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GCC Frequently Asked Questions
|
GCC Frequently Asked Questions
|
|
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The latest version of this document is always available at
|
The latest version of this document is always available at
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[1]http://gcc.gnu.org/faq.html.
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[1]http://gcc.gnu.org/faq.html.
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|
This FAQ tries to answer specific questions concerning GCC. For general
|
This FAQ tries to answer specific questions concerning GCC. For general
|
information regarding C, C++, resp. Fortran please check the [2]comp.lang.c
|
information regarding C, C++, resp. Fortran please check the [2]comp.lang.c
|
FAQ, [3]comp.std.c++ FAQ, and the [4]Fortran Information page.
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FAQ, [3]comp.std.c++ FAQ, and the [4]Fortran Information page.
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Other GCC-related FAQs: [5]libstdc++-v3, and [6]GCJ.
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Other GCC-related FAQs: [5]libstdc++-v3, and [6]GCJ.
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_________________________________________________________________
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_________________________________________________________________
|
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Questions
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Questions
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|
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1. [7]General information
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1. [7]General information
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1. [8]How do I get a bug fixed or a feature added?
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1. [8]How do I get a bug fixed or a feature added?
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2. [9]Does GCC work on my platform?
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2. [9]Does GCC work on my platform?
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2. [10]Installation
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2. [10]Installation
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1. [11]How to install multiple versions of GCC
|
1. [11]How to install multiple versions of GCC
|
2. [12]Dynamic linker is unable to find GCC libraries
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2. [12]Dynamic linker is unable to find GCC libraries
|
3. [13]libstdc++/libio tests fail badly with --enable-shared
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3. [13]libstdc++/libio tests fail badly with --enable-shared
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4. [14]GCC can not find GNU as/GNU ld
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4. [14]GCC can not find GNU as/GNU ld
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5. [15]cpp: Usage:... Error
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5. [15]cpp: Usage:... Error
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6. [16]Optimizing the compiler itself
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6. [16]Optimizing the compiler itself
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7. [17]Why does libiconv get linked into jc1 on Solaris?
|
7. [17]Why does libiconv get linked into jc1 on Solaris?
|
3. [18]Testsuite problems
|
3. [18]Testsuite problems
|
1. [19]How do I pass flags like -fnew-abi to the testsuite?
|
1. [19]How do I pass flags like -fnew-abi to the testsuite?
|
2. [20]How can I run the test suite with multiple options?
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2. [20]How can I run the test suite with multiple options?
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4. [21]Miscellaneous
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4. [21]Miscellaneous
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1. [22]Friend Templates
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1. [22]Friend Templates
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2. [23]dynamic_cast, throw, typeid don't work with shared libraries
|
2. [23]dynamic_cast, throw, typeid don't work with shared libraries
|
3. [24]Why do I need autoconf, bison, xgettext, automake, etc?
|
3. [24]Why do I need autoconf, bison, xgettext, automake, etc?
|
4. [25]Why can't I build a shared library?
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4. [25]Why can't I build a shared library?
|
5. [26]When building C++, the linker says my constructors, destructors
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5. [26]When building C++, the linker says my constructors, destructors
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or virtual tables are undefined, but I defined them
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or virtual tables are undefined, but I defined them
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_________________________________________________________________
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_________________________________________________________________
|
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General information
|
General information
|
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How do I get a bug fixed or a feature added?
|
How do I get a bug fixed or a feature added?
|
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|
There are lots of ways to get something fixed. The list below may be
|
There are lots of ways to get something fixed. The list below may be
|
incomplete, but it covers many of the common cases. These are listed roughly
|
incomplete, but it covers many of the common cases. These are listed roughly
|
in order of decreasing difficulty for the average GCC user, meaning someone
|
in order of decreasing difficulty for the average GCC user, meaning someone
|
who is not skilled in the internals of GCC, and where difficulty is measured
|
who is not skilled in the internals of GCC, and where difficulty is measured
|
in terms of the time required to fix the bug. No alternative is better than
|
in terms of the time required to fix the bug. No alternative is better than
|
any other; each has its benefits and disadvantages.
|
any other; each has its benefits and disadvantages.
|
* Fix it yourself. This alternative will probably bring results, if you
|
* Fix it yourself. This alternative will probably bring results, if you
|
work hard enough, but will probably take a lot of time, and, depending
|
work hard enough, but will probably take a lot of time, and, depending
|
on the quality of your work and the perceived benefits of your changes,
|
on the quality of your work and the perceived benefits of your changes,
|
your code may or may not ever make it into an official release of GCC.
|
your code may or may not ever make it into an official release of GCC.
|
* [27]Report the problem to the GCC bug tracking system and hope that
|
* [27]Report the problem to the GCC bug tracking system and hope that
|
someone will be kind enough to fix it for you. While this is certainly
|
someone will be kind enough to fix it for you. While this is certainly
|
possible, and often happens, there is no guarantee that it will. You
|
possible, and often happens, there is no guarantee that it will. You
|
should not expect the same response from this method that you would see
|
should not expect the same response from this method that you would see
|
from a commercial support organization since the people who read GCC bug
|
from a commercial support organization since the people who read GCC bug
|
reports, if they choose to help you, will be volunteering their time.
|
reports, if they choose to help you, will be volunteering their time.
|
* Hire someone to fix it for you. There are various companies and
|
* Hire someone to fix it for you. There are various companies and
|
individuals providing support for GCC. This alternative costs money, but
|
individuals providing support for GCC. This alternative costs money, but
|
is relatively likely to get results.
