[Bug c/34001] New: Incorrect __attribute__ fastcall behavior

[Bug c/34001] New: Incorrect __attribute__ fastcall behavior

[zia at aracnet dot com]

4byte structures that are passed as parameters to a fastcall routine will get
passed as registers. This does not match the original fastcall convention,
which passes such structures on the stack.

Compiling this code:
#include <stdio.h>

typedef struct {
  int a;
} my_struct;

int __attribute__((fastcall)) foo(my_struct s, int b)
{
  return s.a + b;
}


main()
{
  my_struct ss;
  ss.a = 1;
  printf("\nfoo = %d.\n",foo(ss,2));
}

Results in:
.
.
        movl    $1, -12(%ebp)
        movl    -12(%ebp), %ecx
        movl    $2, %edx
        call    _foo
.
.
and
.
.
.globl _foo
_foo:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $24, %esp
        movl    %ecx, -12(%ebp)
        movl    %edx, -16(%ebp)
        movl    -12(%ebp), %eax
        addl    -16(%ebp), %eax
        leave
        ret

With GCC.

Using other compilers that support fastcall will pass the struct value on the
stack.


-- 
           Summary: Incorrect __attribute__ fastcall behavior
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: zia at aracnet dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect __attribute__ fastcall behavior

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |normal


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect __attribute__ fastcall behavior

[hjl at lucon dot org]

------- Comment #1 from hjl at lucon dot org  2007-11-08 17:12 -------
I verified that it isn't fixed in gcc 4.3.0.


-- 

hjl at lucon dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-11-08 17:12:05
               date|                            |
   Target Milestone|---                         |4.3.0
            Version|4.0.1                       |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect __attribute__ fastcall behavior

[hjl at lucon dot org]

------- Comment #2 from hjl at lucon dot org  2007-11-09 16:55 -------
From

http://msdn2.microsoft.com/en-us/library/6xa169sk(VS.80).aspx

"The first two DWORD or smaller arguments are passed in ECX and EDX registers;
all other arguments are passed right to left."

But it isn't clear if it applies to structure/union. We tested all MS compilers
we have and verified that the above doesn't apply to structure/union. To make
fastcall compatible with MS compilers, we should only put scalar arguments
in ECX and EDX.


-- 

hjl at lucon dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |hjl at lucon dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-11-08 17:12:05         |2007-11-09 16:55:09
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect __attribute__ fastcall behavior

[hjl at lucon dot org]

------- Comment #3 from hjl at lucon dot org  2007-11-09 17:34 -------
A patch is posted at

http://gcc.gnu.org/ml/gcc-patches/2007-11/msg00531.html


-- 

hjl at lucon dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2007-
                   |                            |11/msg00531.html
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect x86 fastcall behavior

[hjl at lucon dot org]

------- Comment #4 from hjl at lucon dot org  2007-11-12 03:27 -------
>From "info gcc",

`fastcall'
     On the Intel 386, the `fastcall' attribute causes the compiler to
     pass the first argument (if of integral type) in the register ECX
                              ^^^^^^^^^^^^^^^^^^^
     and the second argument (if of integral type) in the register EDX.
                              ^^^^^^^^^^^^^^^^^^^
     Subsequent and other typed arguments are passed on the stack.
     The called function will pop the arguments off the stack.  If the
     number of arguments is variable all arguments are pushed on the
     stack.

It looks like gcc document follows MS compiler and we didn't implement
it correctly.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect x86 fastcall behavior

[hjl at lucon dot org]

------- Comment #5 from hjl at lucon dot org  2007-11-16 04:52 -------
The correct patch is at

http://gcc.gnu.org/ml/gcc-patches/2007-11/msg00885.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect x86 fastcall behavior

[hjl at lucon dot org]

------- Comment #6 from hjl at lucon dot org  2007-11-26 23:19 -------
We have changed fastcall behavior from gcc 3.4 to 4.1. For

---
#define FASTCALL __attribute((fastcall))

double FASTCALL  f_dii( double p1d, int p2i, int p3i ){  return p1d +
(double)p2
i + (double)p3i;  }

int    test_x;
int    test_y;
double test_d1;

void caller( void ){
  f_dii( test_d1, test_x, test_y );
}
---

Gcc 3.4 doesn't pass the first 2 integral parameters in ecx/edx and gcc
4.1 does.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect x86 fastcall behavior

[hjl at lucon dot org]

------- Comment #7 from hjl at lucon dot org  2007-11-27 02:36 -------
(In reply to comment #6)
> We have changed fastcall behavior from gcc 3.4 to 4.1. For
> 
> ---
> #define FASTCALL __attribute((fastcall))
> 
> double FASTCALL  f_dii( double p1d, int p2i, int p3i ){  return p1d +
> (double)p2
> i + (double)p3i;  }
> 
> int    test_x;
> int    test_y;
> double test_d1;
> 
> void caller( void ){
>   f_dii( test_d1, test_x, test_y );
> }
> ---
> 
> Gcc 3.4 doesn't pass the first 2 integral parameters in ecx/edx and gcc
> 4.1 does.
> 

This patch

http://gcc.gnu.org/ml/gcc-patches/2005-01/msg00541.html

fixes this fast call bug by changing the abi.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect x86 fastcall behavior

[hjl at gcc dot gnu dot org]

------- Comment #8 from hjl at gcc dot gnu dot org  2007-11-28 01:20 -------
Subject: Bug 34001

Author: hjl
Date: Wed Nov 28 01:20:34 2007
New Revision: 130488

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=130488
Log:
2007-11-27  H.J. Lu  <hongjiu.lu@intel.com>
            Joey Ye <joey.ye@intel.com>

        PR target/34001
        * config/i386/i386.c (function_arg_32): Don't pass aggregate
        arguments in ECX/EDX for fastcall.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/i386/i386.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001

[Bug target/34001] Incorrect x86 fastcall behavior

[hjl at lucon dot org]

------- Comment #9 from hjl at lucon dot org  2007-11-28 01:25 -------
Fixed in gcc 4.3.


-- 

hjl at lucon dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34001