Running ./configure with -Wall leads to libraries not being found

Question

I'd like to use -Wall and -Werror as flags for gcc in an autotools project, but I don't want to put them in my configure.ac.

As such, I tried using ./configure CFLAGS='-Wall -Werror', only to get an error from one of my AC_SEARCH_LIBS macro calls:

AC_SEARCH_LIBS([pow], [m], , AC_MSG_ERROR([Could not find standard math library.]))

Resulting error when running configure with the CFLAGS added:

configure: error: Could not find standard math library.

What am I doing wrong here? Configuration works fine without the CFLAGS variable set.

Check your config log file for the output that came from it trying to run that step. You'll see what the error was and can probably fix it. — Carl Norum
The log file tells me: error: conflicting types for built-in function 'pow' [-Werror], after trying to compile conftest.c. Removing -Werror from the CFLAGS gets rid of the issue, but that's not really any use to me. — heuristicus
permalink.gmane.org/gmane.comp.sysutils.autoconf.patches/5791 — William Pursell
So fix the prototype to match in whatever hike generates it, and then try again. — Carl Norum
@Carl You cannot do that. This is a known issue; the tests that autoconf uses typically compile with warnings, and elevating warnings to errors via -Werror will cause the tests to fail. A reasonable way to deal with this (if using automake) is to conditionally add the flags to AM_CFLAGS (the condition being a configure time check that CC accepts the flags). — William Pursell

Jack Kelly Jack Kelly · Accepted Answer · 2013-01-11T22:56:03

As you now know, elevating the compile warnings to errors confuses ./configure.

What you can do is pass custom CFLAGS at make time:

$ ./configure
$ make CFLAGS='-O2 -g -Wall -Wextra -Werror'

The other option is William Pursell's approach: add an option to ./configure to turn on -Werror if supported:

(configure.ac)

AC_ARG_ENABLE([werror],
              [AS_HELP_STRING([--enable-werror], [Use -Werror @<:@no@:>@])],
              [:],
              [enable_werror=no])
AM_CONDITIONAL([ENABLE_WERROR], [test "$enable_werror" = yes])

(Makefile.am)

if ENABLE_WERROR
AM_CFLAGS += -Werror
endif

Running ./configure with -Wall leads to libraries not being found

1 Answers