[PATCH] cmake: workaround GCC 7.2 segfault on v?sn?printf

[Alexander Turenko]

Fixed Ubuntu Artful:

```
diff --git a/cmake/compiler.cmake b/cmake/compiler.cmake
index b471b0c38..0d7bf6347 100644
--- a/cmake/compiler.cmake
+++ b/cmake/compiler.cmake
@@ -350,14 +350,14 @@ endif()
 # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83448

 # It is important for the test case to be compiled w/o any extra
-# flags and with -O2. Say, -Wall allows the case be compiled
-# successfully on gcc-7.2.1.
+# flags and with -O2. Say, -Wformat allows the case be compiled
+# successfully on gcc-7.2.
 set(PREVIOUS_CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
 set(CMAKE_C_FLAGS "")
 set(CMAKE_REQUIRED_DEFINITIONS "")
 set(CMAKE_REQUIRED_INCLUDES "")
 set(CMAKE_REQUIRED_LIBRARIES "")
-set(CMAKE_REQUIRED_FLAGS "-O2")
+set(CMAKE_REQUIRED_FLAGS "-O2 -Wno-format")

 check_c_source_compiles("
 char *a;
```

https://travis-ci.org/tarantool/tarantool/builds/472898526

WBR, Alexander Turenko.

On Fri, Dec 28, 2018 at 07:48:54AM +0300, Alexander Turenko wrote:
> GCC 7.2.1 fails like so on our codebase:
> 
> /tarantool/src/lib/json/json.c: In function ‘json_token_snprint’:
> /tarantool/src/lib/json/json.c:324:1: internal compiler error: Segmentation fault
>  json_token_snprint(char *buf, int size, const struct json_token *token,
>  ^~~~~~~~~~~~~~~~~~
> 
> The backtrace of cc1 is the following (failed to install compatible
> debuginfo on Fedora 26, so ??s):
> 
>     #0  0x0000000000d0320c in get_source_location_for_substring(cpp_reader*, string_concat_db*, unsigned int, cpp_ttype, int, int, int, unsigned int*) ()
>     #1  0x00000000005c0e79 in c_get_substring_location(substring_loc const&, unsigned int*) ()
>     #2  0x00000000007f8418 in format_warning_va(substring_loc const&, source_range const*, char const*, int, char const*, __va_list_tag (*) [1]) ()
>     #3  0x00000000007f838b in format_warning_at_substring(substring_loc const&, source_range const*, char const*, int, char const*, ...) ()
>     #4  0x0000000000c72c2d in ?? ()
>     #5  0x0000000000f6f308 in execute_one_pass(opt_pass*) ()
>     #6  0x0000000000787da6 in ?? ()
>     #7  0x00000000012ac338 in symbol_table::compile() ()
>     #8  0x0000000000de650f in symbol_table::finalize_compilation_unit() ()
>     #9  0x00000000012ee8df in ?? ()
>     #10 0x0000000000d3ba84 in toplev::main(int, char**) ()
>     #11 0x0000000000d3d35b in main ()
> 
> The issue in the GCC bugtracker: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83448
> 
> The idea of the commit is to check builtin snprintf with the code from
> GCC test suite and disable all related builtins if the compiler is GCC
> and the case fails.
> 
> We also need to disable FORTIFY_SOURCES in the case, because it uses
> v?sn?printf builtins directly.
> ---
> 
> no issue
> https://github.com/tarantool/tarantool/tree/Totktonada/workaround-gcc-7.2-snprintf-segfault
> 
> Be attentive: I pushed DO NOT MERGE commit upward the commit I send here
> to enable full testing on the bugfix branch: [1] (hope it will pass).
> The topmost commit should NOT be pushed to 2.1.
> 
> [1]: https://travis-ci.org/tarantool/tarantool/builds/472881226
> 
>  cmake/compiler.cmake | 43 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/cmake/compiler.cmake b/cmake/compiler.cmake
> index 4062d13ec..b471b0c38 100644
> --- a/cmake/compiler.cmake
> +++ b/cmake/compiler.cmake
> @@ -333,6 +333,8 @@ if (NOT HAVE_BUILTIN_CTZ OR NOT HAVE_BUILTIN_CTZLL)
>              HAVE_FFSL)
>          check_c_source_compiles("#include <string.h>\n#include <strings.h>\nint main(void) { return ffsll(0UL); }"
>              HAVE_FFSLL)
> +        set(CMAKE_REQUIRED_FLAGS "")
> +        set(CMAKE_REQUIRED_DEFINITIONS "")
>      endif()
>  endif()
>  
> @@ -343,3 +345,44 @@ else()
>      set(CMAKE_HOST_C_COMPILER ${CMAKE_C_COMPILER})
>      set(CMAKE_HOST_CXX_COMPILER ${CMAKE_CXX_COMPILER})
>  endif()
> +
> +# Check for broken __builtin_v?sn?printf() in gcc-7.2.
> +# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83448
> +
> +# It is important for the test case to be compiled w/o any extra
> +# flags and with -O2. Say, -Wall allows the case be compiled
> +# successfully on gcc-7.2.1.
> +set(PREVIOUS_CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
> +set(CMAKE_C_FLAGS "")
> +set(CMAKE_REQUIRED_DEFINITIONS "")
> +set(CMAKE_REQUIRED_INCLUDES "")
> +set(CMAKE_REQUIRED_LIBRARIES "")
> +set(CMAKE_REQUIRED_FLAGS "-O2")
> +
> +check_c_source_compiles("
> +char *a;
> +int b;
> +
> +int
> +main(void)
> +{
> +    for (;;) {
> +        if (b < 0)
> +            main();
> +        __builtin_snprintf(a, b, \"%*s\", b, \"\");
> +    }
> +    return 0;
> +}" HAVE_BUILTIN_SNPRINTF)
> +
> +set(CMAKE_REQUIRED_FLAGS "")
> +set(CMAKE_C_FLAGS ${PREVIOUS_CMAKE_C_FLAGS})
> +
> +# /usr/include/stdio.h (bits/stdio2.h to be exact) uses builtin
> +# gcc v?sn?printf functions when fortify source is enabled.
> +if (CMAKE_COMPILER_IS_GNUCC AND NOT HAVE_BUILTIN_SNPRINTF)
> +    add_compile_flags("C;CXX" "-Wp,-U_FORTIFY_SOURCE")
> +    add_compile_flags("C;CXX" "-fno-builtin-sprintf")
> +    add_compile_flags("C;CXX" "-fno-builtin-snprintf")
> +    add_compile_flags("C;CXX" "-fno-builtin-vsnprintf")
> +    add_compile_flags("C;CXX" "-fno-builtin-vsprintf")
> +endif()
> -- 
> 2.20.1
>