[Bug inline-asm/23242] New: Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[Bug inline-asm/23242] New: Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[ianw at gelato dot unsw dot edu dot au]

Hi,

See the following snippet 

ianw@morrison:~$ gcc-snap -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f95,objc,obj-c++,ada,treelang
--prefix=/usr/lib/gcc-snapshot --enable-shared --with-system-zlib --disable-nls
--enable-__cxa_atexit --enable-libstdcxx-allocator=mt --enable-clocale=gnu
--enable-libstdcxx-debug --enable-java-gc=boehm --enable-java-awt=gtk
--with-java-home=/usr/lib/gcc-snapshot/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre
--enable-mpfr --disable-werror i486-linux-gnu
Thread model: posix
gcc version 4.1.0 20050719 (experimental)

ianw@morrison:~$ cat test.c
int main()
{
  volatile unsigned char old, new, *newp;

  newp = &new;

  /* this one works OK */
  __asm__ __volatile__("xchgb %0, %1"
  : "=r"(old), "=m"(new)
  : "0"(0xff), "m"(new) : "memory");

#ifdef DEREF
  /* this one doesn't */
    __asm__ __volatile__("xchgb %0, %1"
  : "=r"(old), "=m"(*newp)
  : "0"(0xff), "m"(*newp) : "memory");
#endif

  return 0;
}

ianw@morrison:~$ gcc-snap -Wall -o test test.c

ianw@morrison:~$ gcc-snap -DDEREF -Wall -o test test.c
/tmp/cc8YTeKG.s: Assembler messages:
/tmp/cc8YTeKG.s:30: Error: bad register name `%sil'

ianw@morrison:~$ gcc-snap -O2 -DDEREF -Wall -o test test.c

I believe this to be the cause of Debian bug #321291
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=321291) filed against the
libatomic_ops package (original author CC'd)

-- 
           Summary: Invalid %sil register chosen when dereferenced pointer
                    used in inline asm with -O0
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: inline-asm
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ianw at gelato dot unsw dot edu dot au
                CC: Hans dot Boehm at hp dot com,gcc-bugs at gcc dot gnu dot
                    org
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

Re: [Bug inline-asm/23242] New: Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[Andrew Pinski]

On Aug 4, 2005, at 8:32 PM, ianw at gelato dot unsw dot edu dot au 
wrote:

>   /* this one doesn't */
>     __asm__ __volatile__("xchgb %0, %1"
>   : "=r"(old), "=m"(*newp)
>   : "0"(0xff), "m"(*newp) : "memory");


This is not a bug.

r is selecting %sil which is a valid register for x86_64.

"r" is assuming that it is a full size register.

Use "Q" instead.

-- Pinski

PS The reason why I am CC you instead of writing this into bugzilla is 
because
bugzilla seems dead.

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[pinskia at physics dot uc dot edu]

------- Additional Comments From pinskia at physics dot uc dot edu  2005-08-05 01:35 -------
Subject: Re:  New: Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0


On Aug 4, 2005, at 8:32 PM, ianw at gelato dot unsw dot edu dot au 
wrote:

>   /* this one doesn't */
>     __asm__ __volatile__("xchgb %0, %1"
>   : "=r"(old), "=m"(*newp)
>   : "0"(0xff), "m"(*newp) : "memory");


This is not a bug.

r is selecting %sil which is a valid register for x86_64.

"r" is assuming that it is a full size register.

Use "Q" instead.

-- Pinski

PS The reason why I am CC you instead of writing this into bugzilla is 
because
bugzilla seems dead.



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[ianw at gelato dot unsw dot edu dot au]

------- Additional Comments From ianw at gelato dot unsw dot edu dot au  2005-08-05 02:17 -------
Subject: Re:  Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

On Fri, Aug 05, 2005 at 01:35:51AM -0000, pinskia at physics dot uc dot edu wrote:
> On Aug 4, 2005, at 8:32 PM, ianw at gelato dot unsw dot edu dot au 
> wrote:
> 
> >   /* this one doesn't */
> >     __asm__ __volatile__("xchgb %0, %1"
> >   : "=r"(old), "=m"(*newp)
> >   : "0"(0xff), "m"(*newp) : "memory");
>
> This is not a bug.
> 
> r is selecting %sil which is a valid register for x86_64.

Sorry if I'm missing something, I don't work with x86-64 much, but
isn't it a wrong to consider that register when I'm building for i486?

-i


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[rth at gcc dot gnu dot org]

------- Additional Comments From rth at gcc dot gnu dot org  2005-08-05 03:14 -------
No, because you still need to use "Q" to get a register that may be used
with a low-part.  Even on i486.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-05 03:32 -------
*** Bug 23243 has been marked as a duplicate of this bug. ***

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[Hans dot Boehm at hp dot com]

------- Additional Comments From Hans dot Boehm at hp dot com  2005-08-12 18:51 -------
Could we reopen this as a documentation bug?  I'm still confused, and the 
amount of discussion suggests I'm not alone.  Currently "r" is documented as 
meaning "general register", with no comments about operand size.  I naively 
interpreted this to mean that the size is infered from the operand, which it 
seems to be in other cases.

"Q" means "a, b, c, or d register for 8-bit instructions that do use upper 
halves".  I don't understand why this applies to xchg.  Did you mean "q"?

Why are 8 bit registers treated separately, but not 16-bit registers?  Why does 
this only appear to be true for X86?  This is unintuitive since it seems that 
the compiler has enough information to get this right; it just choses not to.

Hans



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[schwab at suse dot de]

------- Comment #8 from schwab at suse dot de  2008-10-21 21:42 -------
*** Bug 37887 has been marked as a duplicate of this bug. ***


-- 

schwab at suse dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |therealfroggey at gmail dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[schwab at suse dot de]

------- Comment #7 from schwab at suse dot de  2008-08-04 07:44 -------
*** Bug 37018 has been marked as a duplicate of this bug. ***


-- 

schwab at suse dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gcc at karrels dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242

[Bug inline-asm/23242] Invalid %sil register chosen when dereferenced pointer used in inline asm with -O0

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2008-06-12 21:22 -------
*** Bug 36514 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |codemasterhs at yahoo dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23242