llvm-ar does not generates symbol table for contained bitcode files

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1

Hi,

The behavior of llvm-ar appears to have changed such that the archive symbol table no longer contains symbols contained within bitcode modules in the archive. This behavior appears to have been changed with revision 184083 when the internal implementation of llvm-ar was changed from lib/Archive/Archive.cpp to lib/object/Archive.cpp. This seems to occur because ObjectFile::createObjectFile() does not support creating objects of bitcode type and thus llvm-ar cannot read them to retrieve the symbol information.

Is there a plan to add support back to llvm-ar to generate symbol table information when archiving bitcode files?

Thanks,
Jason

Steps to reproduce:
Create repro.c with the following contents:
const char* symbol = “Hello, World!”;

Create archive containing llvm bitcode files (no symbol table created):
clang -emit-llvm -c -o repro.bc repro.c
llvm-ar rs repro.a repro.bc

Create archive containing object files (symbol table is created):
clang -c -o repro.o repro.c
llvm-ar rs repro.a repro.o

2

Yes. I am sorry for the current state. Support for bitcode format will
be added back. The will be a few differences from before:

* It will use a "standard" symbol table instead of having a LLVM only
symbol table.
* The final name will be used. So on MachO you will see _foo, not foo.

In summary, the bitcode files in the .a archive will behave much more
like regular object files, making better suited for LTO.

Cheers,
Rafael

3

Hi Rafael,

Thank you for the response. The updated behavior to match the standard
symbol table makes sense.

Do you have any estimate for when the behavior describe below might be
implemented?

Thanks,
Jason

4

Sorry for not providing an estimate. There was a lot of yak shaving
needed and I was not sure how much. With r201881 llvm-ar should be
including IR files in the symbol table, but it is not using the
mangler yet, so the names will be wrong on OS X (missing a _ prefix).

I am currently working at second set of yak shaving needed to get the
mangler working in llvm-ar.

Cheers,
Rafael