mirror/gcc
2
0
Fork 0
mirror of git://gcc.gnu.org/git/gcc.git synced 2024-12-29 07:04:44 +08:00
Code Issues Packages Projects Releases Wiki Activity
87bc7fa6aa
gcc/libstdc++-v3/docs/html/faq/index.txt
Nathan Myers 2dac8f87e8 index.html (5.8): New entry on ABIs. 
2001-11-07  Nathan Myers  <ncm@cantrip.org>

	* docs/html/faq/index.html (5.8):  New entry on ABIs.
	* docs/html/faq/index.txt:  Regenerate.

From-SVN: r46836
2001-11-07 21:08:53 +00:00

813 lines
37 KiB
Plaintext
Raw Blame History

libstdc++ Frequently Asked Questions
The latest version of this document is always available at
[1]http://gcc.gnu.org/onlinedocs/libstdc++/faq/.
To the [2]libstdc++-v3 homepage.
_________________________________________________________________
Questions
1. [3]General Information
1. [4]What is libstdc++-v3?
2. [5]Why should I use libstdc++?
3. [6]Who's in charge of it?
4. [7]How do I get libstdc++?
5. [8]When is libstdc++ going to be finished?
6. [9]How do I contribute to the effort?
7. [10]What happened to libg++? I need that!
8. [11]What if I have more questions?
9. [12]What are the license terms for libstdc++-v3?
2. [13]Installation
1. [14]How do I install libstdc++-v3?
2. [15][removed]
3. [16]What is this CVS thing that you keep mentioning?
4. [17]How do I know if it works?
5. [18]This library is HUGE! And what's libsupc++?
3. [19]Platform-Specific Issues
1. [20]Can libstdc++-v3 be used with <my favorite compiler>?
2. [21][removed]
3. [22]Building under DEC OSF kills the assembler
4. [23]I can't use 'long long' on Solaris
4. [24]Known Bugs and Non-Bugs
1. [25]What works already?
2. [26]Bugs in gcc/g++ (not libstdc++-v3)
3. [27]Bugs in the C++ language/lib specification
4. [28]Things in libstdc++ that look like bugs
o [29]reopening a stream fails
o [30]-Weffc++ complains too much
o [31]"ambiguous overloads" after including an old-style
header
o [32]The g++-3 headers are not ours
o [33]compilation errors from streambuf.h
o [34]errors about *Cconcept and constraints in the STL...
5. [35]Aw, that's easy to fix!
5. [36]Miscellaneous
1. [37]string::iterator is not char*; vector<T>::iterator is not
T*
2. [38]What's next after libstdc++-v3?
3. [39]What about the STL from SGI?
4. [40]Extensions and Backward Compatibility
5. [41][removed]
6. [42]Is libstdc++-v3 thread-safe?
7. [43]How do I get a copy of the ISO C++ Standard?
8. [44]What's an ABI and why is it so messy?
_________________________________________________________________
1.0 General Information
1.1 What is libstdc++-v3?
The GNU Standard C++ Library v3, or libstdc++-2.9x, is an ongoing
project to implement the ISO 14882 Standard C++ library as described
in chapters 17 through 27 and annex D. As the library reaches stable
plateaus, it is captured in a snapshot and released. The current
release is [45]the eleventh snapshot. For those who want to see
exactly how far the project has come, or just want the latest
bleeding-edge code, the up-to-date source is available over anonymous
CVS, and can even be browsed over the Web (see below).
A more formal description of the V3 goals can be found in the official
[46]design document.
_________________________________________________________________
1.2 Why should I use libstdc++?
The completion of the ISO C++ standardization gave the C++ community a
powerful set of reuseable tools in the form of the C++ Standard
Library. However, all existing C++ implementations are (as the Draft
Standard used to say) "incomplet and incorrekt," and many suffer from
limitations of the compilers that use them.
