Re: long long on 32-bit machines

Re: long long on 32-bit machines

[Arnd Bergmann]

H.P.A wrote:

> Does anyone happen to know if there are *any* 32-bit architectures (on 
> which Linux runs) for which the ABI for a "long long" is different from 
> passing two "longs" in the appropriate order, i.e. (hi,lo) for bigendian 
> or (lo,hi) for littleendian?

Some architectures require long long arguments to be passed as an
even/odd register pair. For example on s390, 

   void f(int a, int b, long long x) 

uses registers 2, 3, 4 and 5, while 

   void f(int a, long long x, int b)

uses registers 2, 4, 5 and 6. AFAIK, mips does the same, probably others
as well.

       Arnd <><

Re: long long on 32-bit machines

[Daniel Jacobowitz]

On Wed, Jan 28, 2004 at 08:22:01PM +0100, Arnd Bergmann wrote:
> 
> H.P.A wrote:
> 
> > Does anyone happen to know if there are *any* 32-bit architectures (on 
> > which Linux runs) for which the ABI for a "long long" is different from 
> > passing two "longs" in the appropriate order, i.e. (hi,lo) for bigendian 
> > or (lo,hi) for littleendian?
> 
> Some architectures require long long arguments to be passed as an
> even/odd register pair. For example on s390, 
> 
>    void f(int a, int b, long long x) 
> 
> uses registers 2, 3, 4 and 5, while 
> 
>    void f(int a, long long x, int b)
> 
> uses registers 2, 4, 5 and 6. AFAIK, mips does the same, probably others
> as well.

Yes.  Also, IIRC, one of SH3 and SH4 requires the padding, and the
other doesn't.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

Re: long long on 32-bit machines

[Paul Mackerras]

H. Peter Anvin writes:

> Does system calls follow the same convention?

Yes.  A system call with a long long argument will be handled by a C
routine in the kernel.  The system call arguments in r3 - r8 are
unchanged by the system call exception entry code and end up being the
arguments to the C routine.

Paul.

Re: long long on 32-bit machines

[H. Peter Anvin]

Paul Mackerras wrote:
> H. Peter Anvin writes:
> 
> 
>>Does anyone happen to know if there are *any* 32-bit architectures (on 
>>which Linux runs) for which the ABI for a "long long" is different from 
>>passing two "longs" in the appropriate order, i.e. (hi,lo) for bigendian 
>>or (lo,hi) for littleendian?
> 
> 
> Are you are talking about passing arguments to a function?  PPC32
> passes long long arguments in two registers in the order you would
> expect (hi, lo), BUT you have to use an odd/even register pair.  In
> other words, if you have a function like this:
> 
> 	int foo(int a, long long b)
> 
> then a will be passed in r3 and b will be passed in r5 and r6, and r4
> will be unused.
> 

Does system calls follow the same convention?

	-hpa

Re: long long on 32-bit machines

[Paul Mackerras]

H. Peter Anvin writes:

> Does anyone happen to know if there are *any* 32-bit architectures (on 
> which Linux runs) for which the ABI for a "long long" is different from 
> passing two "longs" in the appropriate order, i.e. (hi,lo) for bigendian 
> or (lo,hi) for littleendian?

Are you are talking about passing arguments to a function?  PPC32
passes long long arguments in two registers in the order you would
expect (hi, lo), BUT you have to use an odd/even register pair.  In
other words, if you have a function like this:

	int foo(int a, long long b)

then a will be passed in r3 and b will be passed in r5 and r6, and r4
will be unused.

Regards,
Paul.

Re: long long on 32-bit machines

[Arnd Bergmann]

On Thursday 29 January 2004 02:34, H. Peter Anvin wrote:

> If I remember correctly, a 6-argument system call on s390 will put a
> pointer to the last two arguments as the effective 5th argument, so this
> would not affect the system call calling convention, correct?

Almost. I think this is only relevant for mmap2(), where we pass a single
pointer to a struct with all six arguments, but the result is the same.

I don't know where I got the misinformation about the register pairs
on s390, but I verified that the problem exists on MIPS and PowerPC.
See sys32_ftruncate64 in arch/mips/kernel/linux32.c and 
arch/ppc64/kernel/sys_ppc32.c. PA-RISC appearantly work around this
by defining their own system call handlers with separate high/low
arguments, so they effectively work like i386 and s390. 

