[llvm-dev] ORC API C Standard/System Libraries

Andrew Reece via llvm-dev llvm-dev at lists.llvm.org
Tue Nov 12 12:48:32 PST 2019

Hi all,

First of all, I want to say that I really appreciate all the work that's
gone into LLVM, clang and the ORC API. I would be very unlikely to be doing
my current project if they weren't available.

I'm using the ORC API to JIT some C code (soon to be C++) on Windows.
(I was on LLVM 8.0.0 but it didn't handle the 'allocator' attribute so I
upgraded to LLVM 9.0.0.)

The JIT compiling works well for simple files, #included local files and
object files.
As soon as I start trying to use system libraries with functions, things
start to fall down.
I think this is largely just due to my ignorance of clang in general, but
any guidance would be greatly appreciated.

1) I get multiple warnings for the system headers (e.g. stdlib) of the form:
"warning: macro expansion producing 'defined' has undefined behavior"

Is there a way to prevent these warnings? Preferably only for the system
I tried -Wno-expansion-to-defined, -fms-extensions, -fms-compatibility-fms,
-compatibility-version=14.16.27023. I also tried to reference the system
library folder by -isystem, -internal-isystem and -c-isystem

2) Disregarding the warnings, I also get the following error message:
"JIT session error: Symbols not found: { malloc }"

I assumed this might be because I wasn't linking the standard library, so I
tried appending "msvcrt.lib" and "-stdlib=msvcrt.lib" but to no avail. Can
you use .lib files with clang on Windows?

How do I make sure that the symbols defined in the standard libraries are
available to my JIT?

Thanks for any help you can give!
All the best,
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