On Mon, Mar 10, 2014 at 12:53 PM, Thomas Klausner <tk@xxxxxxxxxx> wrote: > On Sun, Mar 09, 2014 at 07:25:20PM -0400, Mike Frysinger wrote: >> On Sat 08 Mar 2014 22:30:59 Thomas Klausner wrote: >> > There is a bug in dlopen(3). The NOTES section claims: >> > >> > "The symbols RTLD_DEFAULT and RTLD_NEXT are defined by <dlfcn.h> only >> > when _GNU_SOURCE was defined before including it." >> > >> > However, this is not correct. >> > >> > From dlfcn.h on a "Gentoo Base System release 2.1": >> > #ifdef __USE_GNU >> > ... >> > # define RTLD_NEXT ((void *) -1l) >> > ... >> > # define RTLD_DEFAULT ((void *) 0) >> > ... >> > >> > You can verify this by compiling the attached program. For me it gives: >> > test.c: In function `main': >> > test.c:8: error: `RTLD_NEXT' undeclared (first use in this function) >> > test.c:8: error: (Each undeclared identifier is reported only once >> > test.c:8: error: for each function it appears in.) >> > >> > It works if I set "__USE_GNU_" instead. >> > >> > Please also check the "Glibc extensions: dladdr() and dlvsym()" >> > section, it also mentions _GNU_SOURCE. >> >> the man page is correct. you must define _GNU_SOURCE before including any >> headers. you must never use the __USE_XXX defines directly. >> >> see feature_test_macros(7) for details as the dlopen() man page references. > > Thanks for your reply. > > Michael Kerrisk already pointed me to that in a private email. Yup, though it was unintentional -- I overlooked that the fact that reply on my mobile device did not do a CC-all. Cheers, Michael > > However, this makes writing portable code a bit harder. When I know I need > the define for this particular header, I can wrap the header in > #define __FOO > #include foo.h > #undef __FOO > > but here it seems I have to live with whatever side effects __FOO > might have on any other headers. > > Well, you can't fix that, so thanks for the pointer. > Thomas -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
