llvm dev - Aug 2020 - Adding bitcode to an existing MachO object file

This is a silly question, but I am in a situation where I need to build x86
and arm assembly sources for some sources while the rest will be built with
C. I do know that just adding `-fembed-bitcode` to a C sources would embed
bitcode, but doing the same for the assembly files will not do that (at
least, it will add the 1-byte `_LLVM,__asm` section, but not the
`__LLVM,__bitcode` section). Furthermore, I do need the final output to
contain bitcode for all files used.

So, my question is if it is possible to add the `__LLVM,__bitcode` section
later to the MachO object file. I tried to archive the bitcode using `xar`
and run `llvm-objcopy main.o --add-section=__LLVM,__bitcode=main.xar
main2.o`, but it failed with an `unsupported load command`. This seems to
be the case for all usages of `llvm-objcopy` with MachO files.

Cheers and thanks

-- Joseph
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What version of llvm-objcopy are you using? I know it’s had many fixes for
Mach-O recently. If you’re running into a bug with the latest llvm-objcopy (from
the master branch), it’d be great if you could file a bug on bugs.llvm.org with
your input file (if possible).

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Joseph
via llvm-dev <llvm-dev at lists.llvm.org>
Reply-To: Joseph <cybercheesecake2 at gmail.com>
Date: Saturday, August 15, 2020 at 6:53 AM
To: llvm-dev <llvm-dev at lists.llvm.org>
Subject: [llvm-dev] Adding bitcode to an existing MachO object file

This is a silly question, but I am in a situation where I need to build x86 and
arm assembly sources for some sources while the rest will be built with C. I do
know that just adding `-fembed-bitcode` to a C sources would embed bitcode, but
doing the same for the assembly files will not do that (at least, it will add
the 1-byte `_LLVM,__asm` section, but not the `__LLVM,__bitcode` section).
Furthermore, I do need the final output to contain bitcode for all files used.

So, my question is if it is possible to add the `__LLVM,__bitcode` section later
to the MachO object file. I tried to archive the bitcode using `xar` and run
`llvm-objcopy main.o --add-section=__LLVM,__bitcode=main.xar main2.o`, but it
failed with an `unsupported load command`. This seems to be the case for all
usages of `llvm-objcopy` with MachO files.

Cheers and thanks

-- Joseph
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Many thanks for your comment! I was using the one from Brew (llvm 10, I
believe). I'll build master and run it from there and report back tomorrow

On Sat, 15 Aug 2020, 20:45 Shoaib Meenai, <smeenai at fb.com> wrote:
> What version of llvm-objcopy are you using? I know it’s had many fixes for
> Mach-O recently. If you’re running into a bug with the latest llvm-objcopy
> (from the master branch), it’d be great if you could file a bug on
> bugs.llvm.org with your input file (if possible).
>
>
>
> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of
Joseph
> via llvm-dev <llvm-dev at lists.llvm.org>
> *Reply-To: *Joseph <cybercheesecake2 at gmail.com>
> *Date: *Saturday, August 15, 2020 at 6:53 AM
> *To: *llvm-dev <llvm-dev at lists.llvm.org>
> *Subject: *[llvm-dev] Adding bitcode to an existing MachO object file
>
>
>
> This is a silly question, but I am in a situation where I need to build
> x86 and arm assembly sources for some sources while the rest will be built
> with C. I do know that just adding `-fembed-bitcode` to a C sources would
> embed bitcode, but doing the same for the assembly files will not do that
> (at least, it will add the 1-byte `_LLVM,__asm` section, but not the
> `__LLVM,__bitcode` section). Furthermore, I do need the final output to
> contain bitcode for all files used.
>
> So, my question is if it is possible to add the `__LLVM,__bitcode` section
> later to the MachO object file. I tried to archive the bitcode using `xar`
> and run `llvm-objcopy main.o --add-section=__LLVM,__bitcode=main.xar
> main2.o`, but it failed with an `unsupported load command`. This seems to
> be the case for all usages of `llvm-objcopy` with MachO files.
>
> Cheers and thanks
>
> -- Joseph
>
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