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HOWTO Understanding effects of build directory options on a relocatable MinGW GCC default's paths

1 Summury and purpose of this document

Although there are nor big TODO remaining for this document, some updates are still pending

Target of this document: trying to better understand the effect of build time options on the resulting MinGW GCC's default paths. This is done testing the effect of some configuration options. These tests target the wish to have a multi-arch singled-versioned and relocatable installation directory. Comments and analysies given in this document, all goes to this direction. This document may not fullfill expectations from peoples with other wishes.

Test builds are done on Windows (XP or whatever below and above will probably give the same result) using MinGW as the C compiler and mSys as the build environnement (this is mandatory to run configuration and make scripts).

The document is divided into two main parts: tests at build time and tests with a relocated installation directory (the bigest part).

2 Tests at build time

2.1 The build was done with the following options:

2.1.1 Script variables:

  • mypkgname=....
  • name=gcc
  • package=gcc-4.2.1-2
  • build=i386-mingw32
  • host=i386-mingw32
  • target=i386-mingw32
  • prefix=/<my-msys-personal-home-dir>/$name
  • temp=$name

2.1.2 Options:

  • --with-pkgversion=$mypkgname
  • --build=$build
  • --host=$host
  • --target=$target
  • --prefix=$prefix
  • --with-sysroot=$prefix/$target/test1
  • --with-local-prefix=$prefix/$target/test2
  • --with-build-sysroot=$prefix/$target/test3
  • --disable-rpath
  • --disable-version-specific-runtime-libs
  • --enable-languages=c
  • --enable-libada
  • --enable-threads
  • --disable-shared
  • --disable-sjlj-exceptions
  • --disable-win32-registry
  • --enable-nls
  • --disable-bootstrap
  • --with-gnu-gcc
  • --with-gnu-as
  • --with-gnu-ld
  • --with-stabs


Do not forget:

  • Sysroot is set to /<install-dir>/<arch>/test1
  • Local prefix is set to /<install-dir>/<arch>/test2
  • Build sysroot is set to /<install-dir>/<arch>/test3
  • Prefix will be refered as /<install-dir>

A native compiler will be built the same way as if it was a cross compiler, to have a cleaner installation (each archs beside of each others, even the native one).

You will see these test1, test2, test3 in some paths list later. Do not forget what it is standing for (see above).

The build was started frm a build directory beside the source directory, with an installation directory bside the two laters, the a make and a make install was runned. The installation directory initially only contains <arch> and <arch>/test1 and <arch>/test2 and <arch>/test3.

Some thing was then deduced from error messages during the build process.

The build process expect a mingw/include in <install-dir>/<arch>/test3 (the build sysroot directory). It has complained with this message :

> The directory that should contain system headers does not exist:
> /<install-dir>/<arch>/test3/mingw/include

This mingw/include directory is mandatory during the build process, but it may be empty (the build process can terminates normally with an empty mingw/include).

The build process obviously complains about missing includes. Some test were done to list all directory where theses includes may be found.

2.3 Includes search when configuring gcc during the build process:

  • Not searched in /<install-dir>/include
  • Searched in /<install-dir>/<arch>/include
  • Not searched in /<install-dir>/<arch>/test1/include (sysroot/include)
  • Not searched in /<install-dir>/<arch>/test1/mingw/include (sysroot/mingw/include)
  • Not searched in /<install-dir>/<arch>/test2/include (localprefix/include)
  • Not searched in /<install-dir>/<arch>/test2/mingw/include (localprefix/mingw/include)
  • Not searched in /<install-dir>/<arch>/test3/include (buildsysroot/include)
  • Searched in /<install-dir>/<arch>/test3/mingw/include (buildsysroot/mingw/include)

2.4 Comments on the latter

The <install-dir> did not contained any libs. The build still terminates normally.

Includes needed for the build process, are searched only in <arch>/include and in <build-sysroot>/mingw/include. It is worth to notice that <sysroot>/mingw/include is not searched nor is <sysroot>/include.

3 Tests on a relocated installation directory (get and drop anywhere)

Next, <install-dir> is renamed into an <reloc-dir>, to test how install relocation works.

