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

[Joe Abbey]

Looks to me like it converted the ? into the ascii hexadecimal representation _3F_.  I don't think another underscore was pre-pended.

This is probably thanks to lib/Target/Mangler.cpp.  You'll want to let ? be treated as an acceptable character.

static bool isAcceptableChar(char C, bool AllowPeriod) {
  if ((C < 'a' || C > 'z') &&
      (C < 'A' || C > 'Z') &&
      (C < '0' || C > '9') &&
      C != '_' && C != '$' && C != '@' && 
      !(AllowPeriod && C == '.'))
    return false;
  return true;
}

But you might want to add doesAllowQuestionMarksInName() to MCAsmInfo, it's possible that other name manglers don't accept question marks.

Cheers,
 
Joe Abbey
Software Architect
Arxan Technologies, Inc.
1305 Cumberland Ave, Ste 215
West Lafayette, IN 47906
jabbey at arxan.com
www.arxan.com



On Nov 25, 2011, at 10:39 AM, Michael Spencer wrote:

> 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
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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