freestanding implementation for a freestanding environment, use the
option @option{-ffreestanding}; it will then define
@code{__STDC_HOSTED__} to @code{0} and not make assumptions about the
-meanings of function names from the standard library. 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}.
+meanings of function names from the standard library, with exceptions
+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
environment, you will 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
+freestanding environment provide @code{memcpy}, @code{memmove},
+@code{memset} and @code{memcmp}. Some older ports of GCC are
+configured to use the BSD @code{bcopy}, @code{bzero} and @code{bcmp}
+functions instead, but this is deprecated for new ports.
+Finally, if @code{__builtin_trap} is used, and the target does
+not implement the @code{trap} pattern, then GCC will emit a call
+to @code{abort}.
+
For references to Technical Corrigenda, Rationale documents and
information concerning the history of C that is available online, see
@uref{http://gcc.gnu.org/readings.html}