(gccinstall.info.gz) Installing GCC
Now that GCC is configured, you are ready to build the compiler and
Some commands executed when making the compiler may fail (return a
nonzero status) and be ignored by `make'. These failures, which are
often due to files that were not found, are expected, and can safely be
It is normal to have compiler warnings when compiling certain files.
Unless you are a GCC developer, you can generally ignore these warnings
unless they cause compilation to fail. Developers should attempt to fix
any warnings encountered, however they can temporarily continue past
warnings-as-errors by specifying the configure flag `--disable-werror'.
On certain old systems, defining certain environment variables such
as `CC' can interfere with the functioning of `make'.
If you encounter seemingly strange errors when trying to build the
compiler in a directory other than the source directory, it could be
because you have previously configured the compiler in the source
directory. Make sure you have done all the necessary preparations.
If you build GCC on a BSD system using a directory stored in an old
System V file system, problems may occur in running `fixincludes' if the
System V file system doesn't support symbolic links. These problems
result in a failure to fix the declaration of `size_t' in
`sys/types.h'. If you find that `size_t' is a signed type and that
type mismatches occur, this could be the cause.
The solution is not to use such a directory for building GCC.
Similarly, when building from SVN or snapshots, or if you modify
`*.l' files, you need the Flex lexical analyzer generator installed.
If you do not modify `*.l' files, releases contain the Flex-generated
files and you do not need Flex installed to build them. There is still
one Flex-based lexical analyzer (part of the build machinery, not of
GCC itself) that is used even if you only build the C front end.
When building from SVN or snapshots, or if you modify Texinfo
documentation, you need version 4.7 or later of Texinfo installed if you
want Info documentation to be regenerated. Releases contain Info
documentation pre-built for the unmodified documentation in the release.
5.1 Building a native compiler
For a native build, the default configuration is to perform a 3-stage
bootstrap of the compiler when `make' is invoked. This will build the
entire GCC system and ensure that it compiles itself correctly. It can
be disabled with the `--disable-bootstrap' parameter to `configure',
but bootstrapping is suggested because the compiler will be tested more
completely and could also have better performance.
The bootstrapping process will complete the following steps:
* Build tools necessary to build the compiler.
* Perform a 3-stage bootstrap of the compiler. This includes
building three times the target tools for use by the compiler such
as binutils (bfd, binutils, gas, gprof, ld, and opcodes) if they
have been individually linked or moved into the top level GCC
source tree before configuring.
* Perform a comparison test of the stage2 and stage3 compilers.
* Build runtime libraries using the stage3 compiler from the
If you are short on disk space you might consider `make
bootstrap-lean' instead. The sequence of compilation is the same
described above, but object files from the stage1 and stage2 of the
3-stage bootstrap of the compiler are deleted as soon as they are no
If you wish to use non-default GCC flags when compiling the stage2
and stage3 compilers, set `BOOT_CFLAGS' on the command line when doing
`make'. For example, if you want to save additional space during the
bootstrap and in the final installation as well, you can build the
compiler binaries without debugging information as in the following
example. This will save roughly 40% of disk space both for the
bootstrap and the final installation. (Libraries will still contain
make BOOT_CFLAGS='-O' bootstrap
You can place non-default optimization flags into `BOOT_CFLAGS'; they
are less well tested here than the default of `-g -O2', but should
still work. In a few cases, you may find that you need to specify
special flags such as `-msoft-float' here to complete the bootstrap; or,
if the native compiler miscompiles the stage1 compiler, you may need to
work around this, by choosing `BOOT_CFLAGS' to avoid the parts of the
stage1 compiler that were miscompiled, or by using `make bootstrap4' to
increase the number of stages of bootstrap.
`BOOT_CFLAGS' does not apply to bootstrapped target libraries.
Since these are always compiled with the compiler currently being
bootstrapped, you can use `CFLAGS_FOR_TARGET' to modify their
compilation flags, as for non-bootstrapped target libraries. Again, if
the native compiler miscompiles the stage1 compiler, you may need to
work around this by avoiding non-working parts of the stage1 compiler.
