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Diffstat (limited to 'gcc/doc/standards.texi')
| -rw-r--r-- | gcc/doc/standards.texi | 38 |
1 files changed, 26 insertions, 12 deletions
diff --git a/gcc/doc/standards.texi b/gcc/doc/standards.texi index bbae350..011f7e2 100644 --- a/gcc/doc/standards.texi +++ b/gcc/doc/standards.texi @@ -152,7 +152,9 @@ library facilities: those in @code{<float.h>}, @code{<limits.h>}, @code{<iso646.h>}; since C99, also those in @code{<stdbool.h>} and @code{<stdint.h>}; and since C11, also those in @code{<stdalign.h>} and @code{<stdnoreturn.h>}. In addition, complex types, added in C99, are not -required for freestanding implementations. +required for freestanding implementations. Since C23, freestanding +implementations are required to support a larger range of library +facilities, including some functions from other headers. The standard also defines two environments for programs, a @dfn{freestanding environment}, required of all implementations and @@ -167,13 +169,13 @@ a program using the facilities of an operating system is an example of a program running in a hosted environment. @opindex ffreestanding -GCC aims towards being usable as a conforming freestanding -implementation, or as the compiler for a conforming hosted -implementation. By default, it acts as the compiler for a hosted +GCC aims towards being usable as the compiler for a conforming +freestanding or hosted implementation. +By default, it acts as the compiler for a hosted implementation, defining @code{__STDC_HOSTED__} as @code{1} and presuming that when the names of ISO C functions are used, they have -the semantics defined in the standard. To make it act as a conforming -freestanding implementation for a freestanding environment, use the +the semantics defined in the standard. To make it act as the compiler +for a freestanding environment, use the option @option{-ffreestanding}; it then defines @code{__STDC_HOSTED__} to @code{0} and does not make assumptions about the meanings of function names from the standard library, with exceptions @@ -181,12 +183,24 @@ noted below. To build an OS kernel, you may well still need to make your own arrangements for linking and startup. @xref{C Dialect Options,,Options Controlling C Dialect}. -GCC does not provide the library facilities required only of hosted -implementations, nor yet all the facilities required by C99 of -freestanding implementations on all platforms. -To use the facilities of a hosted -environment, you need to find them elsewhere (for example, in the -GNU C library). @xref{Standard Libraries,,Standard Libraries}. +GCC generally provides library facilities in headers that do not +declare functions with external linkage (which includes the headers +required by C11 and before to be provided by freestanding +implementations), but not those included in other headers. +Additionally, GCC provides @code{<stdatomic.h>}, even though it +declares some functions with external linkage (which are provided in +@code{libatomic}). On a few platforms, some of the headers not +declaring functions with external linkage are instead obtained from +the OS's C library, which may mean that they lack support for features +from more recent versions of the C standard that are supported in +GCC's own versions of those headers. On some platforms, GCC provides +@code{<tgmath.h>} (but this implementation does not support interfaces +added in C23). + +To use the facilities of a hosted environment, and some of the +facilities required in a freestanding environment by C23, you need to +find them elsewhere (for example, in the GNU C library). +@xref{Standard Libraries,,Standard Libraries}. Most of the compiler support routines used by GCC are present in @file{libgcc}, but there are a few exceptions. GCC requires the |