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is relatively likely to get results.
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_________________________________________________________________
|
_________________________________________________________________
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Does GCC work on my platform?
|
Does GCC work on my platform?
|
|
|
The host/target specific installation notes for GCC include information
|
The host/target specific installation notes for GCC include information
|
about known problems with installing or using GCC on particular platforms.
|
about known problems with installing or using GCC on particular platforms.
|
These are included in the sources for a release in INSTALL/specific.html,
|
These are included in the sources for a release in INSTALL/specific.html,
|
and the [28]latest version is always available at the GCC web site. Reports
|
and the [28]latest version is always available at the GCC web site. Reports
|
of [29]successful builds for several versions of GCC are also available at
|
of [29]successful builds for several versions of GCC are also available at
|
the web site.
|
the web site.
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_________________________________________________________________
|
_________________________________________________________________
|
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Installation
|
Installation
|
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How to install multiple versions of GCC
|
How to install multiple versions of GCC
|
|
|
It may be desirable to install multiple versions of the compiler on the same
|
It may be desirable to install multiple versions of the compiler on the same
|
system. This can be done by using different prefix paths at configure time
|
system. This can be done by using different prefix paths at configure time
|
and a few symlinks.
|
and a few symlinks.
|
|
|
Basically, configure the two compilers with different --prefix options, then
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Basically, configure the two compilers with different --prefix options, then
|
build and install each compiler. Assume you want "gcc" to be the latest
|
build and install each compiler. Assume you want "gcc" to be the latest
|
compiler and available in /usr/local/bin; also assume that you want "gcc2"
|
compiler and available in /usr/local/bin; also assume that you want "gcc2"
|
to be the older gcc2 compiler and also available in /usr/local/bin.
|
to be the older gcc2 compiler and also available in /usr/local/bin.
|
|
|
The easiest way to do this is to configure the new GCC with
|
The easiest way to do this is to configure the new GCC with
|
--prefix=/usr/local/gcc and the older gcc2 with --prefix=/usr/local/gcc2.
|
--prefix=/usr/local/gcc and the older gcc2 with --prefix=/usr/local/gcc2.
|
Build and install both compilers. Then make a symlink from
|
Build and install both compilers. Then make a symlink from
|
/usr/local/bin/gcc to /usr/local/gcc/bin/gcc and from /usr/local/bin/gcc2 to
|
/usr/local/bin/gcc to /usr/local/gcc/bin/gcc and from /usr/local/bin/gcc2 to
|
/usr/local/gcc2/bin/gcc. Create similar links for the "g++", "c++" and "g77"
|
/usr/local/gcc2/bin/gcc. Create similar links for the "g++", "c++" and "g77"
|
compiler drivers.
|
compiler drivers.
|
|
|
An alternative to using symlinks is to configure with a
|
An alternative to using symlinks is to configure with a
|
--program-transform-name option. This option specifies a sed command to
|
--program-transform-name option. This option specifies a sed command to
|
process installed program names with. Using it you can, for instance, have
|
process installed program names with. Using it you can, for instance, have
|
all the new GCC programs installed as "new-gcc" and the like. You will still
|
all the new GCC programs installed as "new-gcc" and the like. You will still
|
have to specify different --prefix options for new GCC and old GCC, because
|
have to specify different --prefix options for new GCC and old GCC, because
|
it is only the executable program names that are transformed. The difference
|
it is only the executable program names that are transformed. The difference
|
is that you (as administrator) do not have to set up symlinks, but must
|
is that you (as administrator) do not have to set up symlinks, but must
|
specify additional directories in your (as a user) PATH. A complication with
|
specify additional directories in your (as a user) PATH. A complication with
|
--program-transform-name is that the sed command invariably contains
|
--program-transform-name is that the sed command invariably contains
|
characters significant to the shell, and these have to be escaped correctly,
|
characters significant to the shell, and these have to be escaped correctly,
|
also it is not possible to use "^" or "$" in the command. Here is the option
|
also it is not possible to use "^" or "$" in the command. Here is the option
|
to prefix "new-" to the new GCC installed programs:
|
to prefix "new-" to the new GCC installed programs:
|
|
|
--program-transform-name='s,\\\\(.*\\\\),new-\\\\1,'
|
--program-transform-name='s,\\\\(.*\\\\),new-\\\\1,'
|
|
|
With the above --prefix option, that will install the new GCC programs into
|
With the above --prefix option, that will install the new GCC programs into
|
/usr/local/gcc/bin with names prefixed by "new-". You can use
|
/usr/local/gcc/bin with names prefixed by "new-". You can use
|
--program-transform-name if you have multiple versions of GCC, and wish to
|
--program-transform-name if you have multiple versions of GCC, and wish to
|
be sure about which version you are invoking.
