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Re: [Qemu-devel] [PATCH for-2.0] configure: add option to disable -fstac

From: Noonan, Steven
Subject: Re: [Qemu-devel] [PATCH for-2.0] configure: add option to disable -fstack-protector flags
Date: Fri, 28 Mar 2014 18:04:37 +0000
User-agent: Microsoft-MacOutlook/

On 3/28/14, 10:51 AM, "Paolo Bonzini" <address@hidden> wrote:

>Il 28/03/2014 18:41, Laurent Desnogues ha scritto:
>>> > +  gcc_flags="-fstack-protector-strong -fstack-protector-all"
>>> > +  for flag in $gcc_flags; do
>>> > +    if compile_prog "-Werror $flag" "" ; then
>>> > +      QEMU_CFLAGS="$QEMU_CFLAGS $flag"
>>> > +      LIBTOOLFLAGS="$LIBTOOLFLAGS -Wc,$flag"
>>> > +      break
>>> > +    fi
>>> > +  done
>>> >  fi
>> My understanding is that -fstack-protector, -fstack-protector-strong,
>> and -fstack-protector-all are strictly ordered in terms of the number
>> of functions that are checked, so you have changed the default
>> behavior to check less functions for compilers that support
>> -fstack-protector-strong.  Is that what you had in mind?
>Yes.  -fstack-protector-all adds protection in places where it doesn't
>really matter, and that's why it has such a high cost.

Correct, -fstack-protector-all was too high impact. Sadly
-fstack-protector-strong seems to only exist in RedHat-provided compilers,
which I don't always use -- thus the new default this change provides
doesn't really help, so I'd need to just do 'configure
--disable-stack-protector' to avoid the performance penalty.

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