3.1 The resulting gcc, after relocation, use the following default paths:

  • Install:
    • <install-dir>/lib/gcc/<arch>/<version>/
  • Programs:
    • <reloc-dir>/libexec/gcc/<arch>/<version>/
    • <reloc-dir>/libexec/gcc/
    • <install-dir>/libexec/gcc/<arch>/<version>/
    • <install-dir>/libexec/gcc/<arch>/<version>/
    • <install-dir>/libexec/gcc/<arch>/
    • <install-dir>/lib/gcc/<arch>/<version>/
    • <install-dir>/lib/gcc/<arch>/
    • /usr/libexec/gcc/<arch>/<version>/
    • /usr/libexec/gcc/<arch>/
    • /usr/lib/gcc/<arch>/<version>/
    • /usr/lib/gcc/<arch>/
    • <reloc-dir>/<arch>/bin/<arch>/<version>/
    • <reloc-dir>/<arch>/bin/
    • <install-dir>/<arch>/bin/<arch>/<version>/
    • <install-dir>/<arch>/bin/
  • Libraries:
    • <reloc-dir>/lib/gcc/<arch>/<version>/
    • <reloc-dir>/lib/gcc/
    • <install-dir>/lib/gcc/<arch>/<version>/
    • /usr/lib/gcc/<arch>/<version>/
    • <reloc-dir>/<arch>/lib/<arch>/<version>/
    • <reloc-dir>/<arch>/lib/
    • <install-dir>/<arch>/lib/<arch>/<version>/
    • <install-dir>/<arch>/lib/
    • <reloc-dir>/lib/<arch>/<version>/
    • <reloc-dir>/lib/
    • <install-dir>/lib/<arch>/<version>/
    • <install-dir>/lib/
    • <reloc-dir>/<arch>/test1/mingw/lib/<arch>/<version>/
    • <reloc-dir>/<arch>/test1/mingw/lib/
  • Includes:
    • <reloc-dir>/<arch>/test1<install-dir>/include
    • <install-dir>/lib/gcc/<arch>/<version>/include
    • <install-dir>/<arch>/include
    • <reloc-dir>/<arch>/test1/mingw/include
    • <reloc-dir>/lib/gcc/<arch>/<version>/include

3.2 Comments on the latter

Note: this list was obtained with “./gcc --print-search-dirs” and “./gcc -v -c test.c”, after reformating and canonicalization of paths, followed by some symbolic substitutions.

Note: cc1 received the following parameters for -prefix and -sysroot:

  • -iprefix <reloc-dir>/lib/gcc/<arch>/<version>/
  • -isysroot <reloc-dir>/<arch>/test1 (sysroot)

Suspected bug: Did you notice the first include path ? It seems there is a bug here. Two absolute paths are appended. I've meet it every time during all the teste I've made. I've also found some buggy paths concatenation in some Configure.log files. I dunno if it is a MinGW GCC bug or a configuration script bug or an mSys bug.

Note: some paths were printed with “/” as the path separator while some other was printed with “\” as the path separator. I've substitued all with “/” as MinGW GCC accept both.

Notice that <arch>/include only exist with the <install-dir> prefix. This may be a trouble (we will see later for the reason why).

Notice that the directory test3, which stands for --build-sysroot does not exist any more in the default search paths. It is only used at build time.

3.3 In the purpose of a relocatable installation, the list may be reduced to:

  • Programs:
    • <reloc-dir>/libexec/gcc/<arch>/<version>/
    • <reloc-dir>/libexec/gcc/
    • <reloc-dir>/<arch>/bin/<arch>/<version>/
    • <reloc-dir>/<arch>/bin/
  • Libraries:
    • <reloc-dir>/lib/gcc/<arch>/<version>/
    • <reloc-dir>/lib/gcc/
    • <reloc-dir>/<arch>/lib/<arch>/<version>/
    • <reloc-dir>/<arch>/lib/
    • <reloc-dir>/lib/<arch>/<version>/
    • <reloc-dir>/lib/
    • <reloc-dir>/<arch>/test1/mingw/lib/<arch>/<version>/
    • <reloc-dir>/<arch>/test1/mingw/lib/
  • Includes:
    • <reloc-dir>/<arch>/test1/mingw/include
    • <reloc-dir>/lib/gcc/<arch>/<version>/include

3.4 Comments on the latter

Note: this list is obtained removing all paths starting with <install-dir> and paths which are POSIX paths (ex. “/usr/libexec”), thus keeping only paths starting with <reloc-dir>. The first include buggy path was removed too (unusable anyway).