The GNU C/C++/FORTRAN/<pick-a-language> compiler (gcc, g++, etc) is
widely considered to be one of the leading compilers in the world. Its
development has recently been taken over by the [47]GCC team. All of
the rapid development and near-legendary [48]portability that are the
hallmarks of an open-source project are being applied to libstdc++.
That means that all of the Standard classes and functions (such as
string, vector<>, iostreams, and algorithms) will be freely available
and fully compliant. Programmers will no longer need to "roll their
own" nor be worried about platform-specific incompatabilities.
_________________________________________________________________
1.3 Who's in charge of it?
The libstdc++ project is contributed to by several developers all over
the world, in the same way as GCC or Linux. Benjamin Kosnik, Gabriel
Dos Reis, Phil Edwards, and Ulrich Drepper are the lead maintainers of
the CVS archive.
Development and discussion is held on the libstdc++ mailing list.
Subscribing to the list, or searching the list archives, is open to
everyone. You can read instructions for doing so on the [49]homepage.
If you have questions, ideas, code, or are just curious, sign up!
_________________________________________________________________
1.4 How do I get libstdc++?
The eleventh (and latest) snapshot of libstdc++-v3 is [50]available
via ftp. The filename is libstdc++-2.92.tar.gz.
The [51]homepage has instructions for retrieving the latest CVS
sources, and for browsing the CVS sources over the web.
The subset commonly known as the Standard Template Library (chapters
23 through 25, mostly) is adapted from the final release of the SGI
STL.
_________________________________________________________________
1.5 When is libstdc++ going to be finished?
Nathan Myers gave the best of all possible answers, responding to a
Usenet article asking this question: Sooner, if you help.
_________________________________________________________________
1.6 How do I contribute to the effort?
Here is [52]a page devoted to this topic. Subscribing to the mailing
list (see above, or the homepage) is a very good idea if you have
something to contribute, or if you have spare time and want to help.
Contributions don't have to be in the form of source code; anybody who
is willing to help write documentation, for example, or has found a
bug in code that we all thought was working, is more than welcome!
_________________________________________________________________
1.7 What happened to libg++? I need that!
The most recent libg++ README states that libg++ is no longer being
actively maintained. It should not be used for new projects, and is
only being kicked along to support older code.
The libg++ was designed and created when there was no Standard to
provide guidance. Classes like linked lists are now provided for by
list<T> and do not need to be created by genclass. (For that matter,
templates exist now and are well-supported, whereas genclass (mostly)
predates them.)
There are other classes in libg++ that are not specified in the ISO
Standard (e.g., statistical analysis). While there are a lot of really
useful things that are used by a lot of people (e.g., statistics :-),
the Standards Committee couldn't include everything, and so a lot of
those "obvious" classes didn't get included.
Since libstdc++ is an implementation of the Standard Library, we have
no plans at this time to include non-Standard utilities in the
implementation, however handy they are. (The extensions provided in
the SGI STL aren't maintained by us and don't get a lot of our
attention, because they don't require a lot of our time.) It is
entirely plausable that the "useful stuff" from libg++ might be
extracted into an updated utilities library, but nobody has stated
such a project yet.
(The [53]Boost site houses free C++ libraries that do varying things,
and happened to be started by members of the Standards Committee.
Certain "useful stuff" classes will probably migrate there.)
For the bold and/or desperate, the [54]GCC FAQ describes where to find
the last libg++ source.
_________________________________________________________________
1.8 What if I have more questions?
If you have read the README and RELEASE-NOTES files, and your question
remains unanswered, then just ask the mailing list. At present, you do
not need to be subscribed to the list to send a message to it. More
information is available on the homepage (including how to browse the
list archives); to send to the list, use [55]libstdc++@gcc.gnu.org.
If you have a question that you think should be included here, or if
you have a question about a question/answer here, contact [56]Phil
Edwards or [57]Gabriel Dos Reis.
_________________________________________________________________
1.9 What are the license terms for libstdc++-v3?
See [58]our license description for these and related questions.
