[LLVMdev] Where does LLVM mangle characters from llvm-ir names while generating native code?

[Michael Spencer]

So I was taking a look at Microsoft C++ ABI support while on vacation,
and ran into a major issue. Given the following llvm-ir:

$ clang++ -S -emit-llvm -O3 mangling.cpp -o - -Xclang -cxx-abi -Xclang microsoft
; ModuleID = 'mangling.cpp'
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f80:128:128-v64:64:64-
v128:128:128-a0:0:64-f80:32:32-n8:16:32-S32"
target triple = "i686-pc-win32"

define i32 @"?heyimacxxfunction@@YAHXZ"() nounwind readnone {
entry:
  ret i32 42
}

Note the ?heyimacxxfunction@@YAHXZ. Now if I generate assembly (using
clang or llc) I get:

$ clang++ -S -O3 mangling.cpp -o - -Xclang -cxx-abi -Xclang microsoft
        .def     __3F_heyimacxxfunction@@YAHXZ;
        .scl    2;
        .type   32;
        .endef
        .text
        .globl  __3F_heyimacxxfunction@@YAHXZ
        .align  16, 0x90
__3F_heyimacxxfunction@@YAHXZ:          # @"?heyimacxxfunction@@YAHXZ"
# BB#0:                                 # %entry
        movl    $42, %eax
        ret

It turned the ? into _3F_, and prepended _ someplace. I get the same
symbol if I use integrated-as to generate an object file.

I've been unable thus far to find out exactly where this occurs. And
once I do find it, I'm not sure of the correct fix. I assume that LLVM
mangles the '?' because it means something special in the gas syntax.
There also has to be a way to communicate to llvm from clang that this
symbol should not receive a prepended _.

Thanks,

- Michael Spencer