For options recieved by cc1:

  • -iprefix <reloc-dir>/lib/gcc/<arch>/<version>/
  • -isysroot <reloc-dir>/<arch>/test1 (sysroot)

It seems the directory mingw in expected in test1 (unlike at build time, where it was expected in test3).
Remind that test1 stands for sysroot.

3.5 In the purpose to have a clean single versioned relocatable installation, the list may be reduced again to:

  • Programs:
    • <reloc-dir>/libexec/gcc/
    • <reloc-dir>/<arch>/bin/
  • Libraries:
    • <reloc-dir>/lib/gcc/
    • <reloc-dir>/<arch>/lib/
    • <reloc-dir>/lib/
    • <reloc-dir>/<arch>/test1/mingw/lib/
  • Includes:
    • <reloc-dir>/<arch>/test1/mingw/include

3.6 Comments on the latter

Note: this list was obtained removing all paths containing <version>.

In the purpose of a multi-arch single versioned and relocatable installation, we notice there gonna be a trouble with the default include paths : it only looks in <reloc-dir>/<arch>/test1/mingw/include.

For options recieved by cc1: -isysroot <reloc-dir>/<arch>/test1 (sysroot)

-prefix, which was <reloc-dir>/lib/gcc/<arch>/<version>/ (see §3.3 and §3.4), use a versioned directory only.

The favorite path for programs would probably be <reloc-dir>/<arch>/bin/, the favorite paths for libs would probably be <reloc-dir>/lib/ and <reloc-dir>/<arch>/lib/. There are no good candidates for includes (an <arch>/include would be nice).

A special specs file may be needed to workaround the default include paths problem (see §9 later).

4 Using the same path for both sysroot and build-sysroot

4.1 The new context

In §2.2, we've seen that the build process expect a mingw/include directory in build-sysroot, while it does not expect it in sysroot. Further more in §2.3, we've seen that sysroot/include and sysroot/mingw/include were not searched for includes and in §3.1 and §3.2, that the build-sysroot does not exist in default search paths. As this seem a bit weird that sysroot was not working the same way as build-sysroot, another test was runned, using the same path for both --with-sysroot and --with-build-sysroot and run all the same tests as for from §2 to §3. Note: to not be too much borring, only the differences will be given.

The context can be sumarized like this : test3 does not exist any more and --with-build-sysroot has the same value as --with-sysroot.

  • The build process now expect mingw/include in test1.
  • test1/mingw/include is now searched (sysroot/mingw/include)

Do not not forget that test3 does not exist anymore in this context.

4.2 Includes required at build time are now searched in:

  • Searched in /<install-dir>/<arch>/include
  • Searched in /<install-dir>/<arch>/test1/mingw/include (sysroot/mingw/include)
  • Not searched in any other locations beneath <intall-dir>

4.3 Default paths for the resulting MinGW GCC

Installation, programs and libraries paths, are the same as in §3.1. Includes paths differs from the ones in §3.1

In §3.1, include paths were:

  1. <reloc-dir>/<arch>/test1<install-dir>/include
  2. <install-dir>/lib/gcc/<arch>/<version>/include
  3. <install-dir>/<arch>/include
  4. <reloc-dir>/<arch>/test1/mingw/include
  5. <reloc-dir>/lib/gcc/<arch>/<version>/include

Now the include search paths list is:

  1. <reloc-dir>/<arch>/test1<install-dir>/include
  2. <install-dir>/lib/gcc/<arch>/<version>/include
  3. <install-dir>/<arch>/include
  4. <reloc-dir>/lib/gcc/<arch>/<version>/include
  5. <reloc-dir>/<arch>/test1/mingw/include

4.4 Comments on the latter

The item initial item #4 is now at position #5 and the initial item #5 is now at position #4. The only difference is the permutation of <reloc-dir>/<arch>/test1/mingw/include and <reloc-dir>/lib/gcc/<arch>/<version>/include which are still the last in the search list.

