Re: [Devel] [patch 4/5] Fix aligment issues

[Lin Ming <ming.m.lin at intel.com>]

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On Tue, 2010-07-06 at 20:24 +0800, malattia(a)linux.it wrote:
> On Tue, Jul 06, 2010 at 09:19:47AM +0800, Lin Ming wrote:
> > On Mon, 2010-07-05 at 20:03 +0800, malattia(a)linux.it wrote:
> > > Add more platforms to the list of the ones requiring aligned memory access. Also
> > > fix callsites where wrong assumptions where made in terms of aligment.
> ...
> > > Index: b/executer/exoparg2.c
> > > ===================================================================
> > > --- a/executer/exoparg2.c	2010-07-02 21:42:26.477349196 +0900
> > > +++ b/executer/exoparg2.c	2010-07-04 11:18:22.506529460 +0900
> > > @@ -248,6 +248,8 @@
> > >      ACPI_OPERAND_OBJECT     **Operand = &WalkState->Operands[0];
> > >      ACPI_OPERAND_OBJECT     *ReturnDesc1 = NULL;
> > >      ACPI_OPERAND_OBJECT     *ReturnDesc2 = NULL;
> > > +    UINT64                  ReturnValue1 = 0;
> > > +    UINT64                  ReturnValue2 = 0;
> > >      ACPI_STATUS             Status;
> > >  
> > > 
> > > @@ -281,8 +283,10 @@
> > >  
> > >          Status = AcpiUtDivide (Operand[0]->Integer.Value,
> > >                                 Operand[1]->Integer.Value,
> > > -                               &ReturnDesc1->Integer.Value,
> > > -                               &ReturnDesc2->Integer.Value);
> > > +                               &ReturnValue1, &ReturnValue2);
> > 
> > Why need to replace &ReturnDesc1->Integer.Value with &ReturnValue1?
> 
> I get this on sparc systems without these 2 hunks:
> 
> malattia(a)smetana:~/acpica-unix> ./compiler/iasl -tc -ps.hex tests/misc/grammar.asl
> 
> Intel ACPI Component Architecture
> ASL Optimizing Compiler version 20100528 [Jul  6 2010]
> Copyright (c) 2000 - 2010 Intel Corporation
> Supports ACPI Specification Revision 4.0a
> 
> [1]    28389 bus error  ./compiler/iasl -tc -ps.hex tests/misc/grammar.asl
> 
> it is caused by the pointer to the 64bit integer being aligned to 4
> bytes instead of 8 bytes as required by the 64bit assigment inside
> AcpiUtDivide when computing the result of the division:
> 
>         *OutQuotient = InDividend / InDivisor;
> 
> or at least that is my understanding of the problem.
> 
> Anyway, just using a temporary variable correctly aligned on the stack
> and then assigning the result to Integer.Value afterwards works around
> the problem.
> 
> Hope the explanation is understandable... otherwise I'll try harder :)

Thanks for the clear explanation.

Lin Ming