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Re: Autoconf protype breaks GCC builtin inlining

From: Zack Weinberg
Subject: Re: Autoconf protype breaks GCC builtin inlining
Date: Wed, 24 Jan 2018 18:55:38 -0500

On Wed, Jan 24, 2018 at 4:36 PM, Ferenc Wágner <address@hidden> wrote:
> Hi,
> Since ceil() can be inlined when optimization is enabled, I use
> AC_SEARCH_LIBS([ceil], [m], , [AC_MSG_ERROR([ceil not found])])
> 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.


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