Re: [Xen-devel] [PATCH 2/2] xen: arm: traps: correct cond

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-09-21 at 17:08 +0800, Peng Fan wrote:
> On Mon, Sep 21, 2015 at 11:10:11AM +0100, Julien Grall wrote:
> > Hi Peng,
> > 
> > On 21/09/15 08:07, Peng Fan wrote:
> > > From "G6.2.29 CPSR, Current Program Status Register" of Aarch64 ARM
> > > and "B1.3.3 Program Status Registers (PSRs)" of ARMv7-A ARM:
> > > "
> > 
> > The section number may change between the different version of the
> > spec.
> > Can you also precise the spec version?
> > 
> > For instance on my ARM64 spec (ARM DDI 0497A.d) the section G6.2.29
> > points to "CSSELR" and not "CPSR".
> > 
> > > IT[7:5] holds the base condition for the IT block. The base condition
> > > is
> > >         the top 3 bits of the condition code specified by the first
> > >   condition field of the IT instruction.
> > > IT[4:0] encodes the size of the IT block, which is the number of
> > >         instructions that are to be conditionally executed, by the
> > >   position of the least significant 1 in this field. It also
> > >   encodes the value of the least significant bit of the condition
> > >   code for each instruction in the block.
> > > "
> > > So should be "cond = ( it >> 5 );" but not "cond = ( it >> 4 );"
> > 
> > IT[7:5] encodes the top 3 bits of the condition code and one bit of
> > IT[4:0] will contain the least significant bit of the condition code.
> > 
> > In order to get the full condition code you have to use IT[7:4] which
> > the current code does (see A2.5.2 ARM DDI 0406C.b).
> > 
> > So the current code looks valid to me. Did I miss something?
> 
> No, you are correct.

Were these two patches motivated by an actual issue you were seeing? Or
just from code inspection?


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