|
be sure about which version you are invoking.
|
|
|
If you use --prefix, GCC may have difficulty locating a GNU assembler or
|
If you use --prefix, GCC may have difficulty locating a GNU assembler or
|
linker on your system, [30]GCC can not find GNU as/GNU ld explains how to
|
linker on your system, [30]GCC can not find GNU as/GNU ld explains how to
|
deal with this.
|
deal with this.
|
|
|
Another option that may be easier is to use the --program-prefix= or
|
Another option that may be easier is to use the --program-prefix= or
|
--program-suffix= options to configure. So if you're installing GCC 2.95.2
|
--program-suffix= options to configure. So if you're installing GCC 2.95.2
|
and don't want to disturb the current version of GCC in /usr/local/bin/, you
|
and don't want to disturb the current version of GCC in /usr/local/bin/, you
|
could do
|
could do
|
|
|
configure --program-suffix=-2.95.2
|
configure --program-suffix=-2.95.2
|
|
|
This should result in GCC being installed as /usr/local/bin/gcc-2.95.2
|
This should result in GCC being installed as /usr/local/bin/gcc-2.95.2
|
instead of /usr/local/bin/gcc.
|
instead of /usr/local/bin/gcc.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
Dynamic linker is unable to find GCC libraries
|
Dynamic linker is unable to find GCC libraries
|
|
|
This problem manifests itself by programs not finding shared libraries they
|
This problem manifests itself by programs not finding shared libraries they
|
depend on when the programs are started. Note this problem often manifests
|
depend on when the programs are started. Note this problem often manifests
|
itself with failures in the libio/libstdc++ tests after configuring with
|
itself with failures in the libio/libstdc++ tests after configuring with
|
--enable-shared and building GCC.
|
--enable-shared and building GCC.
|
|
|
GCC does not specify a runpath so that the dynamic linker can find dynamic
|
GCC does not specify a runpath so that the dynamic linker can find dynamic
|
libraries at runtime.
|
libraries at runtime.
|
|
|
The short explanation is that if you always pass a -R option to the linker,
|
The short explanation is that if you always pass a -R option to the linker,
|
then your programs become dependent on directories which may be NFS mounted,
|
then your programs become dependent on directories which may be NFS mounted,
|
and programs may hang unnecessarily when an NFS server goes down.
|
and programs may hang unnecessarily when an NFS server goes down.
|
|
|
The problem is not programs that do require the directories; those programs
|
The problem is not programs that do require the directories; those programs
|
are going to hang no matter what you do. The problem is programs that do not
|
are going to hang no matter what you do. The problem is programs that do not
|
require the directories.
|
require the directories.
|
|
|
SunOS effectively always passed a -R option for every -L option; this was a
|
SunOS effectively always passed a -R option for every -L option; this was a
|
bad idea, and so it was removed for Solaris. We should not recreate it.
|
bad idea, and so it was removed for Solaris. We should not recreate it.
|
|
|
However, if you feel you really need such an option to be passed
|
However, if you feel you really need such an option to be passed
|
automatically to the linker, you may add it to the GCC specs file. This file
|
automatically to the linker, you may add it to the GCC specs file. This file
|
can be found in the same directory that contains cc1 (run gcc
|
can be found in the same directory that contains cc1 (run gcc
|
-print-prog-name=cc1 to find it). You may add linker flags such as -R or
|
-print-prog-name=cc1 to find it). You may add linker flags such as -R or
|
-rpath, depending on platform and linker, to the *link or *lib specs.
|
-rpath, depending on platform and linker, to the *link or *lib specs.
|
|
|
Another alternative is to install a wrapper script around gcc, g++ or ld
|
Another alternative is to install a wrapper script around gcc, g++ or ld
|
that adds the appropriate directory to the environment variable LD_RUN_PATH
|
that adds the appropriate directory to the environment variable LD_RUN_PATH
|
or equivalent (again, it's platform-dependent).
|
or equivalent (again, it's platform-dependent).
|
|
|
Yet another option, that works on a few platforms, is to hard-code the full
|
Yet another option, that works on a few platforms, is to hard-code the full
|
pathname of the library into its soname. This can only be accomplished by
|
pathname of the library into its soname. This can only be accomplished by
|
modifying the appropriate .ml file within libstdc++/config (and also
|
modifying the appropriate .ml file within libstdc++/config (and also
|
libg++/config, if you are building libg++), so that $(libdir)/ appears just
|
libg++/config, if you are building libg++), so that $(libdir)/ appears just
|
before the library name in -soname or -h options.
|
before the library name in -soname or -h options.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
GCC can not find GNU as/GNU ld
|
GCC can not find GNU as/GNU ld
|
|
|
GCC searches the PATH for an assembler and a loader, but it only does so
|
GCC searches the PATH for an assembler and a loader, but it only does so
|
after searching a directory list hard-coded in the GCC executables. Since,
|
after searching a directory list hard-coded in the GCC executables. Since,
|
on most platforms, the hard-coded list includes directories in which the
|
on most platforms, the hard-coded list includes directories in which the
|
system assembler and loader can be found, you may have to take one of the
|
system assembler and loader can be found, you may have to take one of the
|
following actions to arrange that GCC uses the GNU versions of those
|
following actions to arrange that GCC uses the GNU versions of those
|
programs.
