On Nov 21, 2017, at 11:18 PM, Ben Coman <btc@openinworld.com> wrote:

Hi Todd,

Could you advise the the Playground code to use to test this?

And maybe a C program that links to the microclang shared library that does the equivalent test?

cheers -ben

On 22 November 2017 at 13:38, Todd Blanchard <tblanchard@mac.com> wrote:

 

I've been trying to track this down for a couple weeks now.

I have concluded that structs passed by value to functions on the 64 bit VM are not properly populated.  The struct's memory is all zero'd.

I found this while trying to work with LibClang and found that functions that fetched code locations from code ranges always returned invalid zero'd locations.  After spending some time with lldb I have traced the problem into the native code and found that the argument is not correct.

I've carved out the wee bit of clang to reproduce this in a tiny library.

The gist of it is below and the entire file is included.  Basically the struct passed to the function clang_getRangeStart is zero'd memory regardless of the data I send from the image side.

The build command I used on sierra is clang -shared -undefined dynamic_lookup -o microclang.dylib microclang.c

I'm stuck.  The FFI64 plugin is way beyond my comprehension.

// microclang.c

typedef struct {

  const void *ptr_data[2];

  unsigned int_data;

} CXSourceLocation;

/**

 * \brief Identifies a half-open character range in the source code.

 *

 * Use clang_getRangeStart() and clang_getRangeEnd() to retrieve the

 * starting and end locations from a source range, respectively.

 */

typedef struct {

  const void *ptr_data[2];

  unsigned begin_int_data;

  unsigned end_int_data;

} CXSourceRange;

const char* first = "first_pointer";

const char* second = "second_pointer";

// return a fake range with non zero data

CXSourceRange clang_getArbitraryRange()

{

  CXSourceRange range = {0};

  range.ptr_data[0] = (void*)first;

  range.ptr_data[1] = (void*)second;

  range.begin_int_data = 17;

  range.end_int_data = 24;

  return range;

}

// Actual clang function - range is always zero'd here despite having values in the image

CXSourceLocation clang_getRangeStart(CXSourceRange range) {

  // Special decoding for CXSourceLocations for CXLoadedDiagnostics.

  if ((uintptr_t)range.ptr_data[0] & 0x1) {

    CXSourceLocation Result = { { range.ptr_data[0], nullptr }, 0 };

    return Result;    

  }

  

  CXSourceLocation Result = { { range.ptr_data[0], range.ptr_data[1] },

    range.begin_int_data };

  return Result;

}