Use `STAGE1_TFLAGS' to this end.
If you used the flag `--enable-languages=...' to restrict the
compilers to be built, only those you've actually enabled will be
built. This will of course only build those runtime libraries, for
which the particular compiler has been built. Please note, that
re-defining `LANGUAGES' when calling `make' *does not* work anymore!
If the comparison of stage2 and stage3 fails, this normally indicates
that the stage2 compiler has compiled GCC incorrectly, and is therefore
a potentially serious bug which you should investigate and report. (On
a few systems, meaningful comparison of object files is impossible; they
always appear "different". If you encounter this problem, you will
need to disable comparison in the `Makefile'.)
If you do not want to bootstrap your compiler, you can configure with
`--disable-bootstrap'. In particular cases, you may want to bootstrap
your compiler even if the target system is not the same as the one you
are building on: for example, you could build a
`powerpc-unknown-linux-gnu' toolchain on a
`powerpc64-unknown-linux-gnu' host. In this case, pass
`--enable-bootstrap' to the configure script.
`BUILD_CONFIG' can be used to bring in additional customization to
the build. It can be set to a whitespace-separated list of names. For
each such `NAME', top-level `config/`NAME'.mk' will be included by the
top-level `Makefile', bringing in any settings it contains. The
default `BUILD_CONFIG' can be set using the configure option
`--with-build-config=`NAME'...'. Some examples of supported build
Removes any `-O'-started option from `BOOT_CFLAGS', and adds `-O1'
to it. `BUILD_CONFIG=bootstrap-O1' is equivalent to
Analogous to `bootstrap-O1'.
Verifies that the compiler generates the same executable code,
whether or not it is asked to emit debug information. To this
end, this option builds stage2 host programs without debug
information, and uses `contrib/compare-debug' to compare them with
the stripped stage3 object files. If `BOOT_CFLAGS' is overridden
so as to not enable debug information, stage2 will have it, and
stage3 won't. This option is enabled by default when GCC
bootstrapping is enabled, if `strip' can turn object files
compiled with and without debug info into identical object files.
In addition to better test coverage, this option makes default
bootstraps faster and leaner.
Rather than comparing stripped object files, as in
`bootstrap-debug', this option saves internal compiler dumps
during stage2 and stage3 and compares them as well, which helps
catch additional potential problems, but at a great cost in terms
of disk space. It can be specified in addition to
This option saves disk space compared with `bootstrap-debug-big',
but at the expense of some recompilation. Instead of saving the
dumps of stage2 and stage3 until the final compare, it uses
`-fcompare-debug' to generate, compare and remove the dumps during
stage3, repeating the compilation that already took place in
stage2, whose dumps were not saved.
This option tests executable code invariance over debug information
generation on target libraries, just like `bootstrap-debug-lean'
tests it on host programs. It builds stage3 libraries with
`-fcompare-debug', and it can be used along with any of the
`bootstrap-debug' options above.
There aren't `-lean' or `-big' counterparts to this option because
most libraries are only build in stage3, so bootstrap compares
would not get significant coverage. Moreover, the few libraries
built in stage2 are used in stage3 host programs, so we wouldn't
want to compile stage2 libraries with different options for
Arranges for error messages to be issued if the compiler built on
any stage is run without the option `-fcompare-debug'. This is
useful to verify the full `-fcompare-debug' testing coverage. It
must be used along with `bootstrap-debug-lean' and
Arranges for the run time of each program started by the GCC
driver, built in any stage, to be logged to `time.log', in the top
level of the build tree.
5.2 Building a cross compiler
When building a cross compiler, it is not generally possible to do a
3-stage bootstrap of the compiler. This makes for an interesting
problem as parts of GCC can only be built with GCC.
To build a cross compiler, we first recommend building and
installing a native compiler. You can then use the native GCC compiler
to build the cross compiler. The installed native compiler needs to be
GCC version 2.95 or later.