|
programs.
|
|
|
To ensure that GCC finds the GNU assembler (the GNU loader), which are
|
To ensure that GCC finds the GNU assembler (the GNU loader), which are
|
required by [31]some configurations, you should configure these with the
|
required by [31]some configurations, you should configure these with the
|
same --prefix option as you used for GCC. Then build & install GNU as (GNU
|
same --prefix option as you used for GCC. Then build & install GNU as (GNU
|
ld) and proceed with building GCC.
|
ld) and proceed with building GCC.
|
|
|
Another alternative is to create links to GNU as and ld in any of the
|
Another alternative is to create links to GNU as and ld in any of the
|
directories printed by the command `gcc -print-search-dirs | grep
|
directories printed by the command `gcc -print-search-dirs | grep
|
'^programs:''. The link to `ld' should be named `real-ld' if `ld' already
|
'^programs:''. The link to `ld' should be named `real-ld' if `ld' already
|
exists. If such links do not exist while you're compiling GCC, you may have
|
exists. If such links do not exist while you're compiling GCC, you may have
|
to create them in the build directories too, within the gcc directory and in
|
to create them in the build directories too, within the gcc directory and in
|
all the gcc/stage* subdirectories.
|
all the gcc/stage* subdirectories.
|
|
|
GCC 2.95 allows you to specify the full pathname of the assembler and the
|
GCC 2.95 allows you to specify the full pathname of the assembler and the
|
linker to use. The configure flags are `--with-as=/path/to/as' and
|
linker to use. The configure flags are `--with-as=/path/to/as' and
|
`--with-ld=/path/to/ld'. GCC will try to use these pathnames before looking
|
`--with-ld=/path/to/ld'. GCC will try to use these pathnames before looking
|
for `as' or `(real-)ld' in the standard search dirs. If, at configure-time,
|
for `as' or `(real-)ld' in the standard search dirs. If, at configure-time,
|
the specified programs are found to be GNU utilities, `--with-gnu-as' and
|
the specified programs are found to be GNU utilities, `--with-gnu-as' and
|
`--with-gnu-ld' need not be used; these flags will be auto-detected. One
|
`--with-gnu-ld' need not be used; these flags will be auto-detected. One
|
drawback of this option is that it won't allow you to override the search
|
drawback of this option is that it won't allow you to override the search
|
path for assembler and linker with command-line options -B/path/ if the
|
path for assembler and linker with command-line options -B/path/ if the
|
specified filenames exist.
|
specified filenames exist.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
cpp: Usage:... Error
|
cpp: Usage:... Error
|
|
|
If you get an error like this when building GCC (particularly when building
|
If you get an error like this when building GCC (particularly when building
|
__mulsi3), then you likely have a problem with your environment variables.
|
__mulsi3), then you likely have a problem with your environment variables.
|
cpp: Usage: /usr/lib/gcc-lib/i586-unknown-linux-gnulibc1/2.7.2.3/cpp
|
cpp: Usage: /usr/lib/gcc-lib/i586-unknown-linux-gnulibc1/2.7.2.3/cpp
|
[switches] input output
|
[switches] input output
|
|
|
First look for an explicit '.' in either LIBRARY_PATH or GCC_EXEC_PREFIX
|
First look for an explicit '.' in either LIBRARY_PATH or GCC_EXEC_PREFIX
|
from your environment. If you do not find an explicit '.', look for an empty
|
from your environment. If you do not find an explicit '.', look for an empty
|
pathname in those variables. Note that ':' at either the start or end of
|
pathname in those variables. Note that ':' at either the start or end of
|
these variables is an implicit '.' and will cause problems.
|
these variables is an implicit '.' and will cause problems.
|
|
|
Also note '::' in these paths will also cause similar problems.
|
Also note '::' in these paths will also cause similar problems.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
Optimizing the compiler itself
|
Optimizing the compiler itself
|
|
|
If you want to test a particular optimization option, it's useful to try
|
If you want to test a particular optimization option, it's useful to try
|
bootstrapping the compiler with that option turned on. For example, to test
|
bootstrapping the compiler with that option turned on. For example, to test
|
the -fssa option, you could bootstrap like this:
|
the -fssa option, you could bootstrap like this:
|
make BOOT_CFLAGS="-O2 -fssa" bootstrap
|
make BOOT_CFLAGS="-O2 -fssa" bootstrap
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
Why does libiconv get linked into jc1 on Solaris?
|
Why does libiconv get linked into jc1 on Solaris?
|
|
|
The Java front end requires iconv. If the compiler used to bootstrap GCC
|
The Java front end requires iconv. If the compiler used to bootstrap GCC
|
finds libiconv (because the GNU version of libiconv has been installed in
|
finds libiconv (because the GNU version of libiconv has been installed in
|
the same prefix as the bootstrap compiler), but the newly built GCC does not
|
the same prefix as the bootstrap compiler), but the newly built GCC does not
|
find the library (because it will be installed with a different prefix),
|
find the library (because it will be installed with a different prefix),
|
then a link-time error will occur when building jc1. This problem does not
|
then a link-time error will occur when building jc1. This problem does not
|
show up so often on platforms that have libiconv in a default location (like
|
show up so often on platforms that have libiconv in a default location (like
|
/usr/lib) because then both compilers can find a library named libiconv,
|
/usr/lib) because then both compilers can find a library named libiconv,
|
even though it is a different library.
