Re: [Chicken-users] c-string return question

[Felix]

> My point is, that this code is valid wrt. the manual and apparently
> valid given my understanding of what the C code tries to do:
> make it possible to return on stack strings.

Can you point out the relevant manual section?

> For me it ends up like this:
> 
> --------------- #define return(x) C_cblock C_r = 
> (C_mpointer(&C_a,(void*)(x))); goto
> --------------- #C_ret; C_cblockend static C_word C_fcall stub26(C_word 
> C_buf,C_word
> --------------- #C_a0) C_regparm; C_regparm static C_word C_fcall 
> stub26(C_word
> --------------- #C_buf,C_word C_a0){ C_word 
> C_r=C_SCHEME_UNDEFINED,*C_a=(C_word*)C_buf;
> --------------- #unsigned int ch=(unsigned int )C_num_to_unsigned_int(C_a0); 
> static
> --------------- #unsigned char off[6]={0xFC,0xF8,0xF0,0xE0,0xC0,0x00};
>  int size=5; C_char buf[7];
>  buf[6]='\0';
>  if (ch < 0x80) {
>    buf[5]=ch;
>  } else {
>    buf[size--]=(ch&0x3F)|0x80; ch=ch>>6;
>    while (ch) { buf[size--]=(ch&0x3F)|0x80; ch=ch>>6; }
>    /* Write the size information into the first byte */
>    ++size;
>    buf[size]=off[size]|buf[size];
>  }
>  return(buf+size);
> 
> C_ret:
> #undef return
> 
> return C_r;}
> ---------------
> 
> to be called like this:
> 
> ---------
> t3=C_a_i_bytevector(&a,1,C_fix(3));
> t4=C_i_foreign_unsigned_integer_argumentp(t2);
> t5=stub26(t3,t4);
> C_trace("##sys#peek-c-string");
> t6=*((C_word*)lf[5]+1);
> ((C_proc4)(void*)(*((C_word*)t6+1)))(4,t6,t1,t5,C_fix(0));}
> ---------
> 
> But somehow the "C_proc4" receives clobbered memory.

"stub26" is called as a normal C function and the returned buffer
will be clobbered if it points to (nonstatic) heap data.


cheers,
felix