[Buildroot] [PATCH 4/4] remove Glibc_vs_uClibc document
Thomas De Schampheleire
patrickdepinguin+buildroot at gmail.com
Mon Oct 10 09:03:51 UTC 2011
On Mon, Oct 10, 2011 at 10:46 AM, Thomas Petazzoni
<thomas.petazzoni at free-electrons.com> wrote:
> This document has nothing to do with Buildroot, and is probably a
> leftover from the uClibc documentation.
>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
> Acked-by: "Yann E. MORIN" <yann.morin.1998 at anciens.enib.fr>
> Acked-by: Luca Ceresoli <luca at lucaceresoli.net>
> ---
> docs/Glibc_vs_uClibc.html | 240 ---------------------------------------------
> 1 files changed, 0 insertions(+), 240 deletions(-)
> delete mode 100644 docs/Glibc_vs_uClibc.html
>
> diff --git a/docs/Glibc_vs_uClibc.html b/docs/Glibc_vs_uClibc.html
> deleted file mode 100644
> index c14eb8c..0000000
> --- a/docs/Glibc_vs_uClibc.html
> +++ /dev/null
> @@ -1,240 +0,0 @@
> -<!--#include file="header.html" -->
> -
> -<h2>uClibc vs. glibc</h2>
> -
> -<p>
> - uClibc and Glibc are not the same -- there are a number of differences which
> - may or may not cause you problems. This document attempts to list these
> - differences and, when completed, will contain a full list of all relevant
> - differences.
> - <br><br></p>
> - <ol>
> - <li>uClibc is smaller than glibc. We attempt to maintain a glibc compatible
> - interface, allowing applications that compile with glibc to easily compile with
> - uClibc. However, we do not include _everything_ that glibc includes, and
> - therefore some applications may not compile. If this happens to you, please
> - report the failure to the uclibc mailing list, with detailed error messages.
> - </li><br>
> - <li>uClibc is much more configurable then glibc. This means that a developer
> - may have compiled uClibc in such a way that significant amounts of
> - functionality have been omitted.
> - </li><br>
> - <li>uClibc does not even attempt to ensure binary compatibility across releases.
> - When a new version of uClibc is released, you may or may not need to recompile
> - all your binaries.
> - </li><br>
> - <li><ul><li> malloc(0) in glibc returns a valid pointer to something(!?!?) while in
> - uClibc calling malloc(0) returns a NULL. The behavior of malloc(0) is listed
> - as implementation-defined by SuSv3, so both libraries are equally correct.
> - This difference also applies to realloc(NULL, 0). I personally feel glibc's
> - behavior is not particularly safe. To enable glibc behavior, one has to
> - explicitly enable the MALLOC_GLIBC_COMPAT option.
> - </li><br><li>
> - glibc's malloc() implementation has behavior that is tunable via the
> - MALLOC_CHECK_ environment variable. This is primarily used to provide extra
> - malloc debugging features. These extended malloc debugging features are not
> - available within uClibc. There are many good malloc debugging libraries
> - available for Linux (dmalloc, electric fence, valgrind, etc) that work much
> - better than the glibc extended malloc debugging. So our omitting this
> - functionality from uClibc is not a great loss.
> - </li><br>
> - </ul></li>
> - <li>uClibc does not provide a database library (libdb).
> - </li><br>
> - <li>uClibc does not support NSS (/lib/libnss_*), which allows glibc to easily
> - support various methods of authentication and DNS resolution. uClibc only
> - supports flat password files and shadow password files for storing
> - authentication information. If you need something more complex than this,
> - you can compile and install pam.
> - </li><br>
> - <li>uClibc's libresolv is only a stub. Some, but not all of the functionality
> - provided by glibc's libresolv is provided internal to uClibc. Other functions
> - are not at all implemented.
> - </li><br>
> - <li>libnsl provides support for Network Information Service (NIS) which was
> - originally called "Yellow Pages" or "YP", which is an extension of RPC invented
> - by Sun to share Unix password files over the network. I personally think NIS
> - is an evil abomination and should not be used. These days, using ldap is much
> - more effective mechanism for doing the same thing. uClibc provides a stub
> - libnsl, but has no actual support for Network Information Service (NIS).
> - We therefore, also do not provide any of the headers files provided by glibc
> - under /usr/include/rpcsvc.