|
even though it is a different library.
|
|
|
Using --disable-nls at configure-time does not prevent this problem because
|
Using --disable-nls at configure-time does not prevent this problem because
|
jc1 uses iconv even in that case. Solutions include temporarily removing the
|
jc1 uses iconv even in that case. Solutions include temporarily removing the
|
GNU libiconv, copying it to a default location such as /usr/lib/, and using
|
GNU libiconv, copying it to a default location such as /usr/lib/, and using
|
--enable-languages at configure-time to disable Java.
|
--enable-languages at configure-time to disable Java.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
Testsuite problems
|
Testsuite problems
|
|
|
How do I pass flags like -fnew-abi to the testsuite?
|
How do I pass flags like -fnew-abi to the testsuite?
|
|
|
If you invoke runtest directly, you can use the --tool_opts option, e.g:
|
If you invoke runtest directly, you can use the --tool_opts option, e.g:
|
runtest --tool_opts "-fnew-abi -fno-honor-std"
|
runtest --tool_opts "-fnew-abi -fno-honor-std"
|
|
|
Or, if you use make check you can use the make variable RUNTESTFLAGS, e.g:
|
Or, if you use make check you can use the make variable RUNTESTFLAGS, e.g:
|
make RUNTESTFLAGS="--tool_opts '-fnew-abi -fno-honor-std'" check-g++
|
make RUNTESTFLAGS="--tool_opts '-fnew-abi -fno-honor-std'" check-g++
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
How can I run the test suite with multiple options?
|
How can I run the test suite with multiple options?
|
|
|
If you invoke runtest directly, you can use the --target_board option, e.g:
|
If you invoke runtest directly, you can use the --target_board option, e.g:
|
runtest --target_board "unix{-fPIC,-fpic,}"
|
runtest --target_board "unix{-fPIC,-fpic,}"
|
|
|
Or, if you use make check you can use the make variable RUNTESTFLAGS, e.g:
|
Or, if you use make check you can use the make variable RUNTESTFLAGS, e.g:
|
make RUNTESTFLAGS="--target_board 'unix{-fPIC,-fpic,}'" check-gcc
|
make RUNTESTFLAGS="--target_board 'unix{-fPIC,-fpic,}'" check-gcc
|
|
|
Either of these examples will run the tests three times. Once with -fPIC,
|
Either of these examples will run the tests three times. Once with -fPIC,
|
once with -fpic, and once with no additional flags.
|
once with -fpic, and once with no additional flags.
|
|
|
This technique is particularly useful on multilibbed targets.
|
This technique is particularly useful on multilibbed targets.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
Miscellaneous
|
Miscellaneous
|
|
|
Friend Templates
|
Friend Templates
|
|
|
In order to make a specialization of a template function a friend of a
|
In order to make a specialization of a template function a friend of a
|
(possibly template) class, you must explicitly state that the friend
|
(possibly template) class, you must explicitly state that the friend
|
function is a template, by appending angle brackets to its name, and this
|
function is a template, by appending angle brackets to its name, and this
|
template function must have been declared already. Here's an example:
|
template function must have been declared already. Here's an example:
|
template class foo {
|
template class foo {
|
friend void bar(foo);
|
friend void bar(foo);
|
}
|
}
|
|
|
The above declaration declares a non-template function named bar, so it must
|
The above declaration declares a non-template function named bar, so it must
|
be explicitly defined for each specialization of foo. A template definition
|
be explicitly defined for each specialization of foo. A template definition
|
of bar won't do, because it is unrelated with the non-template declaration
|
of bar won't do, because it is unrelated with the non-template declaration
|
above. So you'd have to end up writing:
|
above. So you'd have to end up writing:
|
void bar(foo) { /* ... */ }
|
void bar(foo) { /* ... */ }
|
void bar(foo) { /* ... */ }
|
void bar(foo) { /* ... */ }
|
|
|
If you meant bar to be a template function, you should have forward-declared
|
If you meant bar to be a template function, you should have forward-declared
|
it as follows. Note that, since the template function declaration refers to
|
it as follows. Note that, since the template function declaration refers to
|
the template class, the template class must be forward-declared too:
|
the template class, the template class must be forward-declared too:
|
template
|
template
|
class foo;
|
class foo;
|
|
|
template
|
template
|
void bar(foo);
|
void bar(foo);
|
|
|
template
|
template
|
class foo {
|
class foo {
|
friend void bar<>(foo);
|
friend void bar<>(foo);
|
};
|
};
|
|
|
template
|
template
|
void bar(foo) { /* ... */ }
|
void bar(foo) { /* ... */ }
|
|
|
In this case, the template argument list could be left empty, because it can
|
In this case, the template argument list could be left empty, because it can
|
be implicitly deduced from the function arguments, but the angle brackets
|
be implicitly deduced from the function arguments, but the angle brackets
|
must be present, otherwise the declaration will be taken as a non-template
|
must be present, otherwise the declaration will be taken as a non-template
|
function. Furthermore, in some cases, you may have to explicitly specify the
|
function. Furthermore, in some cases, you may have to explicitly specify the
|
template arguments, to remove ambiguity.
