Unrecognized option -mbig-obj

[Kaaserne]

The docs says:

---

Portability

The library is highly portable and relies only on a small set of C++11 features:

• variadic templates
• type traits
• rvalue references
• decltype
• trailing return types
• deleted functions
• alias templates

These are available since GCC 4.8, Clang 3.0 and MSVC 19.0 (2015). For older compilers use {fmt} version 4.x which continues to be maintained and only requires C++98.

---

If you mean GCC 4.8.0, I think this is a small mistake because the library is not able to build because GCC 4.8.0 does not support method ref qualifiers (on line 831 format.h):

Compiler	rvalue refs	ref-qualifiers	source
GCC	4.3	4.8.1	here
Clang	2.9	2.9	here
Intel	12.0	14.0	here
Visual C++	VC10	Nov 2013 CTP	here

---

With GCC 4.8.1 installed however, building on Windows 10 with x86_64-4.8.1-release-posix-seh-rt_v3-rev2 gives:

c:/users/marcd/downloads/x86_64-4.8.1-release-posix-seh-rt_v3-rev2/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/4.8.1/../../../../x86_64-w64-mingw32/bin/as.exe: unrecognized option `-mbig-obj'
mingw32-make.exe[3]: *** [fmt/CMakeFiles/fmt.dir/src/os.cc.obj] Error 1
mingw32-make.exe[3]: *** Waiting for unfinished jobs....
fmt\CMakeFiles\fmt.dir\build.make:96: recipe for target 'fmt/CMakeFiles/fmt.dir/src/os.cc.obj' failed
c:/users/marcd/downloads/x86_64-4.8.1-release-posix-seh-rt_v3-rev2/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/4.8.1/../../../../x86_64-w64-mingw32/bin/as.exe: unrecognized option `-mbig-obj'
mingw32-make.exe[3]: *** [fmt/CMakeFiles/fmt.dir/src/format.cc.obj] Error 1
mingw32-make.exe[2]: *** [fmt/CMakeFiles/fmt.dir/all] Error 2
mingw32-make.exe[1]: *** [CMakeFiles/untitled.dir/rule] Error 2
mingw32-make.exe: *** [untitled] Error 2
fmt\CMakeFiles\fmt.dir\build.make:82: recipe for target 'fmt/CMakeFiles/fmt.dir/src/format.cc.obj' failed
CMakeFiles\Makefile2:141: recipe for target 'fmt/CMakeFiles/fmt.dir/all' failed
CMakeFiles\Makefile2:121: recipe for target 'CMakeFiles/untitled.dir/rule' failed
Makefile:137: recipe for target 'untitled' failed

Main.cpp:

#include <fmt/core.h>

int main() {
    fmt::print("The answer is {}", 42);
    return 0;
}

Cmake:

cmake_minimum_required(VERSION 3.17)
project(untitled)

add_subdirectory(fmt)

add_executable(untitled main.cpp)
target_link_libraries(${PROJECT_NAME} PRIVATE fmt::fmt)

Am I missing something?

[vitaut]

the library is not able to build because GCC 4.8.0 does not support method ref qualifiers (on line 831 format.h)

Those qualifiers are non-essential, a PR to remove them is welcome. Alternatively you can use GCC 4.8.1.

-mbig-obj was introduced in 47ae521 to workaround a bug in mingw. I think the solution is to detect flag support with check_cxx_compiler_flag. Again a PR would be welcome because you are in the best position to check if it works.

[Kaaserne]

Alright I'll try and make a PR soon. I'm busy this week but you will receive it somewhere soon hopefully.

[Kaaserne]

While this issue is open anyway, I had another question regarding the insertion of the flag -fPIC. One of my builds errored because of a missing -fPIC flag in GCC 4.8:

/usr/bin/ld: /home/runner/work/cpp-lazy/cpp-lazy/build/prefix/lib/libfmt.a(format.cc.o): relocation R_X86_64_32S against symbol `_ZTVN3fmt2v712format_errorE' can not be used when making a PIE object; recompile with -fPIC

As one of my contributors (@friendlyanon) mentioned:

Regarding -fPIC, since {fmt} does not define library type, that add_library call is affected by BUILD_SHARED_LIBS's value, which by default is not defined, hence false, ie {fmt} is built as a static library as evident by the fmt.a artifact name.
Your library is explicitly defined as INTERFACE (usage requirements only) and for the tests it's consumed directly using an executable target.
Indeed, this doesn't make much sense.

Are we missing something here?

[vitaut]

Not sure what's the question, -fPIC is added when BUILD_SHARED_LIBS is ON.

[Kaaserne]

If I understood correctly, this variable is simply set to its initial value, so false. But when importing fmt the following way:

option(CPP-LAZY_USE_INSTALLED_FMT "Import {fmt} using find_package" NO)
if(CPP-LAZY_USE_INSTALLED_FMT)
    find_package(fmt 7 REQUIRED CONFIG)
else()
    set(FMT_INSTALL YES CACHE INTERNAL "" FORCE)
    set(FMT_OS YES CACHE INTERNAL "")
    include(FetchContent)
    FetchContent_Declare(fmt
            GIT_REPOSITORY https://github.com/fmtlib/fmt.git
            GIT_TAG a581e9e5d83673fefbecb7cc6ea2514af83f77c8
            UPDATE_DISCONNECTED YES)
    FetchContent_MakeAvailable(fmt)
endif()

target_link_libraries(cpp-lazy INTERFACE fmt::fmt)

But that gives this link error on GCC 4.8, so I was wondering if you had any pointers

[vitaut]

Closing as the original issue has been fixed (thanks for providing the fix). As for -fPIC, I suggest opening a separate issue if it's more than just a problem of building with inconsistent CMake flags.