Re: [libvirt PATCH 1/3] virNWFilterRuleDefFixup: Factor out ethHdr as variable

On Fri, Sep 17, 2021 at 02:58:09PM +0200, Tim Wiederhake wrote: > This helps to bring down the frame size of virNWFilterRuleDefFixup, > as it > exceeds 8192 bytes when libvirt is build with sanitizers enabled, > in debug > mode, on clang. > > Signed-off-by: Tim Wiederhake <twiederh(a)redhat.com&gt; > --- >  src/conf/nwfilter_conf.c | 16 ++++++++-------- >  1 file changed, 8 insertions(+), 8 deletions(-) > > diff --git a/src/conf/nwfilter_conf.c b/src/conf/nwfilter_conf.c > index a3109962af..62334edeec 100644 > --- a/src/conf/nwfilter_conf.c > +++ b/src/conf/nwfilter_conf.c > @@ -2189,23 +2189,23 @@ virNWFilterRuleValidate(virNWFilterRuleDef > *rule) >  static void >  virNWFilterRuleDefFixup(virNWFilterRuleDef *rule) >  { > +    ethHdrDataDef *ethHdr; > + >  #define COPY_NEG_SIGN(A, B) \ >      (A).flags = ((A).flags & ~NWFILTER_ENTRY_ITEM_FLAG_IS_NEG) | \ >                  ((B).flags &  NWFILTER_ENTRY_ITEM_FLAG_IS_NEG); >   >      switch (rule->prtclType) { >      case VIR_NWFILTER_RULE_PROTOCOL_MAC: > -        COPY_NEG_SIGN(rule->p.ethHdrFilter.ethHdr.dataSrcMACMask, > -                      rule->p.ethHdrFilter.ethHdr.dataSrcMACAddr); > -        COPY_NEG_SIGN(rule->p.ethHdrFilter.ethHdr.dataDstMACMask, > -                      rule->p.ethHdrFilter.ethHdr.dataDstMACAddr); > +        ethHdr = &rule->p.ethHdrFilter.ethHdr; > +        COPY_NEG_SIGN(ethHdr->dataSrcMACMask, ethHdr- > >dataSrcMACAddr); > +        COPY_NEG_SIGN(ethHdr->dataDstMACMask, ethHdr- > >dataDstMACAddr); I don't get why this reduces stack size at all ? COPY_NEG_SIGN is just doing a bitwise and + or + assignment which doesn't require any intermediate variables. Regards, Daniel