|
template arguments, to remove ambiguity.
|
|
|
An error in the last public comment draft of the ANSI/ISO C++ Standard and
|
An error in the last public comment draft of the ANSI/ISO C++ Standard and
|
the fact that previous releases of GCC would accept such friend declarations
|
the fact that previous releases of GCC would accept such friend declarations
|
as template declarations has led people to believe that the forward
|
as template declarations has led people to believe that the forward
|
declaration was not necessary, but, according to the final version of the
|
declaration was not necessary, but, according to the final version of the
|
Standard, it is.
|
Standard, it is.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
dynamic_cast, throw, typeid don't work with shared libraries
|
dynamic_cast, throw, typeid don't work with shared libraries
|
|
|
The new C++ ABI in the GCC 3.0 series uses address comparisons, rather than
|
The new C++ ABI in the GCC 3.0 series uses address comparisons, rather than
|
string compares, to determine type equality. This leads to better
|
string compares, to determine type equality. This leads to better
|
performance. Like other objects that have to be present in the final
|
performance. Like other objects that have to be present in the final
|
executable, these std::type_info objects have what is called vague linkage
|
executable, these std::type_info objects have what is called vague linkage
|
because they are not tightly bound to any one particular translation unit
|
because they are not tightly bound to any one particular translation unit
|
(object file). The compiler has to emit them in any translation unit that
|
(object file). The compiler has to emit them in any translation unit that
|
requires their presence, and then rely on the linking and loading process to
|
requires their presence, and then rely on the linking and loading process to
|
make sure that only one of them is active in the final executable. With
|
make sure that only one of them is active in the final executable. With
|
static linking all of these symbols are resolved at link time, but with
|
static linking all of these symbols are resolved at link time, but with
|
dynamic linking, further resolution occurs at load time. You have to ensure
|
dynamic linking, further resolution occurs at load time. You have to ensure
|
that objects within a shared library are resolved against objects in the
|
that objects within a shared library are resolved against objects in the
|
executable and other shared libraries.
|
executable and other shared libraries.
|
* For a program which is linked against a shared library, no additional
|
* For a program which is linked against a shared library, no additional
|
precautions are needed.
|
precautions are needed.
|
* You cannot create a shared library with the "-Bsymbolic" option, as that
|
* You cannot create a shared library with the "-Bsymbolic" option, as that
|
prevents the resolution described above.
|
prevents the resolution described above.
|
* If you use dlopen to explicitly load code from a shared library, you
|
* If you use dlopen to explicitly load code from a shared library, you
|
must do several things. First, export global symbols from the executable
|
must do several things. First, export global symbols from the executable
|
by linking it with the "-E" flag (you will have to specify this as
|
by linking it with the "-E" flag (you will have to specify this as
|
"-Wl,-E" if you are invoking the linker in the usual manner from the
|
"-Wl,-E" if you are invoking the linker in the usual manner from the
|
compiler driver, g++). You must also make the external symbols in the
|
compiler driver, g++). You must also make the external symbols in the
|
loaded library available for subsequent libraries by providing the
|
loaded library available for subsequent libraries by providing the
|
RTLD_GLOBAL flag to dlopen. The symbol resolution can be immediate or
|
RTLD_GLOBAL flag to dlopen. The symbol resolution can be immediate or
|
lazy.
|
lazy.
|
|
|
Template instantiations are another, user visible, case of objects with
|
Template instantiations are another, user visible, case of objects with
|
vague linkage, which needs similar resolution. If you do not take the above
|
vague linkage, which needs similar resolution. If you do not take the above
|
precautions, you may discover that a template instantiation with the same
|
precautions, you may discover that a template instantiation with the same
|
argument list, but instantiated in multiple translation units, has several
|
argument list, but instantiated in multiple translation units, has several
|
addresses, depending in which translation unit the address is taken. (This
|
addresses, depending in which translation unit the address is taken. (This
|
is not an exhaustive list of the kind of objects which have vague linkage
|
is not an exhaustive list of the kind of objects which have vague linkage
|
and are expected to be resolved during linking & loading.)
|
and are expected to be resolved during linking & loading.)
|
|
|
If you are worried about different objects with the same name colliding
|
If you are worried about different objects with the same name colliding
|
during the linking or loading process, then you should use namespaces to
|
during the linking or loading process, then you should use namespaces to
|
disambiguate them. Giving distinct objects with global linkage the same name
|
disambiguate them. Giving distinct objects with global linkage the same name
|
is a violation of the One Definition Rule (ODR) [basic.def.odr].
|
is a violation of the One Definition Rule (ODR) [basic.def.odr].
