Re: Passing function pointer to fcall

[wp1068189-ssc <stefan.sonnenberg@pythonmeister.com>]

I did figure this out already.
Anyway thanks alot.
 
Just a few days away newLisp 10.3.8 will be released - and then bring support
for
libffi on Windows, Linux and Mac OS. 


Anthony Green <green@moxielogic.com> hat am 7. Dezember 2011 um 13:01
geschrieben:

> Stefan,
>
>    The problem below is "avalues[3] = &printf".  You need to add one
> more level of indirection.. so...
>
> void *p = printf;
>   and
> avalues[3] = &p;
>
> AG
>
>
> On 11/27/2011 9:12 AM, Stefan Sonnenberg-Carstens wrote:
> > So, I extended the program some more:
> >
> > #include<stdio.h>
> > #include<ffi.h>
> > #include<stdlib.h>
> > #include<windows.h>
> >
> > int add(int a,int b, char *fmt,void *fn) {
> >      // int (*func)(char *,int) = (int (*)(char
> > *,int))GetProcAddress(GetModuleHandle("msvcrt.dll"),fn);
> >      int (*func)(char *,int) = (int (*)(char *,int))fn;
> >      return func(fmt,a+b);
> > }
> >
> > int main(void)
> >      {
> >
> >      ffi_cif cif;
> >      ffi_abi abi;
> >      ffi_status status;
> >      int nargs = 4;
> >      ffi_type *rtype =&ffi_type_sint32;
> >      ffi_type *atypes[4];
> >      void *avalues[4];
> >      int result;
> >
> >      int a,b;
> >      a = 3;
> >      b = 4;
> >
> >      char *fmt = "The answer is %i\n";
> >      char *fn  = "printf";
> >
> >      atypes[0] =&ffi_type_sint32;
> >      atypes[1] =&ffi_type_sint32;
> >      atypes[2] =&ffi_type_pointer;
> >      atypes[3] =&ffi_type_pointer;
> >
> >      avalues[0] = malloc(atypes[0]->size);
> >      avalues[1] = malloc(atypes[1]->size);
> >
> >      *(int *) avalues[0] = a;
> >      *(int *) avalues[1] = b;
> >      avalues[2] = (char *)&fmt;
> >      avalues[3] =&printf;
> >
> >      printf("direct call: %i",add(3,4,"erg: %i\n",&printf));
> >
> >      status = ffi_prep_cif(&cif, FFI_DEFAULT_ABI, nargs, rtype, atypes);
> >
> >      if(status != FFI_OK)
> >          printf("ffi_prep_cif failed (%i)\n",status);
> >
> >      // crash occurs somewhere near here ...
> >      ffi_call(&cif,FFI_FN(add),&result,avalues);
> >
> >      printf("%i\n",result);
> >
> >      return 0 ;
> >
> >      }
> >
> >
> > As you can see, I call my add function twice, once directly
> > and once via ffi_call.
> > Both times I pass a reference to printf.
> > As the direct method works, I guess the principal code is OK.
> >
> > Now, when I run the program it shows:
> >
> > $ dyn_callback.exe
> > erg: 7
> > direct call: 7
> >
> > Then it crashes and creates this callstack:
> >
> > dyn_callback.exe caused an Access Violation at location 614c25ff Reading
> > from location 614c25ff.
> >
> > Registers:
> > eax=614c25ff ebx=0040138c ecx=00000000 edx=00000003 esi=45206472
> > edi=6085db86
> > eip=614c25ff esp=0022fe34 ebp=0022fe60 iopl=0         nv up ei pl nz na pe
> > nc
> > cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000           
> >  efl=00000202
> >
> > Call stack:
> > AddrPC     AddrReturn AddrFrame  AddrStack  Params
> > 614C25FF   004013AF   0022FE30   0022FE34   00403064   00000007   77C35C94
> >    77C12580
> > 614C25FF
> > 004013AF   6B746957   0022FE60   0022FE34   00000003   00000004   00403064
> >    614C25FF
> > 004013AF  dyn_callback.exe:004013AF  add  dyn_callback.c:10
> >
> >         ...
> >             int (*func)(char *,int) = (int (*)(char *,int))fn;
> >             return func(fmt,a+b);
> >>         }
> >         int main(void)
> >         ...
> >
> > 6B746957   6B7465AF   0022FE78   0022FE34   6B746298   0022FEB4   00000010
> >    00000001
> > 6B746957  libffi-6.dll:6B746957  ffi_call_win32
> > 6B7465AF   004014FB   0022FEC8   0022FE34   0022FF20   0040138C   0022FEFC
> >    0022FF00
> > 6B7465AF  libffi-6.dll:6B7465AFC:\MinGW\msys\1.0\local\bin\libffi-6.dll:
> > No symbol found
> >    ffi_call
> > 004014FB   004010B9   0022FF58   0022FE34   00000001   005B2C98   005B2ED0
> >    00405004
> > 004014FB  dyn_callback.exe:004014FB  main  dyn_callback.c:53
> >
> >         ...
> >             ffi_call(&cif,FFI_FN(add),&result,avalues);
> >
> >>         printf("%i\n",result);
> >         return 0 ;
> >         ...
> >
> > 004010B9   00401284   0022FFA0   0022FE34   00000001   A47CBD08   7C90DCBA
> >    7C817064
> > 004010B9  dyn_callback.exe:004010B9  __mingw_CRTStartup  crt1.c:244
> >
> > 00401284   7C817067   0022FFC0   0022FE34   6085DB86   45206472   7FFDA000
> >    C0000005
> > 00401284  dyn_callback.exe:00401284  WinMainCRTStartup  crt1.c:274
> >
> > 7C817067   00000000   0022FFF0   0022FE34   0040126C   00000000   00000000
> >    00000000
> > 7C817067  kernel32.dll:7C817067
> > C:\WINDOWS\system32\kernel32.dll: No symbols
> >    RegisterWaitForInputIdle
> > DEBUG_EVENT:
> >         dwDebugEventCode = EXIT_PROCESS_DEBUG_EVENT
> >         dwProcessId = CCC
> >         dwThreadId = A30
> >         dwExitCode = C0000005
> >
> > I installed libffi 3.0.11 beforhand, but sadly it produces no debugging
> > symbols.
> >
>
>