[Ecls-list] UFFI returning double is broken?

[anri p.]

Sorry for a delay.


Here are C function (from reconstructed bug example):

double c_fn( double a, double b) {
  return a * b;
}

and uffi definition:

(def-function ("c_fn" c_fn) ((a :double) (b :double)) :returning :double)



The resulting asm code for C function:

<c_fn>:
   0:	55                   	push   %ebp
   1:	89 e5                	mov    %esp,%ebp
   3:	dd 45 10             	fldl   0x10(%ebp)
   6:	dc 4d 08             	fmull  0x8(%ebp)
   9:	5d                   	pop    %ebp
   a:	c3                   	ret    


and UFFI wrapper:

<L1c_fn>:
 a60:	56                   	push   %esi
 a61:	53                   	push   %ebx
 a62:	e8 f4 fe ff ff       	call   95b <__x86.get_pc_thunk.bx>
 a67:	81 c3 2d 07 00 00    	add    $0x72d,%ebx
 a6d:	83 ec 34             	sub    $0x34,%esp
 a70:	e8 4b fd ff ff       	call   7c0 <ecl_process_env at plt>
 a75:	89 c6                	mov    %eax,%esi
 a77:	8d 44 24 2c          	lea    0x2c(%esp),%eax
 a7b:	39 86 58 01 00 00    	cmp    %eax,0x158(%esi)
 a81:	73 49                	jae    acc <L1c_fn+0x6c>
 a83:	8b 44 24 44          	mov    0x44(%esp),%eax
 a87:	89 04 24             	mov    %eax,(%esp)
 a8a:	e8 a1 fd ff ff       	call   830 <ecl_to_double at plt>
 a8f:	8b 44 24 40          	mov    0x40(%esp),%eax
 a93:	89 04 24             	mov    %eax,(%esp)
 a96:	dd 5c 24 10          	fstpl  0x10(%esp)
 a9a:	e8 91 fd ff ff       	call   830 <ecl_to_double at plt>
 a9f:	dd 44 24 10          	fldl   0x10(%esp)
 aa3:	dd 5c 24 08          	fstpl  0x8(%esp)
 aa7:	dd 1c 24             	fstpl  (%esp)
 aaa:	e8 21 fd ff ff       	call   7d0 <c_fn at plt>
 aaf:	89 44 24 1c          	mov    %eax,0x1c(%esp)
 ab3:	db 44 24 1c          	fildl  0x1c(%esp)
 ab7:	dd 1c 24             	fstpl  (%esp)
 aba:	e8 21 fd ff ff       	call   7e0 <ecl_make_double_float at plt>
 abf:	c7 46 04 01 00 00 00 	movl   $0x1,0x4(%esi)
 ac6:	83 c4 34             	add    $0x34,%esp
 ac9:	5b                   	pop    %ebx
 aca:	5e                   	pop    %esi
 acb:	c3                   	ret    
 acc:	e8 1f fd ff ff       	call   7f0 <ecl_cs_overflow at plt>
 ad1:	eb b0                	jmp    a83 <L1c_fn+0x23>
 ad3:	8d b6 00 00 00 00    	lea    0x0(%esi),%esi
 ad9:	8d bc 27 00 00 00 00 	lea    0x0(%edi,%eiz,1),%edi



I've also tried the same C function, but with casting result to an integer
and returning int signature, and it works fine. Compiling C code with
-mno-fp-ret-in-387 doesn't work ether. 

With a C function, which calls c_ref: 

 double ref( double a, double b) {
  return 2 * c_fn( a, b);
}


the asm listing is:

<ref>:
  33:	55                   	push   %ebp
  34:	89 e5                	mov    %esp,%ebp
  36:	dd 45 10             	fldl   0x10(%ebp)
  39:	dc 4d 08             	fmull  0x8(%ebp)
  3c:	5d                   	pop    %ebp
  3d:	d9 e8                	fld1   
  3f:	de c1                	faddp  %st,%st(1)
  41:	c3                   	ret    


So, i believe that an uffi wrapper should use ST register, instead of 
fildl and fstpl sequence.