Delphi XE6 link C code in iOS

Question

I've built an App on Android using Delphi XE6 that requires C code. However on iOS I cannot make it work. I suspect the problem is related to arm/thumb status, but I am not sure. There is no problem in either system to call the C code from Pascal. But if the C code calls back a Pascal procedure iOS generates a "bad system call (12)"

Here is the pascal code:

function testarm(a,b:integer):integer; cdecl; external "testC.o";

Procedure testC;
Begin
  testarm(1,2);
end;

function BackToPascal(a,b:integer): integer; cdecl;
  Begin
  result := a+b;
end;

......

exports
  BackToPascal;

And here is the C code:

extern int BackToPascal(int a,int b);

extern int testarm(int a,int b)
{
   int i;
   i = BackToPascal(a,b);
   return i+1;
}

On android this is how I am compiling (It is working):

..."arm-linux-androideabi-gcc.exe" -c test.c -o test.o -O3 -mfloat-abi=softfp -mfpu=neon -marm -march=armv7-a -mtune=cortex-a8

On ios:

xcrun -sdk iphoneos clang -c -arch armv7 test.c -O3 -mfpu=neon -mtune=cortex-a8 -marm -march=armv7-a -mfloat-abi=softfp

I suspect that my xcode settings are wrong but I cannot figure out why.

When I debug, the error comes when calling testC in testarm when calling BackToPascal ( on "bl 0x8b8390 Xgobj.BackToPascal (int, int)" ). On Android it works perfect however the bl does not call directly BackToPascal, but the following code:

75A82D94 12C68FE2         add r12, pc, #18874368 ; 0x1200000
75A82D98 73CA8CE2         add r12, r12, #471040 ; 0x73000
75A82D9C 40F2BCE5         ldr pc, [r12, #576]! ; 0x240

Which get into BackToPascal

Jariah

There is some talk on similar threads of static functions being an issue and taking out static helped. Not enough code to see in your case if this is so. hth – Peashooter

iOS is 64bit, does the pascal interface with the int values compile to platform ints? I had many issues when going to 64bit, as we had inherited loads of code with tons of "int" inside. We had to replace them with NSInteger to make the application work properly on 64bit. – Smoking

As of the time of this question, Embarcadero had released Delphi XE8. Have you tried latest Delphi? – Park

Is it possible to be a problem of calling convention link (try adding pascal to "extern int BackToPascal(int a,int b);")? – Snavely

Answer 1

The code looks proper and your calling convention handling is, to my eyes, perfectly correct.

I think you may have ran into a possible/rumoured bug in Apple's ARM clang where calling a static function (which may happen behind the scenes e.g. for type conversion) from a static function may cause stack corruption. You're not doing so directly, but extern functions may be implemented through a stub which calls an anonymous static function containing the implementation.

You can try having your extern function be a wrapper which only calls a non-static implementation function instead.

Erinn