MAKEPP_SCANNING(1) Makepp MAKEPP_SCANNING(1)NAMEmakepp_scanning-- How makepp finds include files and other hidden
dependencies
DESCRIPTION
Makepp can determine additional dependencies or targets for certain
commands that it knows something about. This is especially important
for C/C++ compilation, where it is too error-prone to list manually all
of the include files that a given source file depends on. By looking
at the compilation command and the source files themselves, makepp is
able to determine accurately which object files need to be rebuilt when
some include file changes.
Example: Given a rule
foo.o: # Usually %.o: %.c, just for illustration
time -p /bin/libtool -bar /usr/bin/cc -c -I somewhere foo.c
makepp knows that "time" and "libtool" must be skipped and that "cc" is
the actual command to be parsed here. It understands that foo.c is the
input file and thus a dependency of this rule. Moreover it will scan
that file looking for include statements, also in directory somewhere,
because it understood the command options.
Actually there are three steps to what is historically known as
scanning:
1. The rule action is split into lines (continuation lines count as
one). Each line (except builtins and Perl blocks) is lexically
analyzed as one or more Shell commands. Redirections are
recognized as inputs or outputs to this rule. The first word of
each command is looked up (with its directory part but, if not
found, again without it) to find a parser for it. These become
optional dependencies, they are built if possible, but ignored if
not found, as makepp can't know which part of a complex command is
actually run.
Commands in backquotes are analyzed but not executed. (Often
execution is important, but this would be a major interference by
makepp.) It is better style to avoid them. Instead have makepp
run the command at most once by assigning it in this special way:
XYZFLAGS ;= $(shell pkg-config --cflags xyz)
Currently there is only one lexer class, which understands Bourne
Shell. To better handle C Shell or "command.com", subclasses might
be created. However, much syntax is similar enough to not warrant
this. Get in touch if you want to contribute either.
2. For known commands the corresponding command parser (also referred
to just as parser) analyzes the important options and arguments.
The available ones are described below.
Even if no specialized parser was found, the generic one makes the
command executable an input of this rule. You can change that with
the --no-path-executable-dependencies command option.
3. If the parser recognized any input files, they get sent to the
scanner chosen by the parser. It finds further inputs by looking
for "#include" or comparable statements.
This is the most expensive step. All the results get cached to
avoid repeating it unnecessarily.
If makepp thinks it's compiling a C/C++ source but can't find a parser,
it will give a warning message to let you know. This usually means
that you buried your compiler command too deeply in the action for
makepp to find it. For example, I have seen rules like this:
%.o: %.c
@echo Compiling $< now; obscure_wrapper gcc -c $< $(CFLAGS) -o $@
The first words of the actions here are "echo" and "obscure_wrapper",
for which there are no parsers, so makepp will not scan for include
files in this case. You can ignore the prefixed command by:
register-parser obscure_wrapper skip-word
The following sections document the built in parsers and scanners. In
the name you can use "-" interchangeably with "_".
SCANNERS (PARSERS)
The various scanners must be chosen by a command parser, which is given
in parentheses:
C/C++ compilation (c-compilation, gcc-compilation)
The C/C++ scanner, handles both languages indifferently. In fact it
looks only at preprocessor statements, so it can be used for quite a
few languages. The parser that activates it has a special variant for
gcc's many options, which gets chosen if the command name includes the
string "gcc" or g++. If compilers for other languages with C
preprocessor use the same options as the C compiler (at least "-I")
then this parser works fine.
It looks at the command for "-Idir" options specifying the include path
or "-Ldir" options specifying the link path. It then scans any source
files for "#include" directives, and also looks at the command line to
see if there are any source files or libraries mentioned which are not
listed as dependencies. It recognizes these by their extension.
This scanner gives a warning message if files included with
"#include "file.h"" are not found, or not buildable by makepp, in the
include path, or in the directory containing the file which is
"#includ"ing, or in /usr/include. No warning is given if a file
included with "#include <file.h>" is not found. Makepp assumes it is
in some system include directory that the compiler knows about, and
that files in system include directories won't change.
