Zack Weinberg <zackw@xxxxxxxxx> writes: > On Wed, Jan 24, 2018 at 6:55 PM, Zack Weinberg <zackw@xxxxxxxxx> wrote: > >> On Wed, Jan 24, 2018 at 4:36 PM, Ferenc Wágner <wferi@xxxxxxx> wrote: >> >>> Since ceil() can be inlined when optimization is enabled, I use >>> >>> AC_SEARCH_LIBS([ceil], [m], , [AC_MSG_ERROR([ceil not found])]) >>> AC_SUBST([m_LIBS], [$LIBS]) >>> >>> to link against libm only when necessary (that is, when ceil is not >>> inlined). However, it does not work because GCC says in config.log: >>> >>> conftest.c:76:6: warning: conflicting types for built-in function 'ceil' >>> char ceil (); >>> ~~~~ >>> >>> and inlining is disabled, thus ceil becomes an undefined reference >>> without -lm. However, in the actual code where math.h is #included, the >>> above warning does not happen, ceil is inlined and I unnecessarily link >>> with -lm. How could I overcome this? >> >> You could try setting -Wl,--as-needed (which really should be the >> default) in your makefiles. > > That was unnecessarily cryptic, sorry. Nevermind, it was fine, I met --as-needed before, but I was somewhat wary about using it for no concrete reason (FUD). > The GNU linker accepts an option --as-needed Which brings us to a followup question: how to check whether it's safe to use --as-needed? Is AX_CHECK_LINK_FLAG sufficient, should I check for the effect somehow or what else is the best practice here? > (This is not the default only for silly historical reasons which let's > not get into here.) Just out of curiosity, have to got a good link to the topic? -- Thanks, Feri _______________________________________________ Autoconf mailing list Autoconf@xxxxxxx https://lists.gnu.org/mailman/listinfo/autoconf