_________________________________________________________________
2.0 Installation
2.1 How do I install libstdc++-v3?
Complete instructions are not given here (this is a FAQ, not an
installation document), but the tools required are few:
* A 3.x release of GCC. Note that building GCC is much easier and
more automated than building the GCC 2.[78] series was. If you are
using GCC 2.95, you can still build earlier snapshots of
libstdc++.
* GNU Make is recommended, but should not be required.
* The GNU Autotools are needed if you are messing with the configury
or makefiles.
The file [59]documentation.html provides a good overview of the steps
necessary to build, install, and use the library. Instructions for
configuring the library with new flags such as --enable-threads are
there also, as well as patches and instructions for working with GCC
2.95.
The top-level install.html and [60]RELEASE-NOTES files contain the
exact build and installation instructions. You may wish to browse
those files over CVSweb ahead of time to get a feel for what's
required. RELEASE-NOTES is located in the ".../docs/17_intro/"
directory of the distribution.
_________________________________________________________________
2.2 [removed]
This question has become moot and has been removed. The stub is here
to preserve numbering (and hence links/bookmarks).
_________________________________________________________________
2.3 What is this CVS thing that you keep mentioning?
The Concurrent Versions System is one of several revision control
packages. It was selected for GNU projects because it's free (speech),
free (beer), and very high quality. The [61]CVS entry in the GNU
software catalogue has a better description as well as a [62]link to
the makers of CVS.
The "anonymous client checkout" feature of CVS is similar to anonymous
FTP in that it allows anyone to retrieve the latest libstdc++ sources.
After the first of April, American users will have a "/pharmacy"
command-line option...
_________________________________________________________________
2.4 How do I know if it works?
libstdc++-v3 comes with its own testsuite. You do not need to actually
install the library ("make install") to run the testsuite.
To run the testsuite on the library after building it, use "make
check" while in your build directory. To run the testsuite on the
library after building and installing it, use "make check-install"
instead.
If you find bugs in the testsuite programs themselves, or if you think
of a new test program that should be added to the suite, please write
up your idea and send it to the list!
_________________________________________________________________
2.4 This library is HUGE! And what's libsupc++?
Usually the size of libraries on disk isn't noticeable. When a link
editor (or simply "linker") pulls things from a static archive
library, only the necessary object files are copied into your
executable, not the entire library. Unfortunately, even if you only
need a single function or variable from an object file, the entire
object file is extracted. (There's nothing unique to C++ or
libstdc++-v3 about this; it's just common behavior, given here for
background reasons.)
Some of the object files which make up libstdc++.a are rather large.
If you create a statically-linked executable with -static, those large
object files are suddenly part of your executable. Historically the
best way around this was to only place a very few functions (often
only a single one) in each source/object file; then extracting a
single function is the same as extracting a single .o file. For
libstdc++-v3 this is only possible to a certain extent; the object
files in question contain template classes and template functions,
pre-instantiated, and splitting those up causes severe maintenance
headaches.
It's not a bug, and it's not really a problem. Nevertheless, some
people don't like it, so here are two pseudo-solutions:
If the only functions from libstdc++.a which you need are language
support functions (those listed in [63]clause 18 of the standard,
e.g., new and delete), then try linking against libsupc++.a (usually
specifying -lsupc++ when calling g++ for the final link step will do
it). This library contains only those support routines, one per object
file. But if you are using anything from the rest of the library, such
as IOStreams or vectors, then you'll still need pieces from
libstdc++.a.
The second method is one we hope to incorporate into the library build
process. Some platforms can place each function and variable into its
own section in a .o file. The GNU linker can then perform garbage
collection on unused sections; this reduces the situation to only
copying needed functions into the executable, as before, but all
happens automatically.
Unfortunately the garbage collection in GNU ld is buggy; sections
(corresponding to functions and variables) which are used are
mistakenly removed, leading to horrible crashes when your executable
starts up. For the time being, this feature is not used when building
the library.
