Re: [clisp-list] linux FFI: What/where is _IO_stdin/out/err_? -- errno

[Sam S. <sd...@gn...>]

> * In message <9F8582E37B2EE5498E76392AEDDCD3FE036C4ED4@G8PQD.blf01.telekom.de>
> * On the subject of "[clisp-list] linux FFI: What/where is _IO_stdin/out/err_? -- errno"
> * Sent on Fri, 4 Apr 2003 15:54:30 +0200
> * Honorable "Hoehle, Joerg-Cyril" <Joe...@t-...> writes:
>
> is it legal to assign to errno?
> E.g. errno = 0; in C application code?

yes, absolutely.

> Shall CLISP Linux FFI support assignment to errno?

yes, absolutely.

> On a (Suse)Linux box, I found
> /usr/include/errno.h
> /* Declare the `errno' variable, unless it's defined as a macro by
>    bits/errno.h.  This is the case in GNU, where it is a per-thread
>    variable.  This redeclaration using the macro still works, but it
> 
> And in /usr/include/bits/errno.h
> /* Function to get address of global `errno' variable.  */
> extern int *__errno_location (void) __THROW __attribute__ ((__const__));
> 
> #  if !defined _LIBC || defined _LIBC_REENTRANT
> /* When using threads, errno is a per-thread value.  */
> #   define errno (*__errno_location ())
> 
> Thus, printf("%d",errno); works.
> But such a #define does not work with errno=x;

why not?!

 (*foo()) = 10;

will write 10 into the memory area pointed to by the return value of
foo().

> BTW, in order not to have to revisit this area the day CLISP would
> have threads, linux:errno has to become a symbol-macro which expands
> to a FFI call. 
> (def-call-out __errno_location (:arguments) (:return-type (c-ptr int)))
> (define-symbol-macro errno (linux:__errno_location))
> But that does not support (setf linux:errno x).

se we should add a (setf linux:errno) macro or function.

-- 
Sam Steingold (http://www.podval.org/~sds) running RedHat8 GNU/Linux
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