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I'm using Xcode to prelink a collection of object files (*.o) and static libraries (*.a), all containing bitcode, into a single static library using Single-Object Prelinking.

In doing so, the resulting prelinked file does not contain bitcode.

The prelinking command and options emitted by Xcode looks like this:

ld -r -arch arm64 -bitcode_bundle -bitcode_verify -syslibroot
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.6.sdk 
a.o 
b.o 
...
x.a
y.a
-o libABC-arm64-master.o

The documentation for the bitcode_bundle option indicates that it "requires all the object files, static libraries and user frameworks/dylibs contain bit-code". I have used otool to verify that all of the constituent files contain bitcode.

No errors are raised or logged the by the ld command, even when I test it directly from the command line, separately from Xcode.

I'm stumped. And any help or suggestions would be appreciated.

Update: In further testing, I can create a prelinked file containing only any single .o file, and the final prelinked file WILL contain bitcode. However, including any two of those .o files, each of which contains bitcode, causes the prelinked file to contain NO bitcode.

Bill Hollings
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  • Have you tried the same process on slim objects with only a single arch? I remember Apple had a stance of not supporting fat libs at all some time ago. – Kikaxa Oct 18 '20 at 21:26
  • @Kikaxa Good suggestion. The latest code now generates single-arch files (actually XCFramework components), but the result is the same. The single-object prelink stage still seems to be interfering with bitcode. I'll edited the original question to remove references to fat files. – Bill Hollings Oct 18 '20 at 23:45

1 Answers1

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You probably should check for _LLVM section in the result library, not _bitcode:

otool -l lib.a | grep _LLVM

https://stackoverflow.com/a/33105733/13891048

Kikaxa
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  • Thanks. You are correct in that if I remove bitcode generation, there is no `__LLVM` section. Strange that on files that are _not_ prelinked, there are both `bitcode` and `__LLVM` sections. – Bill Hollings Oct 19 '20 at 15:12