From: sandmann AT clio DOT rice DOT edu (Charles Sandmann)
Message-Id: <9606052140.AA12180@clio.rice.edu>
Subject: bugs (fwd)
To: djgpp-workers AT delorie DOT com
Date: Wed, 5 Jun 1996 16:40:19 -0600 (CDT)
Content-Type: text
Content-Length: 2492      

I didn't look at this in any detail, just FYI.

Forwarded message:
> From: Matthias Grimrath <y0001032 AT ws DOT rz DOT tu-bs DOT de>
> Date: Wed, 5 Jun 1996 19:06:08 +0100 (MESZ)
> 
> ------- Bugs in the C Compiler -------
> // Two bugs are in here:
> // 1.) CC1 always extends a value in a register to a long, even
> // if it is not necessary. In (3), c needs to be zero extend
> // from a byte to a short, but CC1 produces a 'andl $255,%eax'.
> // 'subb %ah,%ah' would be enough.
> //
> // 2.) Obviously CC1 is unware about the fact, that the
> // 'call/jmp' instructions can be used with a
> // memory operand. A 'call [dword ptr address]' (Intel syntax)
> // can be written in AT&T syntax as 'call address(,1)'
> //
> // compile with gcc -S -O3 and look how (3) and (4) are compiled
> #include <stdio.h>
> 
> long test(unsigned char b, unsigned short c, long d, char *s, int num)
>      __attribute__ (( regparm(3) ));
> 
> unsigned short jaja;
> 
> long test(unsigned char a, unsigned short c, long d, char *s, int num)
> {
>   jaja = c + a; // (3)
>   return d;
> }
> 
> long (*procptr)(unsigned char b, unsigned short c, long d, char *s, int num)
>      __attribute__ (( regparm(3) )) = test;
> 
> int main(void)
> {
>   procptr(2, 1, 3, "You see\n", 0); // (4)
>   cprintf("don't you?\n");
> }
> 
> 
> ------------ Bugs in as -----------
> A line like
>       movw    +0x8(%ebp),%ax
> doesn't assemble. Why is a '+' prefix not allowed?
> 
> gas doesn't decides on the phase of the moon whether or
> not to ignore segment prefixes. It ignores it only for
> reg/mem or mem/reg operands, where reg is 'eax' and mem is
> an absolute address.
> 
> gas also ignores segment prefixes for the string instructions.
> 
> I once downloaded the sources for gas and found that gas ignores
> segment prefixes only for those instructions which have a
> memory address but not an r/m field in the instruction pattern.
> Gas checks for the presence of this field whether this instruction
> can have a prefix or not.
> 
> To work around, you may also type the segment registers as
> instructions, e.g. 'fs; mov (%ebx),%ax' instead of typing
> '.byte XX; ...'
> 
> ---------------- Other bugs -----------
> the LIMITS.H include file doesn't check for signed or unsigned
> characters!
> 
> ---------------- Bugs in FSDB ----------
> lgs lkjkl,%eax not printed
> 
> ret xxx - xxx should be a number but really is junk
> 
> segment overrides for string instructions are not shown.
> 
> 'lcall' is disassembled as 'call'