176 lines
6.6 KiB
Plaintext
176 lines
6.6 KiB
Plaintext
Conformance of the GNU libc with various standards
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==================================================
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The GNU libc is designed to be conformant with existing standard as
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far as possible. To ensure this I've run various tests. The results
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are presented here.
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Open Group's hdrchk
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===================
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The hdrchk test suite is available from the Open Group at
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ftp://ftp.rdg.opengroup.org/pub/unsupported/stdtools/hdrchk/
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I've last run the suite on 2004-04-17 on a Linux/x86 system running
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a Fedora Core 2 test 2 + updates with the following results [*]:
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FIPS No reported problems
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POSIX90 No reported problems
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XPG3 Prototypes are now in the correct header file
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*** Starting unistd.h
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Missing: extern char * cuserid();
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Missing: extern int rename();
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*** Completed unistd.h
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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XPG4 Prototype is now in the correct header file
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and the _POSIX2_C_VERSION symbol has been removed
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*** Starting unistd.h
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Missing: extern char * cuserid();
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Missing: #define _POSIX2_C_VERSION (-1L)
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*** Completed unistd.h
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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POSIX96 Prototype moved
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(using "base realtime threads" subsets)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*** Starting unistd.h
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Missing: extern int pthread_atfork();
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*** Completed unistd.h
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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UNIX98 Prototypes moved and _POSIX2_C_VERSION removed
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(using "base realtime threads mse lfs" subset)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*** Starting unistd.h
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Missing: extern char * cuserid();
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Missing: #define _POSIX2_C_VERSION (-1L)
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Missing: extern int pthread_atfork();
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*** Completed unistd.h
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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That means all the reported issues are due to the headers having been
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cleaned up for recent POSIX/Unix specification versions. Duplicated
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prototypes have been removed and obsolete symbols have been removed.
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Which means that as far as the tests performed by the script go, the
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headers files comply to the current POSIX/Unix specification.
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[*] Since the scripts are not clever enough for the way gcc handles
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include files (namely, putting some of them in gcc-local directory) I
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copied over the iso646.h, float.h, and stddef.h headers and ignored the
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problems resulting from the split limits.h file).
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Technical C standards conformance issues in glibc
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=================================================
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If you compile programs against glibc with __STRICT_ANSI__ defined
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(as, for example, by gcc -ansi, gcc -std=c89, gcc -std=iso1990:199409
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or gcc -std=c99), and use only the headers specified by the version of
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the C standard chosen, glibc will attempt to conform to that version
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of the C standard (as indicated by __STDC_VERSION__):
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GCC options Standard version
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-ansi ISO/IEC 9899:1990
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-std=c89 ISO/IEC 9899:1990
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-std=iso9899:199409 ISO/IEC 9899:1990 as amended by Amd.1:1995
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-std=c99 ISO/IEC 9899:1999
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(Note that -std=c99 is not available in GCC 2.95.2, and that no
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version of GCC presently existing implements the full C99 standard.)
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You may then define additional feature test macros to enable the
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features from other standards, and use the headers defined in those
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standards (for example, defining _POSIX_C_SOURCE to be 199506L to
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enable features from ISO/IEC 9945-1:1996).
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There are some technical ways in which glibc is known not to conform
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to the supported versions of the C standard, as detailed below. Some
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of these relate to defects in the standard that are expected to be
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fixed, or to compiler limitations.
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Defects in the C99 standard
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===========================
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Some defects in C99 were corrected in Technical Corrigendum 1 to that
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standard. glibc follows the corrected specification.
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Implementation of library functions
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===================================
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The implementation of some library functions does not fully follow the
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standard specification:
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C99 added additional forms of floating point constants (hexadecimal
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constants, NaNs and infinities) to be recognised by strtod() and
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scanf(). The effect is to change the behavior of some strictly
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conforming C90 programs; glibc implements the C99 versions only
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irrespective of the standard version selected.
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C99 added %a as another scanf format specifier for floating point
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values. This conflicts with the glibc extension where %as, %a[ and
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%aS mean to allocate the string for the data read. A strictly
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conforming C99 program using %as, %a[ or %aS in a scanf format string
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will misbehave under glibc.
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Compiler limitations
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====================
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The macros __STDC_IEC_559__, __STDC_IEC_559_COMPLEX__ and
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__STDC_ISO_10646__ are properly supposed to be defined by the
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compiler, and to be constant throughout the translation unit (before
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and after any library headers are included). However, they mainly
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relate to library features, and the necessary magic has yet to be
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implemented for GCC to predefine them to the correct values for the
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library in use, so glibc defines them in <features.h>. Programs that
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test them before including any standard headers may misbehave.
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GCC doesn't support the optional imaginary types. Nor does it
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understand the keyword _Complex before GCC 3.0. This has the
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corresponding impact on the relevant headers.
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glibc's use of extern inline conflicts with C99: in C99, extern inline
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means that an external definition is generated as well as possibly an
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inline definition, but in GCC it means that no external definition is
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generated. When GCC's C99 mode implements C99 inline semantics, this
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will break the uses of extern inline in glibc's headers. (Actually,
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glibc uses `extern __inline', which is beyond the scope of the
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standard, but it would clearly be very confusing for `__inline' and
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plain `inline' to have different meanings in C99 mode.)
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glibc's <tgmath.h> implementation is arcane but thought to work
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correctly; a clean and comprehensible version requires compiler
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builtins.
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For most of the headers required of freestanding implementations,
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glibc relies on GCC to provide correct versions. (At present, glibc
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provides <stdint.h>, and GCC doesn't.)
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Implementing MATH_ERRNO, MATH_ERREXCEPT and math_errhandling in
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<math.h> needs compiler support: see
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http://sources.redhat.com/ml/libc-hacker/2000-06/msg00008.html
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http://sources.redhat.com/ml/libc-hacker/2000-06/msg00014.html
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http://sources.redhat.com/ml/libc-hacker/2000-06/msg00015.html
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Issues with headers
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===================
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None known.
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