doc snippets about defines we provide and/or use

1 files changed, 61 insertions, 0 deletions

diff --git a/docs/defines.txt b/docs/defines.txt
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+Feeble attempt to document the horde of #defines we deal with.
+Editors, plese make your descriptions short but informative.
+
+
+
+__BEGIN_DECLS, __END_DECLS
+    Defined to either empty or 'extern "C" {' and '}' if included by C++.
+
+__USE_GNU, __USE_BSD, __USE_XOPEN[2K], __USE_SVID, __USE_POSIX...
+    If defined, user program which included us requests compat additions
+    from relevant standard or Unix flavor. See features.h for full list.
+
+__USE_FILE_OFFSET64
+__USE_LARGEFILE[64]
+_LARGEFILE[64]_SOURCE
+_FILE_OFFSET_BITS
+    ???
+
+__NTH(fct)
+__THROW
+__REDIRECT(name, proto, alias)
+__REDIRECT_NTH(name, proto, alias)
+    ???
+
+__BIG_ENDIAN    4321
+__LITTLE_ENDIAN 1234
+    Should be always as shown. __PDP_ENDIAN is historic, ignore?
+__BYTE_ORDER, __FLOAT_WORD_ORDER
+    Should be defined to __BIG_ENDIAN or __LITTLE_ENDIAN.
+    Usage: "#if __BYTE_ORDER == __LITTLE_ENDIAN ..."
+    __USE_BSD adds versions without leading "__" for above four defines.
+_BIG_ENDIAN, __BIG_ENDIAN__
+_LITTLE_ENDIAN, __LITTLE_ENDIAN__
+    Defined (to what?) by gcc for some architectures to indicate endianness.
+    Seems that the fact of defined-ness is an indicator, not the value.
+
+__USE_EXTERN_INLINES
+    If defined, headers will supply some function as inlines.
+    uclibc itself is built with this option off and provides
+    out-of-line version of every inlined function in case user program
+    calls it instead of using an inline.
+_EXTERN_INLINE
+    Define it to replace "extern __inline" string in inline definitions
+    (those enabled by __USE_EXTERN_INLINES) with something else.
+    A few uclibc .c files use it to create non-inlined functions
+    by defining it to "".
+
+_LIBC
+UCLIBC_INTERNAL
+    Defined only at libc build time. _LIBC is probably from glibc,
+and UCLIBC_INTERNAL is added by vda (he didn't know about _LIBC).
+Both defines are physically deleted from headers (using unifdef tool)
+in installed headers ("make install").
+
+__UCLIBC_XXX
+    uclibc-internal and uclibc-specific defines. In particular:
+__UCLIBC_HAS_XXX__, __UCLIBC_HAVE_XXX__
+    __UCLIBC_HAS_XXX__ are booleans (defined/undefined), defined in
+    uClibc_config.h and generated from uclibc .config file.
+    __UCLIBC_HAVE_XXX__ are booleans from bits/uClibc_arch_features.h
+    (there are more __UCLIBC_XXX defines there)