|
|
|
For more details about the way that GCC implements these and other C++
|
For more details about the way that GCC implements these and other C++
|
features, please read the [32]ABI specification. Note the std::type_info
|
features, please read the [32]ABI specification. Note the std::type_info
|
objects which must be resolved all begin with "_ZTS". Refer to ld's
|
objects which must be resolved all begin with "_ZTS". Refer to ld's
|
documentation for a description of the "-E" & "-Bsymbolic" flags.
|
documentation for a description of the "-E" & "-Bsymbolic" flags.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
Why do I need autoconf, bison, xgettext, automake, etc?
|
Why do I need autoconf, bison, xgettext, automake, etc?
|
|
|
If you're using diffs up dated from one snapshot to the next, or if you're
|
If you're using diffs up dated from one snapshot to the next, or if you're
|
using the SVN repository, you may need several additional programs to build
|
using the SVN repository, you may need several additional programs to build
|
GCC.
|
GCC.
|
|
|
These include, but are not necessarily limited to autoconf, automake, bison,
|
These include, but are not necessarily limited to autoconf, automake, bison,
|
and xgettext.
|
and xgettext.
|
|
|
This is necessary because neither diff nor cvs keep timestamps correct. This
|
This is necessary because neither diff nor cvs keep timestamps correct. This
|
causes problems for generated files as "make" may think those generated
|
causes problems for generated files as "make" may think those generated
|
files are out of date and try to regenerate them.
|
files are out of date and try to regenerate them.
|
|
|
An easy way to work around this problem is to use the gcc_update script in
|
An easy way to work around this problem is to use the gcc_update script in
|
the contrib subdirectory of GCC, which handles this transparently without
|
the contrib subdirectory of GCC, which handles this transparently without
|
requiring installation of any additional tools.
|
requiring installation of any additional tools.
|
|
|
When building from diffs or SVN or if you modified some sources, you may
|
When building from diffs or SVN or if you modified some sources, you may
|
also need to obtain development versions of some GNU tools, as the
|
also need to obtain development versions of some GNU tools, as the
|
production versions do not necessarily handle all features needed to rebuild
|
production versions do not necessarily handle all features needed to rebuild
|
GCC.
|
GCC.
|
|
|
In general, the current versions of these tools from
|
In general, the current versions of these tools from
|
[33]ftp://ftp.gnu.org/gnu/ will work. At present, Autoconf 2.50 is not
|
[33]ftp://ftp.gnu.org/gnu/ will work. At present, Autoconf 2.50 is not
|
supported, and you will need to use Autoconf 2.13; work is in progress to
|
supported, and you will need to use Autoconf 2.13; work is in progress to
|
fix this problem. Also look at [34]ftp://gcc.gnu.org/pub/gcc/infrastructure/
|
fix this problem. Also look at [34]ftp://gcc.gnu.org/pub/gcc/infrastructure/
|
for any special versions of packages.
|
for any special versions of packages.
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
Why can't I build a shared library?
|
Why can't I build a shared library?
|
|
|
When building a shared library you may get an error message from the linker
|
When building a shared library you may get an error message from the linker
|
like `assert pure-text failed:' or `DP relative code in file'.
|
like `assert pure-text failed:' or `DP relative code in file'.
|
|
|
This kind of error occurs when you've failed to provide proper flags to gcc
|
This kind of error occurs when you've failed to provide proper flags to gcc
|
when linking the shared library.
|
when linking the shared library.
|
|
|
You can get this error even if all the .o files for the shared library were
|
You can get this error even if all the .o files for the shared library were
|
compiled with the proper PIC option. When building a shared library, gcc
|
compiled with the proper PIC option. When building a shared library, gcc
|
will compile additional code to be included in the library. That additional
|
will compile additional code to be included in the library. That additional
|
code must also be compiled with the proper PIC option.
|
code must also be compiled with the proper PIC option.
|
|
|
Adding the proper PIC option (-fpic or -fPIC) to the link line which creates
|
Adding the proper PIC option (-fpic or -fPIC) to the link line which creates
|
the shared library will fix this problem on targets that support PIC in this
|
the shared library will fix this problem on targets that support PIC in this
|
manner. For example:
|
manner. For example:
|
gcc -c -fPIC myfile.c
|
gcc -c -fPIC myfile.c
|
gcc -shared -o libmyfile.so -fPIC myfile.o
|
gcc -shared -o libmyfile.so -fPIC myfile.o
|
_________________________________________________________________
|
_________________________________________________________________
|
|
|
When building C++, the linker says my constructors, destructors or virtual
|
When building C++, the linker says my constructors, destructors or virtual
|
tables are undefined, but I defined them
|
tables are undefined, but I defined them
|
|
|
The ISO C++ Standard specifies that all virtual methods of a class that are
|
The ISO C++ Standard specifies that all virtual methods of a class that are
|
not pure-virtual must be defined, but does not require any diagnostic for
|
not pure-virtual must be defined, but does not require any diagnostic for
|
violations of this rule [class.virtual]/8. Based on this assumption, GCC
|
violations of this rule [class.virtual]/8. Based on this assumption, GCC
|
will only emit the implicitly defined constructors, the assignment operator,
|
will only emit the implicitly defined constructors, the assignment operator,
|
the destructor and the virtual table of a class in the translation unit that
|
the destructor and the virtual table of a class in the translation unit that
|
defines its first such non-inline method.
