Serial- / Socket IO and GCC nothrow attribute - c

Question

I have functions which abstract serial- and socket IO (Linux / Windows) implemented in C.
All of them are marked as extern "C" because they may get called from C++ as well.
Is it safe to use __attribute__((__nothrow__)) (or MinGW Macro __MINGW_NOTHROW) here / can i assume no exceptions are thrown?
Called functions - Sockets:
(not all additions for WinSock listed)
socket
connect
send / recv
close (closesocket on Windows)
sendto / recvfrom
Called functions - Serial:
Since serial IO code differs to much between windows / linux not all are listed here
Linux (GNU)
open
tcgetattr
read / write
close
Windows (MinGW)
CreateFile
GetCommState / SetCommTimeouts
ReadFile / WriteFile
CloseHandle
Since ANSI C has no exceptions (please correct me if I'm wrong) they won't be thrown, but how about GCC extensions and OS API calls?
Documentation: http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html (see nothrow).

Answer 1

C
GNU C (Linux) uses __THROW macro instead of __MINGW_NOTHROW.
While the MinGW one is __nothrow__ attribute only, __THROW contains __leaf__ attribute too.
C++
If you use C++, __THROW has another meaning: throw() - indicating that no exception is thrown (analog to __nothrow__; but defined in the C++ standard).
So it depends on whether you compile with C or C++, not on what you call the functions from (GNU C / C++ only!).
Example:
void f() __THROW;
Treated as ...
GNU C:
void f() __attribute__((__nothrow__, __leaf__))
GNU C++:
void f() throw()
Functions1) which are cancellation points, therefore not marked with
__THROW:
open()
read()
write()
close()
connect()
send()
recv()
close()
sendto()
recvfrom()
Functions1) marked with __THROW:
tcgetattr()
socket()
At least, these are save to __nothrow__.
In contrast, MinGW doesn't differ C from C++; in both cases the attribute is set.
Using example from above, __nothrow__ is set on C and C++:
void f() __attribute((__nothrow__))
Functions1) not marked with __MINGW_NOTHROW:
socket()
connect()
send()
recv()
closesocket()
sendto()
recvfrom()
CreateFile()
GetCommState()
SetCommTimeouts()
ReadFile()
WriteFile()
CloseHandle()
To make it short: none!
Compatibility
With C
C language code that is expecting to interoperate with C++ should be
compiled with -fexceptions. This will make debugging a C language
function called as part of C++-induced stack unwinding possible.
In particular, unwinding into a frame with no exception handling data
will cause a runtime abort. If the unwinder runs out of unwind info
before it finds a handler, std::terminate() is called.
Please note that most development environments should take care of
getting these details right. For GNU systems, all appropriate parts of
the GNU C library are already compiled with -fexceptions.
( source: http://gcc.gnu.org/onlinedocs/libstdc++/manual/using_exceptions.html )
So compiling with -fexceptions and there's no need for equivalent attribute. If you only can mark specific functions you have to / should use __nothrow__.
But while using __nothrow__ attribute looks save only on GNU C++, and some functions of GNU C on Linux, it's not that clear on Windows.
Addendum:
To avoid some parts of this problem, i've written a macro similar to __THROW but usable on MinGW too:
#if defined __GNUC__
#ifndef __THROW
#ifdef __cplusplus
#define __THROW throw()
#else
#define __THROW __attribute__((__nothrow__))
#endif
#endif
#else
#define __THROW
#endif
Note: __leaf__ is not included.
1) Talking only about those which are listed on my question.

Answer 2

take care of gcc version, nothrow has been introduced with gcc 3.3!
you can port __THROW from sys/cdefs.h to mingw:
/* skip this entire part on linux (= glibc available)*/
#if defined __GNUC__ && !defined __linux__
/********* port __GNUC_PREREQ macro to mingw *********/
# if !defined __GNUC_PREREQ
# if !defined __MINGW_H
# include <_mingw.h>
# define __GNUC_PREREQ(major, minor) __MINGW_GNUC_PREREQ(major, minor)
# else
# if defined (__GNUC_MINOR__)
# define __GNUC_PREREQ(major, minor) __GNUC__ > (major) || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))
# else
# define __GNUC_PREREQ(major, minor) 0
# endif
# endif
#endif /* __GNUC_PREREQ */
/********* from gnu c blirary *********/
/* All functions, except those with callbacks or those that
synchronize memory, are leaf functions. */
# if __GNUC_PREREQ (4, 6) && !defined _LIBC
# define __LEAF , __leaf__
# define __LEAF_ATTR __attribute__ ((__leaf__))
# else
# define __LEAF
# define __LEAF_ATTR
# endif
/* GCC can always grok prototypes. For C++ programs we add throw()
to help it optimize the function calls. But this works only with
gcc 2.8.x and egcs. For gcc 3.2 and up we even mark C functions
as non-throwing using a function attribute since programs can use
the -fexceptions options for C code as well. */
# if !defined __cplusplus && __GNUC_PREREQ (3, 3)
# define __THROW __attribute__ ((__nothrow__ __LEAF))
# define __THROWNL __attribute__ ((__nothrow__))
# define __NTH(fct) __attribute__ ((__nothrow__ __LEAF)) fct
# else
# if defined __cplusplus && __GNUC_PREREQ (2,8)
# define __THROW throw ()
# define __THROWNL throw ()
# define __NTH(fct) __LEAF_ATTR fct throw ()
# else
# define __THROW
# define __THROWNL
# define __NTH(fct) fct
# endif
# endif
#else /* Not GCC. */
# define __inline /* No inline functions. */
# define __THROW
# define __THROWNL
# define __NTH(fct) fct
#endif /* GCC. */
see glibc - sys/cdefs.h for full code.
edit: __GNUC_PREREQ can be replaced with __MINGW_GNUC_PREREQ(major, minor), then you don't have to redifine it as above.