In addition, files in /usr/include, /usr/local/include,
/usr/X11R6/include, and any other directory which is not writable are
not scanned to see what they include. Makepp assumes that these files
won't change. (If you're running as root, the writability test is
performed with the UID and GID of the directory you ran makepp from.
This is so compiling a program as an ordinary user and then doing
"makepp install" as root won't cause extra directories to be scanned.)
This is a fairly simple-minded scanner. It will get confused if you do
things like this:
#ifdef INCLUDE_THIS
#include "this.h"
#endif
because it doesn't know about preprocessor conditionals. This is
usually harmless; it might cause additional extra files to be labeled
as dependencies (occasionally causing unnecessary rebuilds), or else it
might cause makepp to warn that the include file was not found. You
can either ignore the warning messages, or put an empty file "this.h"
out there to shut makepp up.
If your compiler has a funny name, you can say either of
register-parser obscure_c_compiler c-compilation
register-parser obscure_gcc_alias gcc-compilation
Embedded SQL C/C++ compilation (esql-compilation)
These commands, which come with the various databases, preprocess
special sections in otherwise C/C++-like sources, and produce C/C++
headers and sources. This finds EXEC SQL INCLUDE "filename" or
$INCLUDE "filename" directives.
These preprocessors are recognized: Altibase APRE*C/C++ (apre),
CASEMaker DBMaker (dmppcc), Firebird / InterBase (gpre), IBM DB2 (db2
precompile, db2 prep) & Informix ESQL/C (esql), Ingres (esqlc), Mimer
(esql), Oracle (proc), PostgreSQL (ecpg) & YARD (yardpc). If your
preprocessor is not recognized, you can say
register-parser obscure_esqlc_preprocessor esql-compilation
This will however only handle the style common to Informix and others:
Command arguments ending in ".ec" are files to be scanned, "-I" defines
the include path and EXEC SQL INCLUDE directives without a suffix get
".h" appended.
Swig (swig)
Swig (Simplified Wrapper and Interface Generator, http://www.swig.org/)
is a program that converts a C/C++ header file into the wrapper
functions needed to make your code callable from a variety of other
languages, such as Perl, Python, Tcl, C#, Ruby, OCaml, and probably
some others that I don't know about.
Makepp understands and parses the swig command line, looking for "-I"
and "-l" options. It also knows how to scan swig's interface
definition files (.i files) looking for %include, %import, and also
"#include" if "-includeall" is in effect.
If your swig has a funny name, you can say
register-parser obscure_swig_alias swig
Vera and Verilog (vcs_compilation)
If you design hardware, this will come in handy.
Ignorable wrappers (skip-word, shell)
Makepp recognizes the following command words and many more and skips
over them appropriately in in its search for the correct scanner:
"condor_compile", "distcc", "ignore_error", "libtool", "noecho"
"purify".
There is a variant of this which finds the nested commands in "sh -c
'command1; command2'".
If you have more such commands, you can say
register-parser command skip-word
Libtool
Libtool is a very clever compilation system that greatly simplifies
making shared libraries by hiding all the system-dependent details away
in a shell script. The only difficulty is that the library binary
files are not actually stored in the same directory as the output
file--libtool actually creates a subdirectory, ".libs", which contains
the real files. This is ordinarily not a problem, but makepp has to
know where the real binaries are if it is to link them in from a
repository. At the moment, libtool libraries (".la" files) are not
linked in from repositories; they are always rebuilt if needed. Also,
makepp at the moment is not able to use the dependency information that
is stored inside the ".la" file itself. This will hopefully change
soon.
Suppressing the scan (none)
Sometimes you may not want a rule or a certain command to be parsed.
You can turn off parsing and thereby scanning with
register-parser cc none
RELATED OPTIONS
Quickscan and smartscan
The ":quickscan" and ":smartscan" rule options, if applicable, affect
the way that files are scanned.
In ":quickscan" mode (the default), all include directives are assumed
active. This allows for very efficient scanning.
