[Skiboot] [PATCH 1/4] libpore: Fix incorrect mtspr instruction generation

[Cyril Bur]

On Tue, 2017-11-14 at 16:48 +1100, Stewart Smith wrote:
> Cyril Bur <cyril.bur at au1.ibm.com> writes:
> > From coverity defect 173758:
> > CID 173758 (#1 of 1): Unused value (UNUSED_VALUE)
> > assigned_value: Assigning value from (uint8_t)i_Rs << 21 to
> > mtsprInstOpcode here, but that stored value is overwritten before it can
> > be used.
> > 
> > This causes the generated mtspr to always move from register r0 as
> > opposed to the function parameter i_Rs.
> > 
> > Luckily the only call to getMtsprInstruction is:
> > getMtsprInstruction( 0, (uint16_t)i_regId );
> > the first parameter is the register so in an incredible stroke of luck,
> > the requirement is to generate a mtspr from r0.
> > 
> > Therefore no bug exists today, this is still a fairly important fix
> > because if anyone uses getMtsprInstruction() with a non zero first
> > parameter, it will cause them endless headache.
> > 
> > Fixes: CID 173758
> > Signed-off-by: Cyril Bur <cyril.bur at au1.ibm.com>
> > ---
> >  libpore/p9_stop_api.C | 10 ++++------
> >  1 file changed, 4 insertions(+), 6 deletions(-)
> > 
> > diff --git a/libpore/p9_stop_api.C b/libpore/p9_stop_api.C
> > index 26a14bbf..3f0b248d 100644
> > --- a/libpore/p9_stop_api.C
> > +++ b/libpore/p9_stop_api.C
> > @@ -255,12 +255,10 @@ static uint32_t getOrisInstruction( const uint16_t i_Rs, const uint16_t i_Ra,
> >   */
> >  static uint32_t getMtsprInstruction( const uint16_t i_Rs, const uint16_t i_Spr )
> >  {
> > -    uint32_t mtsprInstOpcode = 0;
> > -    uint32_t temp = (( i_Spr & 0x03FF ) << 11);
> > -    mtsprInstOpcode = (uint8_t)i_Rs << 21;
> > -    mtsprInstOpcode = ( temp  & 0x0000F800 ) << 5;
> > -    mtsprInstOpcode |= ( temp & 0x001F0000 ) >> 5;
> > -    mtsprInstOpcode |= MTSPR_BASE_OPCODE;
> > +    uint32_t mtsprInstOpcode = MTSPR_BASE_OPCODE;
> > +    uint32_t temp = ((i_Spr & 1F) << 5) | ((i_Spr & 0x8F) >> 5);
> > +
> > +    mtsprInstOpcode |= ((i_Rs & 0x1F) << 21) | ((temp & 0x03FF) << 11);
> >  
> >      return SWIZZLE_4_BYTE(mtsprInstOpcode);
> >  }
> 
> 
> libpore/p9_stop_api.C: In function ‘getMtsprInstruction’:
> libpore/p9_stop_api.C:259:31: error: invalid suffix "F" on integer constant
>      uint32_t temp = ((i_Spr & 1F) << 5) | ((i_Spr & 0x8F) >> 5);

Awkward sorry, do you want a fix, or does this mean you'll just take
the other patch?

>