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IDProjectCategoryView StatusDate SubmittedLast Update
0008246CMakeCMakepublic2008-12-06 05:232008-12-16 09:33
ReporterMathieu Malaterre 
Assigned ToBrad King 
StatusclosedResolutionwon't fix 
PlatformOSOS Version
Product VersionCMake-2-6 
Target VersionFixed in Version 
Summary0008246: CHECK_FUNCTION_EXISTS and -Werror are incompatible with gcc builtins functions
DescriptionIf CFLAGS contains -Werror and checktestfunctionsexits test for a builtins function, cmake fails to determine if a function truly exist:

Run Build Command:/usr/bin/make "cmTryCompileExec/fast"
/usr/bin/make -f CMakeFiles/cmTryCompileExec.dir/build.make
make[1]: Entering directory
/usr/bin/cmake -E cmake_progress_report
/home/mmalaterre/Projects/gdcm/foo/CMakeFiles/CMakeTmp/CMakeFiles 1
Building C object CMakeFiles/cmTryCompileExec.dir/CheckFunctionExists.c.o
/usr/bin/gcc -Werror -DCHECK_FUNCTION_EXISTS=strncasecmp -o
CMakeFiles/cmTryCompileExec.dir/CheckFunctionExists.c.o -c
cc1: warnings being treated as errors
/usr/share/cmake-2.6/Modules/CheckFunctionExists.c:3: warning:
conflicting types for built-in function 'strncasecmp'
make[1]: *** [CMakeFiles/cmTryCompileExec.dir/CheckFunctionExists.c.o] Error 1
make[1]: Leaving directory
make: *** [cmTryCompileExec/fast] Error 2
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-  Notes
Mathieu Malaterre (developer)
2008-12-06 05:23

One possible solution would be to pass -fno-builtin to the cflags when gcc is detected.

           Don’t recognize built-in functions that do not begin with __builtin_ as prefix.

           GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to "alloca" may become single instructions that adjust the stack directly, and calls to "memcpy" may become
           inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the
           functions by linking with a different library. In addition, when a function is recognized as a built-in function, GCC may use information about that function to warn about problems with calls to that function, or to
           generate more efficient code, even if the resulting code still contains calls to that function. For example, warnings are given with -Wformat for bad calls to "printf", when "printf" is built in, and "strlen" is known
           not to modify global memory.

           With the -fno-builtin-function option only the built-in function function is disabled. function must not begin with __builtin_. If a function is named this is not built-in in this version of GCC, this option is
           ignored. There is no corresponding -fbuiltin-function option; if you wish to enable built-in functions selectively when using -fno-builtin or -ffreestanding, you may define macros such as:

                   #define abs(n) __builtin_abs ((n))
                   #define strcpy(d, s) __builtin_strcpy ((d), (s))
Brad King (manager)
2008-12-15 10:33

Does check_symbol_exists work?
Mathieu Malaterre (developer)
2008-12-15 10:46

Yes. Thanks.

$ export CFLAGS=-Werror
$ cmake .
-- Looking for strcasecmp
-- Looking for strcasecmp - found
Brad King (manager)
2008-12-16 09:33

I'd prefer not to mess with this. It should only be a problem for functions whose signatures are built in to the compiler. Further, I think check_symbol_exists is a better solution in pretty much all cases, so we can just leave check_function_exists as-is for compatibility.

- Issue History
Date Modified Username Field Change
2008-12-06 05:23 Mathieu Malaterre New Issue
2008-12-06 05:23 Mathieu Malaterre Note Added: 0014304
2008-12-15 10:05 Bill Hoffman Status new => assigned
2008-12-15 10:05 Bill Hoffman Assigned To => Brad King
2008-12-15 10:33 Brad King Note Added: 0014338
2008-12-15 10:46 Mathieu Malaterre Note Added: 0014339
2008-12-16 09:33 Brad King Note Added: 0014367
2008-12-16 09:33 Brad King Status assigned => closed
2008-12-16 09:33 Brad King Resolution open => won't fix

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