4.5 Default paths for a relocatable MinGW GCC

Paths are the same as in §3.3, excepting that two include paths are swaped, what is a very important thing.

4.6 Default paths for a single versioned relocatable MinGW GCC

All paths are exactly the same as in §3.5 (there was only one include path, so we can forgot about the permutation).

The comment about the include path is the same as in §3.6, that is to say “ There are no good candidates for includes ”.

5 Without a build sysroot option

The latter tests in §4 were made using the same path for sysroot and build sysroot. It was interresting to test weither or not the result would be the same whith no build sysroot, providing in this case, build sysroot is supposed to be defaulted to the value of sysroot. So we may expect the result to be the same, but it is not exactly : the two last include search paths are swaped again, thus the order is back to the same as in §3.1.

Although this seems funny at first sight, using a build sysroot with the same value as sysroot or using no build sysroot at all, has an impact on the default include search paths ordering.

For a multi-arch single versioned installation, the sole default include path is the same as for §3 and §4.

All the remaining stuff is the same as the whole of §4.

6 Playing with the local prefix option

Surprizingly, the --with-local-prefix option does not seems to be used (at least, to have any impact) at build time nor at run time. It does not appears in any include search paths at build time, and it does not appears in any default paths at run time.

To check if it is has any effect or not, a test was done, giving the local prefix option, the same value as the sysroot option.

The result is a bit like the as with §5, that is to say that there is a swap of the two last default include search paths, which are in this case, the same as in §4, that is to say the same than the case where both sysroot and build sysroot was the same. This may seems strange : local prefix had not any effects so far, but it has one on the ordering of the default include paths when its value is the same as the one given for sysroot.

A second test was made, giving no local prefix option at all (i.e. there is a lonely sysroot option). The result is exactly the same as above, when the local prefix was assigned to the same value as the sysroot option (the order here is the same as in §4.3).

7 Assigning the arch path to the three sysroot, build sysroot and local prefix

Now back to a context similar to the one of §2. The difference will be that we will use <install-dir>/<arch> as the argument for the three options (no more test1, test2 and test3).

The results of the tests done here was predictable, while it was in the mean time better to ensure about it.

After the tests are done, as you may have guessed, the ming/include path is now expected in <install-dir>/<arch> and includes required during the build are now searched in <install-dir>/<arch>/include and in <install-dir>/<arch>/mingw/include.

The resulting MinGW GCC has the same installation and program paths as in §2 (and all the others up to §6 by the way). The main part of the libs paths is the same, while beeing different at the end of the list. Which is obvious, beceause test1 does not exist any more. The default include paths list is different as well, mainly for the same reason as the one of the default lib paths.

7.1 The default lib paths

From §2 to §6, the default libs paths was:

  1. <reloc-dir>/lib/gcc/<arch>/<version>/
  2. <reloc-dir>/lib/gcc/
  3. <install-dir>/lib/gcc/<arch>/<version>/
  4. /usr/lib/gcc/<arch>/<version>/
  5. <reloc-dir>/<arch>/lib/<arch>/<version>/
  6. <reloc-dir>/<arch>/lib/
  7. <install-dir>/<arch>/lib/<arch>/<version>/
  8. <install-dir>/<arch>/lib/
  9. <reloc-dir>/lib/<arch>/<version>/
  10. <reloc-dir>/lib/
  11. <install-dir>/lib/<arch>/<version>/
  12. <install-dir>/lib/
  13. <reloc-dir>/<arch>/test1/mingw/lib/<arch>/<version>/
  14. <reloc-dir>/<arch>/test1/mingw/lib/

The one resulting from this new options context is now:

