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

On Ubuntu 16.04 I used...

$ clang -shared -fPIC -o libmicroclang.so microclang.c

$ clang test.c -L. -l microclang

test.c:6:53: error: no member named 'begin_int_data' in 'CXSourceLocation'

if(clang_getRangeStart(clang_getArbitraryRange()).begin_int_data == 0)

I presume you meant...

if(clang_getRangeStart(clang_getArbitraryRange()).int_data == 0)

so correcting and continuing...

$ clang test.c -L. -l microclang

$ LD_LIBRARY_PATH=. ./a.out

That failed

So I'm not sure how to proceed.

I was expecting that would work while Pharo failed.

Now interestingly...

$ clang test.c microlang.c

$ ./a.out

That worked

So it seems a similar problem exists outside our FFI.

cheers -ben

P.S. I refactored you code to extract a header file (attached)

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;
}