually does something completely
different.
- -S --no-keep-going or --stop
- The "--stop" option stops (puts to sleep) makepp after learning
all the rules, so you can continue editing.
- -t or --touch
- -w or --print-directory
- This happens automatically.
- --warn-undefined-variables
Some of these can be easily supported if anyone cares.
Variable incompatibilities¶
Makepp looks in $PATH for a matching command to return for variables like
"$(CC)" or "$(CXX)", while GNU make has static defaults.
Also makepp gives preference to "gcc" and "g++" while
surprisingly GNU make returns "cc" for the former, but the same for
the latter. You can override these in the makefile, on the command line or by
exporting a variable of the same name before invoking makepp.