  1. <reloc-dir>/lib/gcc/<arch>/<version>/
  2. <reloc-dir>/lib/gcc/
  3. <install-dir>/lib/gcc/<arch>/<version>/
  4. /usr/lib/gcc/<arch>/<version>/
  5. <reloc-dir>/<arch>/lib/<arch>/<version>/
  6. <reloc-dir>/<arch>/lib/
  7. <install-dir>/<arch>/lib/<arch>/<version>/
  8. <install-dir>/<arch>/lib/
  9. <reloc-dir>/lib/<arch>/<version>/
  10. <reloc-dir>/lib/
  11. <install-dir>/lib/<arch>/<version>/
  12. <install-dir>/lib/
  13. <reloc-dir>/<arch>/mingw/lib/<arch>/<version>/
  14. <reloc-dir>/<arch>/mingw/lib/

7.2 Comments on the latter

The difference is in the two last lib paths:

  1. <reloc-dir>/<arch>/mingw/lib/<arch>/<version>/
  2. <reloc-dir>/<arch>/mingw/lib/

This is just that test1 has disappeared, there are not more impact.

For a relocatable installation, we may rely on:

  • <reloc-dir>/lib/gcc/<arch>/<version>/
  • <reloc-dir>/lib/gcc/
  • <reloc-dir>/<arch>/lib/<arch>/<version>/
  • <reloc-dir>/<arch>/lib/
  • <reloc-dir>/lib/<arch>/<version>/
  • <reloc-dir>/lib/
  • <reloc-dir>/<arch>/mingw/lib/<arch>/<version>/
  • <reloc-dir>/<arch>/mingw/lib/

For a single versioned relocatable installation, we may rely on:

  • <reloc-dir>/lib/gcc/
  • <reloc-dir>/<arch>/lib/
  • <reloc-dir>/lib/
  • <reloc-dir>/<arch>/mingw/lib/

7.3 The default include paths

From §2 to §6, the default include paths was:

  1. <reloc-dir>/<arch>/test1<install-dir>/include
  2. <install-dir>/lib/gcc/<arch>/<version>/include
  3. <install-dir>/<arch>/include
  4. <reloc-dir>/<arch>/test1/mingw/include
  5. <reloc-dir>/lib/gcc/<arch>/<version>/include

The one resulting from the this new options context is now:

  1. <reloc-dir>/<arch><install-dir>/include
  2. <install-dir>/lib/gcc/<arch>/<version>/include
  3. <install-dir>/<arch>/include
  4. <reloc-dir>/lib/gcc/<arch>/<version>/include
  5. <reloc-dir>/<arch>/mingw/include

7.4 Comments on the latter

One again, the only difference is that test1 has dissapeared.

Notice that the last two include path, excepting the fact that test1 is not there in the second list, are swaped. The last two elements of the default include paths are indeed easily swaped and the order is very sensitive to the options. No test were made about the swap condition this time (to not to be too much long), but we may guess it is swaped in the same conditions as in §4, §5 and §6.

Notice that the first default include path still shows the same concatenation bug. This bug is indeed very persistant. This concatenation may have sense if the <install-dir> could be a relative path, but it cannot : the configuration script expect --prefix to be assigned with an absolute path.

For a relocatable installation, we may rely on:

  • <reloc-dir>/lib/gcc/<arch>/<version>/include
  • <reloc-dir>/<arch>/mingw/include

For a single versioned relocatable installation, we may rely on: <reloc-dir>/<arch>/mingw/include

Notice that there is still no good canditates for the default include path in the context of a single versioned relocatable installation.

7.5 Parameters received by cc1

No surprise with the parameters received by cc1:

  • -iprefix <reloc-dir>/lib/gcc/<arch>/<version>/
  • -isysroot <reloc-dir>/<arch>

There are still both relocatable, but only -isysroot is not versioned.

8 More on directory structure and possible failures at build time

If one scrupulously check the rules given is this document to predict the effects of its own paths configuration options and although he/she give all the necessary include files for MinGW in the mingw/include directory (a nice choice, indeed), he/she may still face some failures at build time.