|
defines its first such non-inline method.
|
|
|
Therefore, if you fail to define this particular method, the linker may
|
Therefore, if you fail to define this particular method, the linker may
|
complain about the lack of definitions for apparently unrelated symbols.
|
complain about the lack of definitions for apparently unrelated symbols.
|
Unfortunately, in order to improve this error message, it might be necessary
|
Unfortunately, in order to improve this error message, it might be necessary
|
to change the linker, and this can't always be done.
|
to change the linker, and this can't always be done.
|
|
|
The solution is to ensure that all virtual methods that are not pure are
|
The solution is to ensure that all virtual methods that are not pure are
|
defined. Note that a destructor must be defined even if it is declared
|
defined. Note that a destructor must be defined even if it is declared
|
pure-virtual [class.dtor]/7.
|
pure-virtual [class.dtor]/7.
|
|
|
References
|
References
|
|
|
1. http://gcc.gnu.org/faq.html
|
1. http://gcc.gnu.org/faq.html
|
2. http://c-faq.com/
|
2. http://c-faq.com/
|
3. http://www.comeaucomputing.com/csc/faq.html
|
3. http://www.comeaucomputing.com/csc/faq.html
|
4. http://www.fortran.com/fortran/info.html
|
4. http://www.fortran.com/fortran/info.html
|
5. http://gcc.gnu.org/onlinedocs/libstdc++/faq/index.html
|
5. http://gcc.gnu.org/onlinedocs/libstdc++/faq/index.html
|
6. http://gcc.gnu.org/java/faq.html
|
6. http://gcc.gnu.org/java/faq.html
|
7. http://gcc.gnu.org/faq.html#general
|
7. http://gcc.gnu.org/faq.html#general
|
8. http://gcc.gnu.org/faq.html#support
|
8. http://gcc.gnu.org/faq.html#support
|
9. http://gcc.gnu.org/faq.html#platforms
|
9. http://gcc.gnu.org/faq.html#platforms
|
10. http://gcc.gnu.org/faq.html#installation
|
10. http://gcc.gnu.org/faq.html#installation
|
11. http://gcc.gnu.org/faq.html#multiple
|
11. http://gcc.gnu.org/faq.html#multiple
|
12. http://gcc.gnu.org/faq.html#rpath
|
12. http://gcc.gnu.org/faq.html#rpath
|
13. http://gcc.gnu.org/faq.html#rpath
|
13. http://gcc.gnu.org/faq.html#rpath
|
14. http://gcc.gnu.org/faq.html#gas
|
14. http://gcc.gnu.org/faq.html#gas
|
15. http://gcc.gnu.org/faq.html#environ
|
15. http://gcc.gnu.org/faq.html#environ
|
16. http://gcc.gnu.org/faq.html#optimizing
|
16. http://gcc.gnu.org/faq.html#optimizing
|
17. http://gcc.gnu.org/faq.html#iconv
|
17. http://gcc.gnu.org/faq.html#iconv
|
18. http://gcc.gnu.org/faq.html#testsuite
|
18. http://gcc.gnu.org/faq.html#testsuite
|
19. http://gcc.gnu.org/faq.html#testoptions
|
19. http://gcc.gnu.org/faq.html#testoptions
|
20. http://gcc.gnu.org/faq.html#multipletests
|
20. http://gcc.gnu.org/faq.html#multipletests
|
21. http://gcc.gnu.org/faq.html#misc
|
21. http://gcc.gnu.org/faq.html#misc
|
22. http://gcc.gnu.org/faq.html#friend
|
22. http://gcc.gnu.org/faq.html#friend
|
23. http://gcc.gnu.org/faq.html#dso
|
23. http://gcc.gnu.org/faq.html#dso
|
24. http://gcc.gnu.org/faq.html#generated_files
|
24. http://gcc.gnu.org/faq.html#generated_files
|
25. http://gcc.gnu.org/faq.html#picflag-needed
|
25. http://gcc.gnu.org/faq.html#picflag-needed
|
26. http://gcc.gnu.org/faq.html#vtables
|
26. http://gcc.gnu.org/faq.html#vtables
|
27. http://gcc.gnu.org/bugs.html
|
27. http://gcc.gnu.org/bugs.html
|
28. http://gcc.gnu.org/install/specific.html
|
28. http://gcc.gnu.org/install/specific.html
|
29. http://gcc.gnu.org/buildstat.html
|
29. http://gcc.gnu.org/buildstat.html
|
30. http://gcc.gnu.org/faq.html#gas
|
30. http://gcc.gnu.org/faq.html#gas
|
31. http://gcc.gnu.org/install/specific.html
|
31. http://gcc.gnu.org/install/specific.html
|
32. http://www.codesourcery.com/cxx-abi/
|
32. http://www.codesourcery.com/cxx-abi/
|
33. ftp://ftp.gnu.org/gnu/
|
33. ftp://ftp.gnu.org/gnu/
|
34. ftp://gcc.gnu.org/pub/gcc/infrastructure/
|
34. ftp://gcc.gnu.org/pub/gcc/infrastructure/
|
|
|
