Building a library with ffreestanding flag.

[hanseul1795]

Description

I'm trying a build a library with --ffreestanding flag on Android NDK r19c, and I'm getting use of undeclared identifier "LONG_BIT" error.

I know that (from #352), --ffreestanding

is the cause but it's a requirement for the library.

In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials\Engine\Tools\AndroidBuild\android-ndk-r19c\sources\android\cpufeatures\cpu-features.c:69:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\pthread.h:37:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\time.h:33:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\sys/time.h:37:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\sys/select.h:36:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\signal.h:37:
C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\bits/signal_types.h:65:53: error: use of undeclared identifier 'LONG_BIT'
typedef struct { unsigned long __bits[_KERNEL__NSIG/LONG_BIT]; } sigset64_t;
                                                    ^
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials\Engine\Tools\AndroidBuild\android-ndk-r19c\sources\android\cpufeatures\cpu-features.c:69:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\pthread.h:37:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\time.h:33:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\sys/time.h:37:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\sys/select.h:36:
In file included from C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\signal.h:203:
C:\Users\hanseul.shin\Desktop\PremakeTest\tutorials/Engine/Tools/AndroidBuild/android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\android/legacy_signal_inlines.h:71:33: error: use of undeclared identifier 'LONG_BIT'
  return (int)((local_set[bit / LONG_BIT] >> (bit % LONG_BIT)) & 1);

	.CFLAGS            	+  -m32 -target $NDKToolchainArmTarget$ -march=armv7-a -mfloat-abi=softfp -mcpu=cortex-a9 -mfpu=neon-vfpv4'
                        + ' -ffreestanding -fomit-frame-pointer'
	.Librarian         	= '$NDKToolchainClangRoot$\$NDKToolchainArmType$-ar.exe'
  	.Linker            	= '$NDKToolchainClangLinker$'
  	.Strip			   	= '$NDKToolchainClangRoot$\$NDKToolchainArmType$-strip.exe'
  	.ObjCopy		   	= '$NDKToolchainClangRoot$\$NDKToolchainArmType$-objcopy.exe'
  	.LinkerSystemPaths  = ' -Wl,--no-undefined -Wl,-z,noexecstack -Wl,-rpath-link=$NDKSysRoot$\usr\libs\$NDKToolchainArmType$\19'
						+ ' -Wl,-z,relro -Wl,-z,now -Wl,--fix-cortex-a8'
						+ '-target $NDKToolchainArmTarget$'
	.IncludePaths       + ' -I$NDKSysRoot$\usr\include\arm-linux-androideabi'
	.LinkerSystemLibs   + ' -lunwind'

I'm testing on API LEVEL = 19 and using llvm Clang toolchain with the right target.

Environment Details

Not all of these will be relevant to every bug, but please provide as much
information as you can.

• NDK Version: r19c
• Build system: Premake/FastBuild
• Host OS: Windows
• NDK API level: 19 (try to test below 21)

[enh-google]

you've given -ffreestanding to the compiler, which effectively says "i don't use the standard library", and then tried to use the standard library (specifically <signal.h>).

given that the library you're building here is Android's cpufeatures, i can tell you that that definitely doesn't need -ffreestanding, and -- as you've seen -- can't be built with -ffreestanding.

if you have other code which does need -ffreestanding, you'll have to build that separately.

[hanseul1795]

@enh-google
Thank you so much for the answer.

I was wondering, is there a case where -ffreestanding flag is absolutely required?

I have no clue why GCC did not complain about that flag but Clang did.

-ffreestanding flag definition is different in those compilers?

[enh-google]

the only time you need -ffreestanding is when you (a) can't call the C library or (b) don't even have a standard C library. the most common use is the kernel. the C library's startup code (which needs to avoid calling anything that isn't set up yet) is another case.

an Android app developer should never need -ffreestanding.