If the cross compiler is to be built with support for the Java
programming language and the ability to compile .java source files is
desired, the installed native compiler used to build the cross compiler
needs to be the same GCC version as the cross compiler. In addition
the cross compiler needs to be configured with `--with-ecj-jar=...'.
Assuming you have already installed a native copy of GCC and
configured your cross compiler, issue the command `make', which
performs the following steps:
* Build host tools necessary to build the compiler.
* Build target tools for use by the compiler such as binutils (bfd,
binutils, gas, gprof, ld, and opcodes) if they have been
individually linked or moved into the top level GCC source tree
* Build the compiler (single stage only).
* Build runtime libraries using the compiler from the previous step.
Note that if an error occurs in any step the make process will exit.
If you are not building GNU binutils in the same source tree as GCC,
you will need a cross-assembler and cross-linker installed before
configuring GCC. Put them in the directory `PREFIX/TARGET/bin'. Here
is a table of the tools you should put in this directory:
This should be the cross-assembler.
This should be the cross-linker.
This should be the cross-archiver: a program which can manipulate
archive files (linker libraries) in the target machine's format.
This should be a program to construct a symbol table in an archive
The installation of GCC will find these programs in that directory,
and copy or link them to the proper place to for the cross-compiler to
find them when run later.
The easiest way to provide these files is to build the Binutils
package. Configure it with the same `--host' and `--target' options
that you use for configuring GCC, then build and install them. They
install their executables automatically into the proper directory.
Alas, they do not support all the targets that GCC supports.
If you are not building a C library in the same source tree as GCC,
you should also provide the target libraries and headers before
configuring GCC, specifying the directories with `--with-sysroot' or
`--with-headers' and `--with-libs'. Many targets also require "start
files" such as `crt0.o' and `crtn.o' which are linked into each
executable. There may be several alternatives for `crt0.o', for use
with profiling or other compilation options. Check your target's
definition of `STARTFILE_SPEC' to find out what start files it uses.
5.3 Building in parallel
GNU Make 3.79 and above, which is necessary to build GCC, support
building in parallel. To activate this, you can use `make -j 2'
instead of `make'. You can also specify a bigger number, and in most
cases using a value greater than the number of processors in your
machine will result in fewer and shorter I/O latency hits, thus
improving overall throughput; this is especially true for slow drives
and network filesystems.
5.4 Building the Ada compiler
In order to build GNAT, the Ada compiler, you need a working GNAT
compiler (GCC version 3.4 or later). This includes GNAT tools such as
`gnatmake' and `gnatlink', since the Ada front end is written in Ada and
uses some GNAT-specific extensions.
In order to build a cross compiler, it is suggested to install the
new compiler as native first, and then use it to build the cross
`configure' does not test whether the GNAT installation works and
has a sufficiently recent version; if too old a GNAT version is
installed, the build will fail unless `--enable-languages' is used to
disable building the Ada front end.
`ADA_INCLUDE_PATH' and `ADA_OBJECT_PATH' environment variables must
not be set when building the Ada compiler, the Ada tools, or the Ada
runtime libraries. You can check that your build environment is clean
by verifying that `gnatls -v' lists only one explicit path in each
5.5 Building with profile feedback
It is possible to use profile feedback to optimize the compiler itself.
This should result in a faster compiler binary. Experiments done on
x86 using gcc 3.3 showed approximately 7 percent speedup on compiling C
programs. To bootstrap the compiler with profile feedback, use `make
When `make profiledbootstrap' is run, it will first build a `stage1'
compiler. This compiler is used to build a `stageprofile' compiler
instrumented to collect execution counts of instruction and branch
probabilities. Then runtime libraries are compiled with profile
collected. Finally a `stagefeedback' compiler is built using the
Unlike standard bootstrap, several additional restrictions apply.
The compiler used to build `stage1' needs to support a 64-bit integral
type. It is recommended to only use GCC for this. Also parallel make
is currently not supported since collisions in profile collecting may
(gccinstall.info.gz) Installing GCC
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