In ":smartscan" mode, an attempt is made to interpret macros and
expressions so that inactive include directives are ignored. For
example, the executable produced by compiling the following C program
ought not to depend on foo.h:
#if 0
#include "foo.h"
#endif
int main() { return 0; }
CUSTOM SCANNERS
You can specify your own parser either in a rule option like ":parser
foo", or by using the "register_parser" or "register_command_parser"
statements.
Either way, as described under "register_parser", there you must
directly or indirectly (via a class) specify a function that creates a
parser object. This object will usually create a scanner object for
files, and feed it with its findings from the command line options.
These two objects will call the parser's "add_*_dependency" methods
which forward the information to the somewhat more complicated
"Mpp::Lexer::add_*_dependency" utility functions.
However your parser function can also do this work itself for simple
cases. There are a couple of special return values if this function
doesn't return a parser object:
"undef"
The scan info is not cacheable and must be recalculated next time
the rule's target needs to be built.
"p_none, p_skip_word" or "p_shell"
These are in fact numeric constants, which tell the lexer to do the
work of these pseudo-parsers.
any reference, e.g. "\1"
This is equivalent to returning a parser object of the
"Mpp::CommandParser" base class, which will only additionally make
the command executable itself a dependency.
In most cases, objects of type "Mpp::CommandParser" should instantiate
at least one object of type "Mpp::Scanner". The "Mpp::Scanner" base
class takes care of the distinction between quickscan and smartscan.
Note that the behavior of "Mpp::Scanner" can be markedly affected by
this distinction, but that should be transparent to the derived class
if it is well-formed. New derived "Mpp::Scanner" classes ought to be
tested in both modes.
If you write your own "Mpp::Scanner" class, you should also base your
rescanning decision on the build info "RESCAN". This gets set by
"makeppreplay" after signing files without scanning. So despite the
signatures being consistent, a rescan is still necessary. If your
"Mpp::Scanner" uses the inherited "scan_file1" method, you're probably
fine.
For more details, refer to the respective class documentation. For
examples, see "Mpp::CommandParser::Gcc" and "Mpp::CommandParser::Vcs".
Look at the "p_" functions in Mpp/Subs.pm which get aliased into their
respective classes as "factory" when loaded.
Caching scanner info
If the all of the scanner's important side effects are effected through
calls to methods of the "Mpp::CommandParser" base class, then those
side effects can be cached in the build info file, so that they can be
played back by a subsequent invocation of makepp without doing all of
the costly scanning work. This can save quite a bit of time,
especially in smartscan mode.
If the scanner has other important side effects, then it should call
the "Rule" object's mark_scaninfo_uncacheable method. Otherwise, the
scanner info retrieved from the build info may be inaccurate, causing
the build result possibly to be incorrect. This method is called
automatically when a value from the %parsers hash does not return an
object of type "Mpp::CommandParser", or when the parser is specified
with a rule option and the "p_*" routine does not return an object of
type "Mpp::CommandParser".
Cached scan info is invalidated using criteria similar to those used
for determining when the target is out of date. Similarly, it can be
retrieved from a repository using criteria similar to those used for
determining when a target can be linked in from a repository.
You can force makepp to ignore the cached scanner info with the
"--force-rescan" option. This is useful when a broken scanner may have
caused incorrect scanner info to be cached.
Ad Hoc Scanner
Often you will have just one or few files which contain dependency
information. You don't want to write this into a makefile redundantly
(since redundancy later often leads to inconsistencies when one update
gets forgotten). But you also don't want to write a Mpp::Scanner? As
a workaround you can generate an include file on the fly. For example
Qt has .qrc files which can look like:
<RCC>
<qresource prefix="...">
<file>abc</file>
<file>xyz</file>
...
If you adhere to the above layout, you can transform the relevant lines
into a makepp include file, which gets automatically created by being
included.
%.qrc.makepp: %.qrc
&grep 's!<RCC>\n!$(stem).cc:! || s! *<file>! ! && s!</file>\n!!' $(input) -o $(output)
include $(wildcard *.qrc) # .makepp is appended automatically
The drawback is that you begin building while reading the makefile. So
the --stop-after-loading command option will not be very useful.
perl v5.20.3 2012-02-07 MAKEPP_SCANNING(1)