_________________________________________________________________
3.0 Platform-Specific Issues
3.1 Can libstdc++-v3 be used with <my favorite compiler>?
Probably not. Yet.
Because GCC advances so rapidly, development and testing of libstdc++
is being done almost entirely under that compiler. If you are curious
about whether other, lesser compilers (*grin*) support libstdc++, you
are more than welcome to try. Configuring and building the library
(see above) will still require certain tools, however. Also keep in
mind that building libstdc++ does not imply that your compiler will be
able to use all of the features found in the C++ Standard Library.
Since the goal of ISO Standardization is for all C++ implementations
to be able to share code, the final libstdc++ should, in theory, be
useable under any ISO-compliant compiler. It will still be targeted
and optimized for GCC/g++, however.
_________________________________________________________________
3.2 [removed]
This question has become moot and has been removed. The stub is here
to preserve numbering (and hence links/bookmarks).
_________________________________________________________________
3.3 Building DEC OSF kills the assembler
The atomicity.h header for the Alpha processor currently uses
pseudo-operators which the DEC assembler doesn't understand (in
particular, .subsection and .previous). The simple solution is to
install GNU as and arrange for the GCC build to use it (or merge the
sources and build it during the bootstrap).
Anyone who [64]knows the DEC assembler well enough to provide the
equivalent of these two pseudos would win praise and accolades from
many.
_________________________________________________________________
3.4 I can't use 'long long' on Solaris
By default we try to support the C99 long long type. This requires
that certain functions from your C library be present.
Up through release 3.0.2 the tests performed were too general, and
this feature was disabled when it did not need to be. The most
commonly reported platform affected was Solaris.
This has been fixed for 3.0.3 and onwards.
_________________________________________________________________
4.0 Known Bugs and Non-Bugs
Note that this section can get rapdily outdated -- such is the nature
of an open-source project. For the latest information, join the
mailing list or look through recent archives. The RELEASE- NOTES and
BUGS files are generally kept up-to-date.
For 3.0.1, the most common "bug" is an apparently missing "../" in
include/Makefile, resulting in files like gthr.h and gthr-single.h not
being found.
Please read [65]the configuration instructions for GCC, specifically
the part about configuring in a separate build directory, and how
strongly recommended it is. Building in the source directory is
fragile, is rarely tested, and tends to break, as in this case. This
was fixed for 3.0.2.
Please do not report these as bugs. We know about them. Reporting this
-- or any other problem that's already been fixed -- hinders the
development of GCC, because we have to take time to respond to your
report. Thank you.
4.1 What works already?
This is a verbatim clip from the "Status" section of the RELEASE-NOTES
for the latest snapshot.
New:
---
- preliminary doxygen documentation has been added. Running "make
doxygen" in the libstdc++-v3 build directory will generate HTML
documentation that can be used to cross-reference names and files in
the library.
- a dejagnu based testing framework has been added
- a new implementation of the concept checking code has been ported
from the boost libraries.
- support for -fno-exceptions has been added
- stdexcept was re-written
- using deprecated or antiquated headers now gives a warning
- the stdio interface to iostreams has been tweaked, and now works
with synchronized c/c++ io
- new libsupc++ routines implementing the IA-64 C++ ABI.
- HPUX configuration files
- support for AIX added
- a lot of bugs were fixed.
- preliminary named locales implemented
- portability improvements made to generation of <limits>
- speedups to improve configuration time.
- DJGPP support added.
- support for dlopening shared libstdc++
_________________________________________________________________
4.2 Bugs in gcc/g++ (not libstdc++-v3)
This is by no means meant to be complete nor exhaustive, but mentions
some problems that users may encounter when building or using
libstdc++. If you are experiencing one of these problems, you can find
more information on the libstdc++ and the GCC mailing lists.