> - </li><br>
> - <li>uClibc's locale support is not 100% complete yet. We are working on it.
> - </li><br>
> - <li>uClibc's math library only supports long double as inlines, and even
> - then the long double support is quite limited. Also, very few of the
> - float math functions are implemented. Stick with double and you should
> - be just fine.
> - </li><br>
> - <li>uClibc's libcrypt does not support the reentrant crypt_r, setkey_r and
> - encrypt_r, since these are not required by SuSv3.
> - </li><br>
> - <li>uClibc directly uses kernel types to define most opaque data types.
> - </li><br>
> - <li>uClibc directly uses the linux kernel's arch specific 'stuct stat'.
> - </li><br>
> - <li>uClibc's librt library currently lacks all aio routines, all clock
> - routines, and all shm routines (only the timer routines and the mq
> - routines are implemented).
> - </li><br>
> -</ol>
> -<hr>
> -<h3>Manuel's Notes</h3>
> -
> - Some general comments...<br>
> - <p>
> - The intended target for all my uClibc code is ANSI/ISO C99 and SUSv3
> - compliance. While some glibc extensions are present, many will eventually
> - be configurable. Also, even when present, the glibc-like extensions may
> - differ slightly or be more restrictive than the native glibc counterparts.
> - They are primarily meant to be porting _aides_ and not necessarily
> - drop-in replacements.
> - </p><br>
> -Now for some details...<br><br>
> -
> -<u>time functions</u><br>
> -<ol>
> -<li>Leap seconds are not supported.</li><br>
> -<li>/etc/timezone and the whole zoneinfo directory tree are not supported.
> - To set the timezone, set the TZ environment variable as specified in
> - http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html
> - or you may also create an /etc/TZ file of a single line, ending with a
> - newline, containing the TZ setting. For example
> - echo CST6CDT > /etc/TZ
> -</li><br>
> -<li>Currently, locale specific eras and alternate digits are not supported.
> - They are on my TODO list.
> -</li>
> -</ol><br>
> -<u>wide char support</u><br>
> -<ol>
> -<li>The only multibyte encoding currently supported is UTF-8. The various
> - ISO-8859-* encodings are (optionally) supported. The internal
> - representation of wchar's is assumed to be 31 bit unicode values in
> - native endian representation. Also, the underlying char encoding is
> - assumed to match ASCII in the range 0-0x7f.
> -</li>
> -<li>In the next iteration of locale support, I plan to add support for
> - (at least some) other multibyte encodings.
> -</li>
> -</ol>
> -<u>locale support</u><br>
> -<ol>
> -<li>The target for support is SUSv3 locale functionality. While nl_langinfo
> - has been extended, similar to glibc, it only returns values for related
> - locale entries.
> -</li>
> -<li>Currently, all SUSv3 libc locale functionality should be implemented
> - except for wcsftime and collating item support in regex.
> -</li>
> -</ol>
> -<u>stdio</u><br>
> -<ol>
> -<li>Conversion of large magnitude floating-point values by printf suffers a loss
> - of precision due to the algorithm used.
> -</li><br>
> -<li>uClibc's printf is much stricter than glibcs, especially regarding positional
> - args. The entire format string is parsed first and an error is returned if
> - a problem is detected. In locales other than C, the format string is checked
> - to be a valid multibyte sequence as well. Also, currently at most 10 positional
> - args are allowed (although this is configurable).
> -</li><br>
> -<li>BUFSIZ is configurable, but no attempt is made at automatic tuning of internal
> - buffer sizes for stdio streams. In fact, the stdio code in general sacrifices
> - sophistication/performace for minimal size.
> -</li><br>
> -<li>uClibc allows glibc-like custom printf functions. However, while not
> - currently checked, the specifier must be <= 0x7f.
> -</li><br>
> -<li>uClibc allows glibc-like custom streams. However, no in-buffer seeking is
> - done.
> -</li><br>
> -<li>The functions fcloseall() and __fpending() can behave differently than their
> - glibc counterparts.
> -</li><br>
> -<li>uClibc's setvbuf is more restrictive about when it can be called than glibc's
> - is. The standards specify that setvbuf must occur before any other operations
> - take place on the stream.
> -</li><br>
> -<li>Right now, %m is not handled properly by printf when the format uses positional
> - args.
