How to check a static library is built contain bitcode?

Question

I have a static library that is built by other company. I want to know if it's a static library containing bitcode, which command can detect it in terminal?

Krick

Answer 1

As it was alread written in other answers,

otool -l yourlib.a | grep __LLVM

is the way to go.

An Apple engineer says using

otool -l yourlib.a | grep bitcode

is not reliable.

Searching for a "bitcode" section is not a reliable way to detect if your files contain embedded bitcode. If you want to do that, search for the "__LLVM" segment. You should be aware that a normal build with the -fembed-bitcode-marker option will produce minimal size embedded bitcode sections without any real content. This is done as a way of testing the bitcode-related aspects of your build without slowing down the build process. The actual bitcode content is included when you do an Archive build.

See also the comments by xCocoa.

It seems, that otool does not report the bitcode if code for the iPhone Simulator's architecture is included (x86_64 or i386).

You can list the lib's architectures with:

lipo -info yourlib.a

Then you can check for bitcode for each architecture separately, e.g:

otool -arch armv7 -l yourlib.a  | grep bitcode
otool -arch arm64 -l yourlib.a  | grep bitcode

Tabret

Is the following correct: if static library was not build with ENABLE_BITCODE=NO it cannot be used from target which has ENABLE_BITCODE=YES? Is opposite correct too? – Subaltern

@EugeneDubinin Bitcode is just some extra information, so having it does no harm besides a slightly increased size. However, the lack of bitcode in the binary means you can't link it against a target that requires bitcode (i.e. bitcode is enabled). – Merritt

Be aware that if you compile with -fembed-bitcode-marker and not -fembed-bitcode (inspect your compiler output), you may get a false positive with these commands, as the bitcode "marker" is present, just not the actual bitcode. This answer has more info on that. – Evolutionary

Following up on @WilliamDenniss's answer you can check for the false positive by grepping for bitcode in the otool results and then looking at the size field 4 lines after that. (you can use the -A 4 parameter to see the next 4 lines after the grep match) If the size is 1 then it means that -fembed-bitcode was not set and the library does not contain bitcode. – Trahan

Answer 2

It is recommended to test against LLVM symbols:

otool -l yourlib.a | grep LLVM

You should get some lines with "__LLVM"

Expressly

I try it,but not found anything,the yourlib.a is contain bitcode,i'm sure. – Krick

Have you build for Archive? – Expressly

Could you please indicate the source of your claim? Why should I grep for LLVM? – Selden

See this answer regarding searching for "__LLVM". – Kamila

Answer 3

Disclaimer: I'm the author of LibEBC.

You can use ebcutil to see whether bitcode is present in a Mach-O binary or library. You can even use it to extract the embedded bitcode from it.

https://github.com/JDevlieghere/LibEBC

Susurrate

I tried using the library but on the latest macOS, it doesn't seem to compile at all. – Jugendstil

Feel free to open an issue on GitHub. – Susurrate

Answer 4

And if you want to check if a specific file (yourFile.o) in the static library is bitcode enabled, you can extract the 'staticLibrary.a' and use the same otool command. However macOS doesn't allow to extract your staticLibrary.a at times with the default extract utility and most 3rd party tools doesn't work either.

You can follow these steps to check specific .o files

1. Get the info of the architecture

   lipo -info yourStaticLibrary.a
   

eg output: armv7 arm64

2. Extract yourStaticLibrary.a for any or both of the above architecture

   lipo yourStaticLibrary.a -thin armv7 -output yourStaticLibraryarmv7.a
   

(specify the output path you want to extract to)

3. You get the 'yourStaticLibraryarmv7.a' which then can be easily extracted with the default mac unarchiver

4. On extracting, you then get a folder 'yourStaticLibraryarmv7' containing all the .o files

5. otool -l yourFile.o | grep bitcode or with the specific architecture

   otool -arch armv7 -l yourFile.o  | grep bitcode
   

If the file is bitcode enabled , you get 'sectname __bitcode' in the commandline

Centesimo

the default mac unarchiver was giving me grief, so you can try this command ar -t yourStaticLibraryarmv7.a to see the list of .o files, and ar -xv yourStaticLibraryarmv7.a yourFile.o – Riesling

@Riesling That doesn't work for me I get ar:***.a: Inappropriate file type or format when running ar -t ***.a, I followed instructions to remove the armv7 slice as stated in the answer – Escalator

1. lipo -info lib.a 2. Check architectures, select your architecture 3. lipo lib.a -thin arm64 -output lib_arm64.a 4. ar -tv lib_arm64.a // List the files 5. ar -xv lib_arm64.a yourfile.o // File extracted 6. otool -arch armm64 -l yourfile.o | grep bitcode If the file is bitcode enabled , you get 'sectname __bitcode' in the commandline – Foucquet

Answer 5

1. lipo -info lib.a // Your static library
2. Check architectures, select your architecture
3. lipo lib.a -thin arm64 -output lib_arm64.a // Extract your architecture
4. ar -tv lib_arm64.a // List the files
5. ar -xv lib_arm64.a yourfile.o // File extracted
6. otool -arch armm64 -l yourfile.o | grep bitcode

If the file is bitcode enabled, you get 'sectname __bitcode'

Foucquet