* As of 2.91, these bugs have all been fixed. We look forward to new
ones, well, not exactly...
_________________________________________________________________
4.3 Bugs in the C++ language/lib specification
Yes, unfortunately, there are some. In a [66]message to the list,
Nathan Myers announced that he has started a list of problems in the
ISO C++ Standard itself, especially with regard to the chapters that
concern the library. The list itself is [67]posted on his website.
Developers who are having problems interpreting the Standard may wish
to consult his notes.
For those people who are not part of the ISO Library Group (i.e.,
nearly all of us needing to read this page in the first place :-), a
public list of the library defects is occasionally published [68]here.
Some of these have resulted in [69]code changes.
_________________________________________________________________
4.4 Things in libstdc++ that look like bugs
There are things which are not bugs in the compiler (4.2) nor the
language specification (4.3), but aren't really bugs in libstdc++,
either. Really! Please do not report these as bugs.
-Weffc++ The biggest of these is the quadzillions of warnings about
the library headers emitted when -Weffc++ is used. Making libstdc++
"-Weffc++-clean" is not a goal of the project, for a few reasons.
Mainly, that option tries to enforce object-oriented programming,
while the Standard Library isn't necessarily trying to be OO. There
are multiple solutions under discussion.
reopening a stream fails Did I just say that -Weffc++ was our biggest
false-bug report? I lied. (It used to be.) Today it seems to be
reports that after executing a sequence like
#include <fstream>
...
std::fstream fs("a_file");
// .
// . do things with fs...
// .
fs.close();
fs.open("a_new_file");
all operations on the re-opened fs will fail, or at least act very
strangely. Yes, they often will, especially if fs reached the EOF
state on the previous file. The reason is that the state flags are not
cleared on a successful call to open(). The standard unfortunately did
not specify behavior in this case, and to everybody's great sorrow,
the [70]proposed LWG resolution (see DR #22) is to leave the flags
unchanged. You must insert a call to fs.clear() between the calls to
close() and open(), and then everything will work like we all expect
it to work.
rel_ops Another is the rel_ops namespace and the template comparison
operator functions contained therein. If they become visible in the
same namespace as other comparison functions (e.g., 'using' them and
the <iterator> header), then you will suddenly be faced with huge
numbers of ambiguity errors. This was discussed on the -v3 list;
Nathan Myers [71]sums things up here.
The g++-3 headers are not ours
If you have found an extremely broken header file which is causing
problems for you, look carefully before submitting a "high" priority
bug report (which you probably shouldn't do anyhow; see the last
paragraph of the page describing [72]the GCC bug database).
If the headers are in ${prefix}/include/g++-3, then you are using the
old libstdc++-v2 library, which is nonstandard and unmaintained. Do
not report problems with -v2 to the -v3 mailing list.
Currently our header files are installed in ${prefix}/include/g++-v3
(see the 'v'?). This may change with the next release of GCC, as it
may be too confusing, but [73]the question has not yet been decided.
glibc If you're on a GNU/Linux system and have just upgraded to glibc
2.2, but are still using gcc 2.95.2, then you should have read the
glibc FAQ, specifically 2.34:
2.34. When compiling C++ programs, I get a compilation error in streambuf.h.
{BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
apply a patch to the include files in /usr/include/g++, because the fpos_t
type has changed in glibc 2.2. The patch is at
http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
Note that 2.95.x shipped with the [74]old v2 library which is no
longer maintained. Also note that gcc 2.95.3 fixes this problem, but
requires a separate patch for libstdc++-v3.
concept checks If you see compilation errors containing messages about
fooConcept and a constraints member function, then most likely you
have violated one of the requirements for types used during
instantiation of template containers and functions. For example,
EqualityComparableConcept appears if your types must be comparable
with == and you have not provided this capability (a typo, or wrong
visibility, or you just plain forgot, etc).
More information, including how to optionally enable/disable the
checks, is available [75]here.