	Arnd <><

Re: long long on 32-bit machines

[H. Peter Anvin]

Ulrich Weigand wrote:
> Arnd Bergmann wrote:
> 
> 
>>Some architectures require long long arguments to be passed as an
>>even/odd register pair. For example on s390, 
>>
>>  void f(int a, int b, long long x) 
>>
>>uses registers 2, 3, 4 and 5, while 
>>
>>  void f(int a, long long x, int b)
>>
>>uses registers 2, 4, 5 and 6.
> 
> 
> Actually, this isn't quite true -- the second case will also
> use registers 2, 3, 4, and 5.
> 
> However, there is still a case where a single long long is
> passed differently from a pair of longs: when there is only
> a single register remaining for parameters.
> 
> This means that
>   void f(int a, int b, int c, int d, long e, long f)
> is passed as
>   a-d in register 2-5
>   e in register 6
>   f on the stack (4 bytes)
> 
> while
>   void f(int a, int b, int c, int d, long long e)
> is passed as
>   a-d in register 2-5
>   nothing in register 6
>   e on the stack (8 bytes)
>  

If I remember correctly, a 6-argument system call on s390 will put a
pointer to the last two arguments as the effective 5th argument, so this
would not affect the system call calling convention, correct?

	-hpa

Re: long long on 32-bit machines

[Ulrich Weigand]

Arnd Bergmann wrote:

>Some architectures require long long arguments to be passed as an
>even/odd register pair. For example on s390, 
>
>   void f(int a, int b, long long x) 
>
>uses registers 2, 3, 4 and 5, while 
>
>   void f(int a, long long x, int b)
>
>uses registers 2, 4, 5 and 6.

Actually, this isn't quite true -- the second case will also
use registers 2, 3, 4, and 5.

However, there is still a case where a single long long is
passed differently from a pair of longs: when there is only
a single register remaining for parameters.

This means that
  void f(int a, int b, int c, int d, long e, long f)
is passed as
  a-d in register 2-5
  e in register 6
  f on the stack (4 bytes)

while
  void f(int a, int b, int c, int d, long long e)
is passed as
  a-d in register 2-5
  nothing in register 6
  e on the stack (8 bytes)
 
Bye,
Ulrich 

-- 
  Dr. Ulrich Weigand
  weigand@informatik.uni-erlangen.de

Re: long long on 32-bit machines

[David S. Miller]

On Wed, 28 Jan 2004 14:12:50 -0500
Timothy Miller <miller@techsource.com> wrote:

> I don't know how it is for GCC, but when using the Sun compiler, "long 
> long" for 32-bit is low-high, while "long long" (or just long) for 
> 64-bit is high-low.  This has been an annoyance to me.  :)

For 64-bit it goes into a single 64-bit register.
And for 32-bit the sequence is high 32-bits low 32-bits.
At least on Sparc.

extern void foo(long long a);
void bar(void)
{
    foo(1);
}
/* gcc -m32 -S -o bar.s bar.c */
bar:
	!#PROLOGUE# 0
	save	%sp, -104, %sp
	!#PROLOGUE# 1
	mov	0, %o0
	mov	1, %o1
	call	foo, 0
	 nop
	nop
	ret
	restore
/* gcc -m64 -S -o bar.s bar.c */
bar:
	!#PROLOGUE# 0
	save	%sp, -192, %sp
	!#PROLOGUE# 1
	mov	1, %o0
	call	foo, 0
	 nop
	nop
	return	%i7+8

Re: long long on 32-bit machines

[Timothy Miller]

H. Peter Anvin wrote:
> Hi all,
> 
> Does anyone happen to know if there are *any* 32-bit architectures (on 
> which Linux runs) for which the ABI for a "long long" is different from 
> passing two "longs" in the appropriate order, i.e. (hi,lo) for bigendian 
> or (lo,hi) for littleendian?
> 
> I'd like to switch klibc to use the 64-bit file ABI thoughout, but it's 
> a considerable porting effort, and I'm trying to figure out how to best 
> manage it.
> 

I don't know how it is for GCC, but when using the Sun compiler, "long 
long" for 32-bit is low-high, while "long long" (or just long) for 
64-bit is high-low.  This has been an annoyance to me.  :)

long long on 32-bit machines

[H. Peter Anvin]

Hi all,

Does anyone happen to know if there are *any* 32-bit architectures (on 
which Linux runs) for which the ABI for a "long long" is different from 
passing two "longs" in the appropriate order, i.e. (hi,lo) for bigendian 
or (lo,hi) for littleendian?

I'd like to switch klibc to use the 64-bit file ABI thoughout, but it's 
a considerable porting effort, and I'm trying to figure out how to best 
manage it.

	-hpa