[Vm-dev] FFI Struct Argument Pass By Value Fails on Mac 64 bit
Ben Coman
btc at openinworld.com
Fri Nov 24 07:54:09 UTC 2017
On 24 November 2017 at 13:16, Ben Coman <btc at openinworld.com> wrote:
>
>
> On 22 November 2017 at 21:59, Ben Coman <btc at openinworld.com> wrote:
>
>>
>>
>> On 22 November 2017 at 13:38, Todd Blanchard <tblanchard at 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)
>>
>
> The issue is still beyond my ken, but I've made some progress towards
> isolating/understanding the issue.
> Attached zip exploded here for easy reference...
>
>
> ___microlang.h___
> typedef unsigned uintptr_t;
>
> typedef struct {
> const void *ptr_data[2];
> } CXSourceRange_;
>
> CXSourceRange_ clang_getArbitraryRange_();
> int clang_getRangeEnd_(CXSourceRange_ range);
>
>
>
> ___microclang.c___
> #include "microclang.h"
> const char* libraryString = "library_pointer";
>
> CXSourceRange_ clang_getArbitraryRange_()
> { CXSourceRange_ range = {0};
> range.ptr_data[0] = (void*)libraryString;
> return range;
> }
>
> int clang_getRangeEnd_(CXSourceRange_ range)
> { // Special decoding for CXSourceLocations for CXLoadedDiagnostics.
> if ((uintptr_t)range.ptr_data[0] & 0x1)
> { return 0; }
> else
> { return 1; }
> }
>
>
>
>
> ___test.c___
> #include <stdio.h>
> #include "microclang.h"
> const char* localString = "local_pointer";
>
> void test( CXSourceRange_ range, char *note )
> { int result = clang_getRangeEnd_(range);
> if(result == 0)
> { printf("That failed (%s)\n", note); }
> else
> { printf("That worked (%s)\n", note); }
> }
>
> int main()
> { CXSourceRange_ range1 = clang_getArbitraryRange_();
> test(range1, "library string");
>
> CXSourceRange_ range2 = {0};
> range2.ptr_data[0] = (void*)localString;
> test(range2, "local string");
> }
>
>
>
> ___Makefile___
> default: clean static shared
>
> clean:
> rm -f *so *App
> @echo
>
> shared:
> clang -g -o libmicroclang.so -shared -fPIC microclang.c
> clang -g -o sharedApp test.c -L. -lmicroclang
> LD_LIBRARY_PATH=. ./sharedApp
> @echo
>
> static:
> clang -g -o staticApp test.c microclang.c
> ./staticApp
> @echo
>
>
>
> Now running...
> $ make > report
>
> gives...
> ___report___
> rm -f *so *App
>
> clang -g -o staticApp test.c microclang.c
> ./staticApp
> That worked (library string)
> That worked (local string)
>
> clang -g -o libmicroclang.so -shared -fPIC microclang.c
> clang -g -o sharedApp test.c -L. -lmicroclang
> LD_LIBRARY_PATH=. ./sharedApp
> That failed (library string)
> That worked (local string)
>
Further simplification dealing *only* with strings (see attached
sharedLibString.zip)
(also attached is clang3.zip as a step along the way)
___microclang.c___
typedef unsigned uintptr_t;
const char* myLibraryString = "library_pointer";
const char * lib_getLibraryString()
{ return myLibraryString;
}
int lib_testString( const char *aString )
{ unsigned test = (uintptr_t)aString & 0x1;
printf("\n test=%d, aString-->%d\n", test, (uintptr_t)aString);
if (test)
{ return 0; }
else
{ return 1; }
}
___test.c___
#include <stdio.h>
int lib_testString( const char *aString );
const char *lib_getLibraryString();
const char *localString = "local_pointer";
void test( int result, char *note )
{ if(result == 0)
{ printf("That failed (%s)\n", note); }
else
{ printf("That worked (%s)\n", note); }
}
int main()
{ const char * libraryString = lib_getLibraryString();
test(lib_testString(libraryString), "library string");
test(lib_testString(localString), "local string");
}
$ make > report
___report___
rm -f *so *App
clang -g -o staticApp test.c microclang.c
./staticApp
test=0, aString-->4196150
That worked (library string)
test=0, aString-->4196068
That worked (local string)
clang -g -o libmicroclang.so -shared -fPIC microclang.c
clang -g -o sharedApp test.c -L. -lmicroclang
LD_LIBRARY_PATH=. ./sharedApp
test=1, aString-->-792512599
That failed (library string)
test=0, aString-->4196484
That worked (local string)
cheers -ben
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