_________________________________________________________________
4.5 Aw, that's easy to fix!
If you have found a bug in the library and you think you have a
working fix, then send it in! The main GCC site has a page on
[76]submitting patches that covers the procedure, but for libstdc++
you should also send the patch to our mailing list in addition to the
GCC patches mailing list. The libstdc++ [77]contributors' page also
talks about how to submit patches.
In addition to the description, the patch, and the ChangeLog entry, it
is a Good Thing if you can additionally create a small test program to
test for the presence of the bug that your patch fixes. Bugs have a
way of being reintroduced; if an old bug creeps back in, it will be
caught immediately by the [78]testsuite -- but only if such a test
exists.
_________________________________________________________________
5.0 Miscellaneous
5.1 string::iterator is not char*; vector<T>::iterator is not T*
If you have code that depends on container<T> iterators being
implemented as pointer-to-T, your code is broken.
While there are arguments for iterators to be implemented in that
manner, A) they aren't very good ones in the long term, and B) they
were never guaranteed by the Standard anyway. The type-safety achieved
by making iterators a real class rather than a typedef for T*
outweighs nearly all opposing arguments.
Code which does assume that a vector iterator i is a pointer can often
be fixed by changing i in certain expressions to &*i . Future
revisions of the Standard are expected to bless this usage for
vector<> (but not for basic_string<>).
_________________________________________________________________
5.2 What's next after libstdc++-v3?
Hopefully, not much. The goal of libstdc++-v3 is to produce a
fully-compliant, fully-portable Standard Library. After that, we're
mostly done: there won't be any more compliance work to do. However:
1. The ISO Committee will meet periodically to review Defect Reports
in the C++ Standard. Undoubtedly some of these will result in
changes to the Standard, which will be reflected in patches to
libstdc++. Some of that is already happening, see 4.2. Some of
those changes are being predicted by the library maintainers, and
we add code to the library based on what the current proposed
resolution specifies. Those additions are listed in [79]the
extensions page.
2. Performance tuning. Lots of performance tuning. This too is
already underway for post-3.0 releases, starting with memory
expansion in container classes and buffer usage in synchronized
stream objects.
3. An ABI for libstdc++ will eventually be developed, so that
multiple binary-incompatible copies of the library can be replaced
with a single backwards-compatible library, like libgcc_s.so is.
4. The current libstdc++ contains extensions to the Library which
must be explicitly requested by client code (for example, the hash
tables from SGI). Other extensions may be added to libstdc++-v3 if
they seem to be "standard" enough. (For example, the "long long"
type from C99.) Bugfixes and rewrites (to improve or fix thread
safety, for instance) will of course be a continuing task.
[80]This question about the next libstdc++ prompted some brief but
interesting [81]speculation.
_________________________________________________________________
5.3 What about the STL from SGI?
The [82]STL from SGI, version 3.3, was the most recent merge of the
STL codebase. The code in libstdc++ contains many fixes and changes,
and it is very likely that the SGI code is no longer under active
development. We expect that no future merges will take place.
In particular, string is not from SGI and makes no use of their "rope"
class (which is included as an optional extension), nor is valarray
and some others. Classes like vector<> are, however.
The FAQ for SGI's STL (one jump off of their main page) is recommended
reading.
_________________________________________________________________
5.4 Extensions and Backward Compatibility
Although you can specify -I options to make the preprocessor search
the g++-v3/ext and /backward directories, it is better to refer to
files there by their path, as in:
#include <ext/hash_map>
Extensions to the library have [83]their own page.
_________________________________________________________________
5.5 [removed]
This question has become moot and has been removed. The stub is here
to preserve numbering (and hence links/bookmarks).
_________________________________________________________________
5.6 Is libstdc++-v3 thread-safe?
When the system's libc is itself thread-safe, a non-generic
implementation of atomicity.h exists for the architecture, and gcc
itself reports a thread model other than single; libstdc++-v3 strives
to be thread-safe. The user-code must guard against concurrent method
calls which may access any particular library object's state.
