Hi Andy, Andy Wingo <wi...@pobox.com> writes:
> wingo pushed a commit to branch master > in repository guile. > > commit a396e14cb139eba37eeeea44e745bfc57bd1f37d > Author: Mark H Weaver <m...@netris.org> > Date: Tue Jan 5 16:30:41 2016 -0500 > > FFI: Add support for functions that set 'errno'. > > Implements wishlist item <https://debbugs.gnu.org/18592>. > Requested by Frank Terbeck <f...@bewatermyfriend.org>. > Based on a proposed patch by Nala Ginrut <nalagin...@gmail.com>. > Patch ported to 2.2 by Andy Wingo <wi...@pobox.com>. > > * libguile/foreign.c (cif_to_procedure): Add 'with_errno' argument. > If true, truncate result to only one return value. > (scm_i_foreign_call): Separate the arguments. Always return errno. If I understand correctly, this unconditionally clears 'errno' before every FFI call. In my original version of this patch for stable-2.0, I deliberately avoided modifying (or even accessing) 'errno' unless the user asked to do so. I would prefer to keep those semantics in 2.2. More generally, it seems to me that we should avoid mutating user-visible state when a clueful user would not expect it. I would certainly find it surprising for 'errno' to be modified when calling a C function that simply retrieves a field from a C struct, for example. What do you think? Thanks, Mark > @@ -1010,7 +1042,9 @@ scm_i_foreign_call (SCM foreign, const union > scm_vm_stack_element *argv) > max (sizeof (void *), cif->rtype->alignment)); > > /* off we go! */ > + errno = 0; > ffi_call (cif, func, rvalue, args); > + *errno_ret = errno; > > return pack (cif->rtype, rvalue, 1); > }