> -</li><br>
> -<li>The FILEs created by glibc's fmemopen(), open_memstream(), and fopencookie()
> - are not capable of wide orientation. The corresponding uClibc routines do
> - not have this limitation.
> -</li><br>
> -<li>For scanf, the C99 standard states "The fscanf function returns the value of
> - the macro EOF if an input failure occurs before any conversion." But glibc's
> - scanf does not respect conversions for which assignment was surpressed, even
> - though the standard states that the value is converted but not stored.
> -</li></ol><br>
> -<hr><h3>Glibc bugs</h3><br>
> -glibc bugs that Ulrich Drepper has refused to acknowledge or comment on
> - ( <a href="http://sources.redhat.com/ml/libc-alpha/2003-09/">http://sources.redhat.com/ml/libc-alpha/2003-09/</a> )
> -<br>
> -<ol>
> -<li>The C99 standard says that for printf, a %s conversion makes no special
> - provisions for multibyte characters. SUSv3 is even more clear, stating
> - that bytes are written and a specified precision is in bytes. Yet glibc
> - treats the arg as a multibyte string when a precision is specified and
> - not otherwise.
> -</li><br>
> -<li>Both C99 and C89 state that the %c conversion for scanf reads the exact
> - number of bytes specified by the optional field width (or 1 if not specified).
> - uClibc complies with the standard. There is an argument that perhaps the
> - specified width should be treated as an upper bound, based on some historical
> - use. However, such behavior should be mentioned in the Conformance document.
> -</li><br>
> -<li>glibc's scanf is broken regarding some numeric patterns. Some invalid
> - strings are accepted as valid ("0x.p", "1e", digit grouped strings).
> - In spite of my posting examples clearly illustrating the bugs, they remain
> - unacknowledged by the glibc developers.
> -</li><br>
> -<li>glibc's scanf seems to require a 'p' exponent for hexadecimal float strings.
> - According to the standard, this is optional.
> -</li><br>
> -<li>C99 requires that once an EOF is encountered, the stream should be treated
> - as if at end-of-file even if more data becomes available. Further reading
> - can be attempted by clearing the EOF flag though, via clearerr() or a file
> - positioning function. For details concerning the original change, see
> - Defect Report #141. glibc is currently non-compliant, and the developers
> - did not comment when I asked for their official position on this issue.
> -</li><br>
> -<li>glibc's collation routines and/or localedef are broken regarding implicit
> - and explicit UNDEFINED rules.
> -</li><br></ol>
> -More to follow as I think of it...
> -<br><br><hr>
> -<h3>Profiling:</h3>
> -<p>
> -uClibc no longer supports 'gcc -fprofile-arcs -pg' style profiling, which
> -causes your application to generate a 'gmon.out' file that can then be analyzed
> -by 'gprof'. Not only does this require explicit extra support in uClibc, it
> -requires that you rebuild everything with profiling support. There is both a
> -size and performance penalty to profiling your applications this way, as well
> -as Heisenberg effects, where the act of measuring changes what is measured.
> -</p>
> -<p>
> -There exist a number of less invasive alternatives that do not require you to
> -specially instrument your application, and recompile and relink everything.
> -</p><p>
> -The OProfile system-wide profiler is an excellent alternative:
> - <a href="http://oprofile.sourceforge.net/">http://oprofile.sourceforge.net/</a>
> -</p><p>
> -Many people have had good results using the combination of Valgrind
> -to generate profiling information and KCachegrind for analysis:
> - <a href="http://developer.kde.org/~sewardj/">http://developer.kde.org/~sewardj/</a>
> - <a href="http://kcachegrind.sourceforge.net/">http://kcachegrind.sourceforge.net/</a>
> -</p><p>
> -Prospect is another alternative based on OProfile:
> - <a href="http://prospect.sourceforge.net/">http://prospect.sourceforge.net/</a>
> -</p><p>
> -And the Linux Trace Toolkit (LTT) is also a fine tool:
> - <a href="http://www.opersys.com/LTT/">http://www.opersys.com/LTT/</a>
> -</p><p>
> -FunctionCheck:
> - <a href="http://www710.univ-lyon1.fr/~yperret/fnccheck/">http://www710.univ-lyon1.fr/~yperret/fnccheck/</a>
> -</p>
> -
> -<!--#include file="footer.html" -->
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire at gmail.com>
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