Typically, the application programmer may infer what object locks must
be held based on the objects referenced in a method call. Without
getting into great detail, here is an example which requires
user-level locks:
library_class_a shared_object_a;
thread_main () {
library_class_b *object_b = new library_class_b;
shared_object_a.add_b (object_b); // must hold lock for shared_object_
a
shared_object_a.mutate (); // must hold lock for shared_object_
a
}
// Multiple copies of thread_main() are started in independent threads.
Under the assumption that object_a and object_b are never exposed to
another thread, here is an example that should not require any
user-level locks:
thread_main () {
library_class_a object_a;
library_class_b *object_b = new library_class_b;
object_a.add_b (object_b);
object_a.mutate ();
}
All library objects are safe to use in a multithreaded program as long
as each thread carefully locks out access by any other thread while it
uses any object visible to another thread. This requirement includes
both read and write access to objects; do not assume that two threads
may read a shared standard container at the same time.
See chapters [84]17 (library introduction), [85]23 (containers), and
[86]27 (I/O) for more information.
_________________________________________________________________
5.7 How do I get a copy of the ISO C++ Standard?
Copies of the full ISO 14882 standard are available on line via the
ISO mirror site for committee members. Non-members, or those who have
not paid for the privilege of sitting on the committee and sustained
their two-meeting commitment for voting rights, may get a copy of the
standard from their respective national standards organization. In the
USA, this national standards organization is ANSI and their website is
right [87]here. (And if you've already registered with them, clicking
this link will take you to directly to the place where you can [88]buy
the standard on-line.
Who is your country's member body? Visit the [89]ISO homepage and find
out!
_________________________________________________________________
5.8 What's an ABI and why is it so messy?
"ABI" stands for "Application Binary Interface." Conventionally, it
refers to a great mass of details about how arguments are arranged on
the call stack and/or in registers, and how various types are arranged
and padded in structs. A single CPU design may suffer multiple ABIs
designed by different development tool vendors who made different
choices, or even by the same vendor for different target applications
or compiler versions. In ideal circumstances the CPU designer presents
one ABI and all the OSes and compilers use it. In practice every ABI
omits details that compiler implementers (consciously or accidentally)
must choose for themselves.
That ABI definition suffices for compilers to generate code so a
program can interact safely with an OS and its lowest-level libraries.
Users usually want an ABI to encompass more detail, allowing libraries
built with different compilers (or different releases of the same
compiler!) to be linked together. For C++, this includes many more
details than for C, and CPU designers (for good reasons elaborated
below) have not stepped up to publish C++ ABIs. The details include
virtual function implementation, struct inheritance layout, name
mangling, and exception handling. Such an ABI has been defined for GNU
C++, and is immediately useful for embedded work relying only on a
"free-standing implementation" that doesn't include (much of) the
standard library. It is a good basis for the work to come.
A useful C++ ABI must also incorporate many details of the standard
library implementation. For a C ABI, the layouts of a few structs
(such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
For C++, the details include the complete set of names of functions
and types used, the offsets of class members and virtual functions,
and the actual definitions of all inlines. C++ exposes many more
library details to the caller than C does. It makes defining a
complete ABI a much bigger undertaking, and requires not just
documenting library implementation details, but carefully designing
those details so that future bug fixes and optimizations don't force
breaking the ABI.
There are ways to help isolate library implementation details from the
ABI, but they trade off against speed. Library details used in inner
loops (e.g., getchar) must be exposed and frozen for all time, but
many others may reasonably be kept hidden from user code, so they may
later be changed. Deciding which, and implementing the decisions, must
happen before you can reasonably document a candidate C++ ABI that
encompasses the standard library.
_________________________________________________________________
See [90]license.html for copying conditions. Comments and suggestions
are welcome, and may be sent to [91]the libstdc++ mailing list.