8.1 Failure while compiling libSSP

The make script may complains with a:

configure: error: C preprocessor "/lib/cpp" fails sanity check
See `config.log' for more details.
make[1]: *** [configure-target-libssp] Error 1
make[1]: Leaving directory `<build-dir>'
make: *** [all] Error 2

The refered libssp/config.log contained mutliple “failed statements”. The first one was complaining that the file “stdio.h” was not found. This error occured during the following command (given in libssp/configure.log and reformated for the purpose of this document):

-isystem <source-dir>/winsup/mingw/include
-isystem <source-dir>/winsup/w32api/include
-isystem <install-dir>/<arch>/include
-isystem <install-dir>/<arch>/sys-include

What is noticable here, is that <install-dir>/<arch>/mingw/include is not search for includes.

This only appens during the configuration/build of libssp (a library for stack smashing protection). If the creation of this library is disabled by the configuration option --disable-libssp, then the trouble does not express any more.

This seems to be a bug in the pre-build configuration script of libssp. This may be useful to check if weither or not this bug is specific to all versions of MinGW GCC sources or not.

As shown the options given to the command which is in failure, the file “stdio.h” was not found, beceause the directory mingw/include was not searched. But the directory <arch>/include is searched.

So there are two immediat solutions and two alternatives one:

  1. Using <arch>/include for the include files
  2. Using <arch>/include temporarly and then moving its content in mingw/include after “make install” is done.
  3. To put ANSI C include files in <arch>/include and left MinGW specific includes in mingw/include (the include files which cause the failure are all standard ANSI C include files). See later comment.
  4. Do not build libssp (but do not make this choice just due to this bug, as there are workarounds).

If you choose to split include files, moving standard C files in <arch>/include and specific MinGW include files in <arch>/mingw/include, you will have to move all ISO C include files in <arch>/include (see the list later), plus the includes fcntl.h, io.h and all of the sys/*.h (which are not part of ANSI or ISO C) and the _mingw.h as well. The file _mingw.h is referenced by all include files, even ANSI/ISO C include files.

List of ISO files to move into <arch>/include (if you opt for this):

  • assert.h
  • complex.h
  • ctype.h
  • errno.h
  • fenv.h
  • float.h
  • inttypes.h
  • iso646.h
  • limits.h
  • locale.h
  • math.h
  • setjmp.h
  • signal.h
  • stdarg.h
  • stdbool.h
  • stdint.h
  • stddef.h
  • stdio.h
  • stdlib.h
  • string.h
  • tgmath.h (does not exist in MinGW GCC)
  • time.h
  • wchar.h
  • wctype.h

Remember that this is more a bug than a MinGW GCC configuration property ! The remaining of the libssp build process cleanly make reference to mingw/include. Only the pre-build configuration seems to be broken.

Although all of this is about a bug, it is still nice to split include files with ANSI/ISO C files on one side and MinGW include files on an other.

8.2 Failure while compiling libIberty

The trouble during the build of libIberty is the same as the one with libSSP : it does not search in <arch>/mingw/include for includes file and fails to find the file windows.h. Unfortunately, there is not a nice work around here, like the one to separate ANSI/ISO C files in a folder and MinGW files in an other. But there is a moderately nice solution : create an <arch>/sys-include directory and copy all the content of <arch>/mingw/include in this directory. This will work beceause even if we did not specify any sys-include path in the configuration options, the build of libIberty for MinGW GCC will anyway look in <arch>/sys-include.

This sys-include directory will have to be deleted after make install has been run.

9 Work around the lack of a goog candidate for default include path

As seen before, in some circumstances, the set of paths we may rely on, depending on requirements, may left us with a single default include path which will only search for include files in <reloc-dir>/<arch>/mingw/include. Adding a default path to <reloc-dir>/<arch>/include would be nice there, as well as an include path pointing to <reloc-dir>/include, for plateforme independant includes (there are a few exemples in C, but it is much more common with portable langage like Ada).

The best way to do so, for any one who want to avoid invokation-time parameters and make it working like a default search path, is to update your specs file. If you don't have any specs file, you may create an initial one before you may expect to modify one. Do so with the command “gcc -dumpspecs >specs”. You will then have to move the specs file in one of your library search paths. The most common default location for the specs file is <reloc-dir>/lib/gcc/<arch>/<version>, but believe me, <reloc-dir>/<arch>/<lib> is also a very nice idea. Do not forgot to ensure the path is in you libraries search path (if there are any doubts, run a “gcc -v” to be sure).

