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

From: Brad Smith
Subject: Re: [Qemu-devel] [PATCH for-2.0] configure: add option to disable -fstack-protector flags
Date: Fri, 28 Mar 2014 16:53:20 -0400
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On 28/03/14 2:04 PM, Noonan, Steven wrote:
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
+      break
+    fi
+  done
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.

-fstack-protector-strong exists in OpenBSD's GCC and now LLVM too.

I'd very much be interested in seeing this go in as we're already
using -strong in our own package.

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