References
1. http://gcc.gnu.org/onlinedocs/libstdc++/faq/
2. http://gcc.gnu.org/libstdc++/
3. ../faq/index.html#1_0
4. ../faq/index.html#1_1
5. ../faq/index.html#1_2
6. ../faq/index.html#1_3
7. ../faq/index.html#1_4
8. ../faq/index.html#1_5
9. ../faq/index.html#1_6
10. ../faq/index.html#1_7
11. ../faq/index.html#1_8
12. ../faq/index.html#1_9
13. ../faq/index.html#2_0
14. ../faq/index.html#2_1
15. ../faq/index.html#2_2
16. ../faq/index.html#2_3
17. ../faq/index.html#2_4
18. ../faq/index.html#2_5
19. ../faq/index.html#3_0
20. ../faq/index.html#3_1
21. ../faq/index.html#3_2
22. ../faq/index.html#3_3
23. ../faq/index.html#3_4
24. ../faq/index.html#4_0
25. ../faq/index.html#4_1
26. ../faq/index.html#4_2
27. ../faq/index.html#4_3
28. ../faq/index.html#4_4
29. ../faq/index.html#4_4_iostreamclear
30. ../faq/index.html#4_4_Weff
31. ../faq/index.html#4_4_rel_ops
32. ../faq/index.html#4_4_interface
33. ../faq/index.html#4_4_glibc
34. ../faq/index.html#4_4_checks
35. ../faq/index.html#4_5
36. ../faq/index.html#5_0
37. ../faq/index.html#5_1
38. ../faq/index.html#5_2
39. ../faq/index.html#5_3
40. ../faq/index.html#5_4
41. ../faq/index.html#5_5
42. ../faq/index.html#5_6
43. ../faq/index.html#5_7
44. ../faq/index.html#5_8
45. http://gcc.gnu.org/libstdc++/download.html
46. ../17_intro/DESIGN
47. http://gcc.gnu.org/
48. http://gcc.gnu.org/gcc-2.95/buildstat.html
49. http://gcc.gnu.org/libstdc++/
50. http://gcc.gnu.org/libstdc++/download.html
51. http://gcc.gnu.org/libstdc++/
52. ../17_intro/contribute.html
53. http://www.boost.org/
54. http://gcc.gnu.org/fom_serv/cache/33.html
55. mailto:libstdc++@gcc.gnu.org
56. mailto:pme@gcc.gnu.org
57. mailto:gdr@gcc.gnu.org
58. ../17_intro/license.html
59. ../documentation.html
60. ../17_intro/RELEASE-NOTES
61. http://www.gnu.org/software/cvs/cvs.html
62. http://www.cvshome.org/
63. ../18_support/howto.html
64. http://gcc.gnu.org/ml/libstdc++/2000-12/msg00279.html
65. http://gcc.gnu.org/install/configure.html
66. http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html
67. http://www.cantrip.org/draft-bugs.txt
68. http://anubis.dkuug.dk/jtc1/sc22/wg21/
69. ../faq/index.html#5_2
70. ../ext/howto.html#5
71. http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html
72. http://gcc.gnu.org/gnatswrite.html
73. http://gcc.gnu.org/ml/gcc/2000-10/msg00732.html
74. ../faq/index.html#4_4_interface
75. ../19_diagnostics/howto.html#3
76. http://gcc.gnu.org/contribute.html
77. ../17_intro/contribute.html
78. ../faq/index.html#2_4
79. ../ext/howto.html#5
80. http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html
81. http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html
82. http://www.sgi.com/Technology/STL/
83. ../ext/howto.html
84. ../17_intro/howto.html#3
85. ../23_containers/howto.html#3
86. ../27_io/howto.html#9
87. http://www.ansi.org/
88. http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998
89. http://www.iso.ch/
90. ../17_intro/license.html
91. mailto:libstdc++@gcc.gnu.org
Reference in New Issue View Git Blame Copy Permalink