The idea is to add two “-idirafter” options to the default CPP invokation parameters. This option fulfill all what we need : it works like the well known “-I” option, with the difference that it will add the path in the system include directory set. This is exactly what we want.

For more information about this option, see GCC Manual: Options Controlling the Preprocessor.

So we will have to add an “-idirafter” option for our <reloc-dir>/<arch>/include path and another one, after (it is important to put it after), for our <reloc-dir>/include path.

For the <reloc-dir>/include we can use <reloc-dir>/<arch>/../include

All remaining needs so far, is thus a way to have the <reloc-dir>/<arch> string.

Depending on the version of (MinGW) GCC you've build, there are two different options. From GCC 4.3.3, new improvement were added in the way pass parameters to the GCC's command line, which will help us. But for GCC with prior version number, we will need another trick.

9.1 Workaround for GCC equal or greater than 4.3.3

Let start with what's new as of GCC 4.3.3. It adds the capabilities to pass path parameters as paths relative to the actual isysroot, using the “=” sign as a prefix of the path. Let me explain with an exemple: the path “=/abc” would turn into “/test/abc” providing that your isysroot is “/test”.

So we just need to have a GCC which was configured with <install-dir>/<arch> as the sysroot. Fortunately, when the sysroot is a subdirectory of the installation directory, GCC will see it as a relative path, so that the sysroot will automatically evaluated from the actual location of GCC. Thus, sysroot will be <reloc-dir>/<arch>, what ever will be <reloc-dir>.

To update your specs file with GCC 4.3.3 or above, you will have to search for the “*cpp:”, then to append the two options to the line just below.

You will have something like:

%{posix:-D_POSIX_SOURCE} %{mthreads:-D_MT} -idirafter =/include -idirafter =/../include

... and voilà :)

You will have to apply the exact same modification for all of your specs file for each of you targets.

One more step forward to the core default stuff: to achieve a real default effect, we may also modify the builting specs source for GCC, before we build it, with a modification of the file <src-dir>/gcc/cp/lang-specs.h . This way, it would be a real built-in specs.

9.2 Workaround for GCC lower than 4.3.3

Unfortunatly, an attempt to apply the latter solution with a GCC whose version is less than 4.3.3, will turn into an error : these versions of GCC do not know about this new meaning of “=” when it occurs as a path prefix, as you may check in GCC 4.2.4 Preprocessor-Options. Facing an attempt to use something like “=/include”, GCC will simply complains that “=/include” does not exist.

Things gonna be less nice, beceause this will not be relocatable. But we may at least try to make things as simple as possible. The modification to apply to the specs file will be very similar to the latter one, with the difference that we will need one more thing, to workaround the lack of beeing able to express paths relatively to the actual sysroot. We may also not be able to make it a default built-in specs, beaceause as you will see later, we will need an hard coded path string.

Juste like explained before, you may locate your specs file or create an initial one. Then you will have to add two lines at the begening of the specs file :


Do not forget to add an empty line juste after !

These two lines will act as a convenient variable we will use later.

As you see, <arch> appears in the text. This means you will have to modifiy all the specs files for each of your targets specifically. And as the <reloc-dir> appears in the string, this means you will have as well to update this whenever you move your GCC environnement installation directory.

Now locate the text “*cpp:”, then go to the line below and append the string
“ %(sysroot)/include -idirafter %(sysroot)/../include”

Do not forget to put a space before.

You should have someting like

%{posix:-D_POSIX_SOURCE} %{mthreads:-D_MT} -idirafter %(sysroot)/include -idirafter %(sysroot)/../include

The latter modification will be the same for all of your specs files of each of your targets (arch). The sole thing which will differ for each of your target, will be the path we've added at the begining of the specs file. If you do a copy past, take care of the <arch> part !

You will have to update these paths whenever you move your installation directory, as it is obviously not relocatable (hard coded absolute paths).

There are no way to make it a built in specs in MinGW GCC <= 4.3.3 (as explained before).


  • TODO: wait for reader suggestions :p


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